Posts Tagged ‘astronomy’
Dummies on dark matter 1 – the missing galactic masses
Jacinta: So here’s where we try to educate ourselves on dark matter, just for the fun of it.
Canto: But we’re serious. Our blog’s motto is ‘Rise above yourself and grasp the world’, supposedly from the wisdom of Archimedes, and he meant the universe, or would’ve.
Jacinta: Well, smarter guys than us are trying to grasp dark matter, with limited success it seems.
Canto: Yeah but they’ve been smart enough to recognise that there’s this missing matter, when they look at galaxies and find they’re spinner faster than their observed mass suggests they should, because physical laws apparently tell us that the greater the mass, the greater the gravitational effect, which would cause a greater spin towards the black hole sun, I think. But when astrophysicists measure a galaxy’s mass – which must surely be a tricky process, but I think it’s about measuring light spectra – different molecules give off different electromagnetic waves, though how they manage to measure all that is beyond me – anyway when they measure the galaxy’s mass and its spin, the numbers are off by orders of magnitude. I think.
Jacinta: Galaxies contain hundreds of billions of stars, I hear, so they must’ve built some impressive measuring technology. Okay, first research – from Physics LibreTexts:
The mass of [our] Galaxy can be determined by measuring the orbital velocities of stars and interstellar matter.
The article I’m quoting from focuses on our galaxy as a more or less typical example. Our sun is orbiting the galaxy’s centre (a black hole presumably?) at 200 kilometres per second, and it’s calculated that it takes about 225 million years for a full orbit.
Canto: Orbital velocity sounds so much more legitimate than spin, methinks.
Jacinta: So I want to put this explanation of the Milky Way’s proposed mass in my own terms to try to understand it better. Imagine the Sun’s roughly circular orbit around the galaxy, which is shaped somewhere between a sphere and a more or less two-dimensional disc. As Newton worked out, in the case of a sphere like Earth, gravity acts to pull everything towards the centre. Our Sun, which lies in an outer arm of the galaxy, gets whipped around at great speed due to the large mass between it and the galaxy’s centre (some 26,000 light years away). Kepler’s third law comes into play here…
Canto: His third planetary law (from the NASA Science website):
The squares of the orbital periods of the planets are directly proportional to the cubes of the semi-major axes of their orbits. Kepler’s Third Law implies that the period for a planet to orbit the Sun increases rapidly with the radius of its orbit.
This was presumably simply an observational measurement from Kepler, but Newton and others found that, the further out from the Sun, the faster the planet moved, due to the greater accumulated mass in between. I think.
Jacinta: Uhh no. The period increases rapidly, not the velocity. The word ‘rapidly’ has led you astray. Naughty NASA Science website, it should have said that the period becomes longer, and not just because there’s a greater distance to travel but because the planet itself is revolving more slowly. Don’t forget that’s there’s relatively little, in fact very very very little mass, relatively speaking, added between Jupiter and the Sun than there is between Earth and the Sun. And here’s some figures: Earth is revolving round the Sun at about 107,000 km/h, Jupiter at around 47,051 km/h and Mercury at 170,500 km/h.
Canto: Okay, so galaxies are quite different from solar systems. So in the centuries after Kepler and Newton, astrophysicists used their theories, along with further developments, to measure the Milky Way’s mass, generally maintaining the theory that the vast majority of that mass lay between the Sun and the centre. This was assumed to be reasonable because:
The number of bright stars and the amount of luminous matter (meaning any material from which we can detect electromagnetic radiation) both drop off dramatically at distances of more than about 30,000 light-years from the galactic center.
But this assumption has turned out to be wrong, because we now know that there’s lots more matter well out from the centre, but it happens to be invisible – to us at least, and maybe to our instruments, but then if it’s undetectable how do we know it exists?
Jacinta: Well, Physics LibreTexts gives a good explanation:
We can understand how astronomers detected this invisible matter by remembering that according to Kepler’s third law, objects orbiting at large distances from a massive object will move more slowly than objects that are closer to that central mass. In the case of the solar system, for example, the outer planets move more slowly in their orbits than the planets close to the Sun. There are a few objects, including globular clusters and some nearby small satellite galaxies, that lie well outside the luminous boundary of the Milky Way. If most of the mass of our Galaxy were concentrated within the luminous region, then these very distant objects should travel around their galactic orbits at lower speeds than, for example, the Sun does. It turns out, however, that the few objects seen at large distances from the luminous boundary of the Milky Way Galaxy are not moving more slowly than the Sun.
So I added some italics to help us. If all the mass, or a vast majority, was located at the galaxy’s centre, as our sun with its massive mass is located at the centre of our local system, then this handful of luminous objects that are clearly part of our galaxy but further, sometimes much further, from the centre, should be travelling more slowly than the Sun, but instead they’re travelling faster.
Canto: Which presumably means unaccounted for mass, something to do with e = mc², more mass provides more energy, giving more velocity…
Jacinta: Yeah, something like. But light is a kind of energy, like electromagnetic energy, which presumably dark matter doesn’t have, but it must have energy if it has mass. Or must it?
Canto: Andrew Pontzen, in a Royal Institution lecture, tells us that, according to current calculations there should be five times more dark matter than visible matter, and it’s streaming through the planet, and our bodies, as we write…
Jacinta: Like neutrinos? Are neutrinos a kind of dark matter?
Canto: Ha, well that’s a good thought, maybe. Here’s a quote from an article in Nature India in early 2022:
Physicists have developed a mathematical model that may shed light on the identity of dark matter, the mysterious substance that far outweighs visible matter in the universe. Dark matter is not made of atoms or other known fundamental particles and doesn’t interact with any form of light or electromagnetic radiation, making it difficult to detect. The new model showed that a non-interacting or sterile neutrino is probably a dark matter particle and contributes to the mass of dark matter.
Jacinta: A sterile neutrino?
Canto: Yes, aka an inert neutrino – currently hypothetical, so outside of the Standard Model. The Wikipedia article on this is pretty comprehensive and complex… I’ll quote from the very beginning of the article, and then we can discuss it, hahaha:
Sterile neutrinos (or inert neutrinos) are hypothetical particles (neutral leptons – neutrinos) that interact only via gravity and not via any of the other fundamental interactions of the Standard Model. The term sterile neutrino is used to distinguish them from the known, ordinary active neutrinos in the Standard Model, which carry an isospin charge of ±+1/ 2 and engage in the weak interaction. The term typically refers to neutrinos with right-handed chirality (see right-handed neutrino), which may be inserted into the Standard Model.
Jacinta: Well, just to complicate this apparently dire situation of masses of matter or stuff we know nothing about, there’s also dark energy, which according to another Royal Institution presentation, this time by Peter Fisher in 2022, makes up even more of the unknown stuff in the universe than dark matter, leaving us in the dark about 96% of universal stuff. How can we be so incompetent?
Canto: Well, it’s an increasingly informed incompetence I’m sure. We’ve learned, as you say, that all the particulate matter-energy that we know about makes up only 4% of all there is, so now we (I mean you and I) need to learn how we (the astrophysics community) learned this.
Jacinta: About 73% of the unknown stuff is dark energy, 23% is dark matter. So let’s try to regurgitate Fisher’s talk in our own words, so that we can sound more informed.
Canto: Right so we start with the ‘big bang’ 13.7 billion years ago, followed by ‘inflation’, a very rapid expansion over a relatively short period, resulting in the cosmic background afterglow, after which the universe slows down markedly in its expansion thenceforward, with first stars and then galaxies developing. But then, after about half the life of the universe, it starts to expand slightly more rapidly, apparently due to dark energy.
Jacinta: Yes, according to an illustration I’ve seen before, and which we’ll post here, dark matter dominates in the first half of universe’s history, and dark energy dominates the second half.
Canto: And why might that be? That is presumably an unsolved mystery. Which we will continue to explore…
References
https://science.nasa.gov/resource/orbits-and-keplers-laws/
https://en.wikipedia.org/wiki/Sterile_neutrino
What is dark matter? With Peter Fisher (Royal Institution lecture, 2022)
reading matters 13: the glass universe
Canto: So The glass universe, published in 2016, has a cute title, referring as it does to the ‘glass ceiling’, another clever term for that invisible barrier up there that appears to prevent women from rising in politics, business and science, but also to the glass photographic plates upon which were recorded the spectrographic signatures of a vast arrays of stars, clusters and the like, in the decades of the late nineteenth century and early twentieth century, by a somewhat less vast array of human computers – the name given to the largely underpaid female stargazers and recorders of Harvard College observatory and elsewhere.
Jacinta: Yes, Dava Sobel, author of the fascinating little book Longitude, as well as Galileo’s Daughter, which is in a stack of books here waiting to be read, has brought to life a group of dedicated women and their male supporters over a period when the higher education of women was just starting to be addressed.
Canto: Yes, it all started with the Drapers, a wealthy and well-connected couple in the 1870s. Henry was a leading astronomer of the day, and ‘Mrs Henry’, aka Anna, a socialite and heiress. Their social evenings were mostly science-focused, with guests including the inventor Thomas Edison, the zoologist Alexander Agassiz, and Prof. Edward Pickering, of Harvard. Henry Draper was working on the chemical make-up of stars, using ‘a prism that split starlight into its spectrum of component colours’, for which he’d won great acclaim, when he died suddenly of a flu-like illness in his mid-forties. His devoted and rich widow, keen to continue his legacy, helped finance, along with Pickering, a continuation of his ground-breaking research.
Jacinta: And so the computers of Harvard College Observatory were born. We need to explain – or try to – the science of spectrographic analysis, but I’d like to first briefly describe some of the women who did this work. They include Williamina (Mina) Fleming, a canny Scotswoman frae Dundee (our birthplace), whose first American job was as the Pickering’s maid but who soon proved her worth as a star spotter and tracker, classifier, and organiser, leading the team of computers in the early decades. In 1899 she was given the title of ‘curator of astronomical photographs’, becoming the first titled female in the university’s history. As such she presided over 12 women ‘engaged in the care of the photographs; identification, examination and measurement of them; reduction of these measurements, and preparation of results for the printer’.
Canto: Far from just bureaucratic work – this would’ve involved a lot of learning and conjecture, noting patterns and anomalies and trying to account for them.
Jacinta: Absolutely. Antonia Maury, Annie Jump Cannon, Cecilia Payne-Gaposchkin, Henrietta Leavitt and the tragically short-lived Adelaide Ames were among the most noteworthy of these computers, and I should stop using the term, because they weren’t machines and they all made lasting contributions to the field…
Canto: And they all have their own Wikipedia pages. What more evidence do we need?
Jacinta: They contributed to academic papers, often without attribution, especially in the early years, and had their findings read out in academic institutions to which they were barred. Over time they became established teachers and lecturers, in the women’s colleges which started to become a thing in the twenties. But let’s get onto the daunting stuff of science. How were these glass plates created and what did they reveal?
Canto: So spectroscopy became a thing in the 1860s. Spectroscopes were attached to telescopes, and they separated starlight into ‘a pale strip of coloured light ranging from reddish at one end through orange, yellow, green, and blue to violet at the other’. I quote from the book. But what these changing colours meant exactly, as well as the ‘many black vertical lines interspersed at intervals along the coloured strip’, this was all something of a mystery, a code that needed to be cracked. Henry Draper had captured these spectral lines and intervals on photographic plates, which were bequeathed to Harvard by his widow. They formed the beginning of the collection.
Jacinta: The term spectrum was first used by Isaac Newton two centuries earlier, and he correctly claimed that this coloration wasn’t due to flaws in glass and crystals but was a property of light itself. The dark lines within the stellar spectra on Draper’s plates are called Fraunhofer lines, after a Bavarian lens-maker, Joseph von Fraunhofer, who built the first spectroscope. He at first thought the dark lines between the rainbow of colours his instrument produced were somehow artificial, but continued work convinced him that they were a natural effect. He gave them alphabetical labels according to their thickness, including the letter D for a double line in the pale orange region. He mapped hundreds of them, though today we’ve detected many thousands of them in sunlight. He didn’t understand what they were, though he realised they were something significant. Later in the 19th century Robert Bunsen and Gustav Kirchov conducted experiments with various chemical elements and found that they burned in colours around those black lines, which we now know as absorption lines.
Canto: Yes, it was Kirchov who connected the colours created by burning elements to the spectral lines that the sun’s light could be separated into, concluding that this great fireball of gases producing white light in the sky was actually a mixture of burning elements, or elements being transformed into other elements. As to the absorption lines, Sobel puts it this way:
As light radiated through the sun’s outer layers, the bright emission lines from the solar conflagration were absorbed in the cooler surrounding atmosphere, leaving dark telltale gaps in the solar spectrum.
These absorption lines, which together with emission lines, are spectral lines in the visible spectrum which ‘can be used to identify the atoms, elements or molecules present in a star, galaxy or cloud of interstellar gas’, to quote from this Swinburne University site.
Jacinta: So we’ll try to keep within the confines of the book, and the scientific developments of the period which these women, in particular, contributed to. So, rather, surprisingly to us modern wiseacres, these revelations about the sun as a super-hot fireball and a producer of elements was a bit hard for 19th century folk to take in, but scientists were excited. Henry Draper described spectral analysis as having ‘made the chemist’s arms millions of miles long’, and in 1872 he began photographing the spectra of other stars. It was long known that they had different colours and brightnesses – called ‘apparent luminosities’ – but spectral analysis provided more detailed data for categorisation, and sets of photographs revealed changes in luminosity and colour over time. Williamina Fleming, Harvard’s principal computer, took charge of Draper’s thousands of plates, which provided the most detailed spectral data of stars up to that time, and was able to analyse them into classes, via their absorption lines, in new and complex ways. It was cutting edge science.
Canto: There was also an interest in throwing more light, so to speak, on variable stars. They were so numerous and complex in their variability that Pickering needed more computers to track them. Lacking funds, he advertised for volunteers, emphasising the role of women in particular, whose effectiveness he’d seen plenty of evidence for.
Jacinta: Not to mention their willingness to work for less, or effectively nothing. These were often siblings or partners of astronomers or other scientists, with unfulfilled scientific ambitions. Later, though, came from the newly created ‘Ladies’ Colleges, such as Radcliffe and Wellesley.
Canto: The Orion Nebula was a particularly rich source of these variable stars, and Pickering found an ideal computer, Henrietta Leavitt, a Radcliffe graduate, to explore them. Within six months, she’d confirmed previous identifications of variables in the nebula and added more than 50 others, afterwards confirmed by Fleming. Then, using a combination of negative and positive glass plates, she found hundreds more, in the Orion Nebula and the Small Magellanic Cloud. As Pickering pointed out, due to the lack of resolution in the plates, this number was likely the tip of the iceberg. In writing up a report of her findings, Leavitt described a pattern she’d found: ‘It is worthy of notice… that the brighter variables [aka cepheid variables] have the longer periods’. This brightness (or luminosity) and its relationship to periodicity (the time taken to go through a full cycle of change) is now known as the Leavitt Law, though of course it took decades for Henrietta Leavitt to receive full recognition for discovering it.
Jacinta: Yes, it’s worth noting that these women worked painstakingly on data analysis, developing new and more rigorous classification systems, studying and theorising about anomalies, and communicating their findings to leading astronomers and researchers around the world. And it’s also worth noting that they were supported and highly appreciated at Harvard by Edward Pickering and his successor as Director of the Harvard College Observatory, Harlow Shapley – though of course there were plenty of naysayers.
Canto: Okay so we’ve spoken of two or three of the computer stars’, and there were many more, but let’s finish with the work of Antonia Maury.
Jacinta: Well we must also mention Annie Jump Cannon (great name), star classifier and photographer extraordinaire, suffragist and generally formidable persona, in spite of being almost completely deaf. She classified around 350,000 stars and contributed greatly to the Harvard Classification Scheme, the first international star classification system. Antonia Coetana de Paiva Pereira Maury (I’m not kidding), a graduate of Vassar College, was a niece of Henry Draper.
Canto: Not what you know but who you know?
Jacinta: It is partly that – and that cliché is worth a whole book to itself – but Maury was no slouch, she was a keen and observant star observer and systemiser. One important discovery she shared with Pickering was one of the first known binary star systems, in the handle of the Big Dipper. This required months of careful observation from 1887 through 1889, as they noted one spectral line separating into two then the lines merging again, then separating, with one line shifting slightly to the red end of the spectrum and the other to the blue. Once they recognised that they were dealing with binary star systems, others were soon found. And once these systems were confirmed, Maury carefully calculated their orbital periods and speeds.
Canto: There were many other important breakthroughs. Spectral colours, as we’ve pointed out, were connected to particular chemical elements, and Cecilia Payne, whose major focus was the measurement of stellar temperatures, found a superabundance in the elements hydrogen and helium, which confounded other experts and soon made her doubt her own calculations. Payne wrote up her findings in the Proceedings of the National Academy of Sciences in 1925, ‘admitting’ that the percentages of hydrogen and helium were ‘improbably high’ and ‘almost certainly not real’.
Jacinta: Yes, it’s well worth noting that the knowledge we have of stars today, which seems almost eternal to us, is in fact very recent. The book also covers the dispute between Harlow Shapley and Edwin Hubble – with many on either side of course – as to whether other galaxies existed. That dispute was only resolved in the thirties, and now we count other galaxies in the trillions. So the period covered in Sobel’s book was a truly transformative period in our understanding of the universe, as well as transformative in terms of women’s education and women’s participation in the most heavenly of all the sciences.
Canto: Whateva.
References
The glass universe, by Dava Sobel, 2016
https://science.nasa.gov/astrophysics/focus-areas/what-are-galaxies
https://en.wikipedia.org/wiki/Annie_Jump_Cannon
https://en.wikipedia.org/wiki/Antonia_Maury
https://en.wikipedia.org/wiki/Williamina_Fleming
how to define a planet: the problematic case of Pluto
A while back I listened to a podcast from Point of Inquiry, in which two planetary scientists, Alan Stern and David Grinspoon, involved in NASA’s New Horizons mission to Pluto, were separately interviewed, and were inevitably asked about Pluto’s demotion from planet status. Having not followed this issue, I was surprised at the response. So it’s time to take a closer look.
Of course I should be writing ecstatically about the New Horizons mission, not to mention those of Juno, Cassini, Mars’ Curiosity and so forth, and hopefully that will come, but the controversy about Pluto immediately struck me, as I thought, in my naïveté, that its demotion was a consensual thing amongst astronomers, with only the ignoroscenti (my neologism) left to mourn the fact (not that I mourned it particularly – Pluto still existed after all, and it didn’t care a jot what we thought of it).
Pluto, discovered by Clyde Tombaugh in 1930, was accepted as the ninth and final planet in our solar system for decades until the nineties, when another Kuiper belt object was discovered (besides Charon, Pluto’s large moon), and the Kuiper belt itself became a thing, in fact a massive thing, far bigger than the ‘familiar’ asteroid belt between Mars and Jupiter. We now know of more than 1000 kuiper belt objects, with at least 100,000 believed to exist. The Kuiper belt is widely spread out from the orbit of Neptune, and though Pluto is its largest and brightest object, it’s not the most massive. Presumably it’s for this reason that Pluto was demoted – what with the scattered disc and the Oort cloud there seemed to suddenly be a host of objects that could be included as planets, so it was thought better to exclude Pluto, or to demote it to dwarf planet status, presumably along with other assorted Kuiper belt objects (KBOs), rocks and iceballs that were worthy of the designation. That seemed okay to my thoughtless mind, but here’s what Alan Stern had to say on the subject:
Well, you know, we don’t really honour that classification in planetary science, that was really done by a group of different astronomers who don’t know much about planets. Let me give you a technical term, we call it BS. You know what BS stands for don’t you? Bad Science. Now you wouldn’t ask a podiatrist, a foot doctor, to help you if you had a cardiovascular problem with your heart, that’d be the wrong expertise, though they’re both doctors you’d be going for a cardiologist. And if you had a real estate problem you probably wouldn’t go to a divorce attorney, even though they’re both attorneys. In the space field we have many professions, we have engineering professions, we have many different scientific specialties, etc. Astronomers really don’t know much about planets any more than I’m an expert in black holes in faraway galaxies. They had a little meeting in 2006, they were worried that school children would have to memorise the names of too many planets, so they wrote a definition that limited the number of planets to eight. Now, right after that, Ira Flatow called me up on Science Friday and said, would you debate Mike Brown, who was one of the proponents of ‘let’s limit the planets to eight’, and I said, sure, and we got on the phone and it’s Science Friday live, and Mike Brown makes his case and says, ‘look we just can’t have 50 planets, it’s too many to remember.’ Now, I found that anti-scientific, it seems like engineering the definition, versus letting it inform you, but Ira said, Alan what’d you think, ‘can’t have 50 planets’, what d’you say back to MIke? I said, ‘well if you can’t have 50 planets then we’re probably going to have to go back to eight states, I guess’. And he was speechless…
I love that story – though no doubt Mike Brown would’ve told a different one. So let’s turn Stern’s objection into an inquiry. Was it scientifically correct/accurate/fair to reclassify Pluto as a dwarf/minor planet?
Happily I just happened to listen to a podcast of the Skeptics’ Guide a few days later, which has led me to a more detailed piece on Steven Novella’s Neurologica blog on the Pluto controversy. Apparently, in the above-mentioned 2006 meeting they decided that to be classified as a planet, a body in our solar system should meet 3 criteria:
- it has to orbit the sun
- it has to be spheroid (i.e. have the mass to be so, due to its gravity),
- it must have cleared its orbit of other objects.
Now this third criteria immediately seems the dodgiest, as it sounds like it’s designed to eliminate any KBOs. And how do we know an orbit is cleared? After all, one day, a comet or asteroid may strike us, because our orbits have coincided this time around. And why is that third criterion even important?
Novella cites a recent paper by planetary scientist Phillip Metzger who argues that the third criterion is invalid and that nothing about a body’s orbit should be in the definition since orbits can alter due to external influences. Only characteristics intrinsic to the body should be included in the definition. This would essentially leave one criterion standing – that of sphericity. And even then, how sphere-like does a planet have to be? Another ‘problem’ with Metzger’s definition is that it would include moons, such as our own, and many others. Novella has his own classifying suggestion, which sounds promising to me:
We keep criteria “a” and “b” and drop “c”. However, we add that the object must not be in a subservient orbit around a larger object. What does that mean? If two objects, like the Earth and Moon, are in orbit around each other, and the center of gravity (barycenter) lies beneath the surface of one of the bodies, then the smaller object will be said to orbit the larger object, and is a moon. Therefore Europa, which is large enough by itself to be a planet, would instead be considered a moon because it orbits Jupiter.
I need to further explain the term ‘barycentre’, for my own sake. Think of two bodies in gravitational relationship to each other. Inevitably, one of them will be more massive, and will exert a greater gravitational force. An obvious case is the Earth and the Moon. Between the two there is a point, the ‘centre of gravity’, or barycentre, around which the two bodies revolve, but because the Earth is a lot more massive that the Moon and they’re relatively close to each other, that barycentre is actually close enough to the Earth’s centre to be within the mass of the Earth, with the result that only the moon revolves. The Earth, though, is very much affected by the Moon’s gravitational field, which causes a slight wobble as well as tidal effects on the Earth’s surface.
Interestingly, Novella’s reclassification would include Charon, Pluto’s ‘moon’, as a planet (as well as Pluto of course) because its size relative to Pluto puts the barycentre at a point between the two bodies, rather than within Pluto. So Pluto-Charon would be reclassified as a binary-planet system. It would also promote Ceres, in the asteroid belt, and Eris and Makemake, two recently discovered Kuiper belt objects, to planetary status. That takes the current eight up to thirteen, with others yet to be discovered.
It’s unlikely of course that the astronomical overlords who reclassified Pluto would be swayed by any mere outsider’s view, however well-reasoned, but this examination of the issue is a reminder of just how dubious the reasoning of ‘experts’ can be, and how important it is to question that reasoning. Size apparently does matter to these guys, but this new category of ‘dwarf’ or ‘minor’ planet seems inherently unstable, and will probably become even more so as the number of discovered exoplanets increases. Will it be mass or volume that’s the decider, and what will be the mass or volume that decides? And does it really matter? It’s only nomenclature after all. And yet… The difference between an asteroid and a comet is important, is it not? And so is the difference between a planet and an asteroid. And so is the difference between a moon and a planet. And so… is it not?
the movements of the Earth, the ecliptic, the celestial sphere…
Why does the Earth spin? Initial conditions plus Newton’s first law is the basic explanation. And from these it should be easy to guess that it’s slowing down as tiny but inexorable forces act upon it, and it will continue to do so unless something unforeseeable happens. The tidal friction caused by the moon, which itself is decreasing over time (or at least I assume so, since the moon is spiralling away from us) is the Earth’s principal brake. Some say that Earth has been gradually slowing down since the last great collision, which created the moon, and which left the planet spinning full circle every six hours, but I think that’s still speculative.
Anyway, we don’t just rotate (in an anti-clockwise direction), we revolve (anti-clockwise) around the sun on a plane tilted at 23.4 degrees from our spin – that’s tilted from the perpendicular. But why? And there’s this thing called precession, right? Spin a top, as I did as a kid, and the most successful spin will have the least precession – the smallest circle (actually a cone) around which the axis of rotation wobbles, but as the top slows that cone will widen until all falls in a heap. In the Earth’s case, it’s most commonly called the precession of the equinoxes, or ‘the wobble’ (maybe).
So the Earth moves in mysterious ways, and I’ve barely begun. It orbits the sun – why? Its orbit is elliptical – why? Its rotational and revolutionary speed vary – why? And what about other movements – the solar system, the galaxy, the universe?
A cool video I’ve been watching tells me something I’d never known or thought of before. We’re all on meridian lines, which pass through us in a north-south direction, from the north pole to the south pole. Lines of longitude. When the sun is at its highest point in the sky, at noon, it’s aligned perfectly with our meridian. The shadow it casts, our shadow, thus points precisely to the north or south pole, depending on the sun’s position north or south of ‘directly overhead’. If the sun is directly overhead, congratulations, you’re on the sub-solar point, and your shadow will disappear beneath your feet, so to speak. Right now the sub-solar point is a circular area in the Atlantic, a little north of the equator, and just touching land in west Africa. I doubt if we ever experience it here in Australia, as it seems to hang close to the equator.
The point to make here is one about time. As there’s a meridian line for just about everyone, it follows that everyone on a different meridian is experiencing a different time. Noon, or any other time, isn’t the same for everyone – but that’s massively inconvenient, so we’ve regularised time via zones, so we can do our business.
Looking again at our rotation, we might think we have it nailed at very close to 24 hours per full rotation, but not quite, for all is relative. The sun, for example, has its movements too, as does everything else. We’ve found that, measured from a distant star, one meridian completes a revolution in 23.9 hours, also known as a sidereal day. Our calendars, though, are based on the solar day. As the Earth turns, it moves forward in its revolution around the sun. So by the time it has turned 360 degrees it needs to spin a little more for the same spot to be facing the sun as was the case 24 hours before. That slightly greater than 360 degree turn is what we call the solar day. From our perspective it seems like an exact 360-degree turn because we’re facing the sun again, exactly as the day before. Or so it seems.
We revolve around the sun in an ellipse. Or not precisely around the sun. Kepler’s first law of planetary motion, presented to the world without fanfare in 1609, had it that all the planets traced an elliptical orbit around a focal line, with the sun as one of its end-points, or foci. And while we’re at it, let’s look at Kepler’s three laws and how they were arrived at. The second law, presented in the same year, states that ‘a line segment joining a planet to the sun will sweep out an equal area over an equal time interval’, and the third law, announced to a largely indifferent world in 1618, is perhaps less linguistically elegant, or at any rate simple: ‘The square of the orbital period of a planet is proportional to the cube of the semi-major axis of its orbit.’ I ripped this from Wikipedia, the greatest gift to all dilettantes and autodidacts ever developed.
Kepler’s laws improved on those of Copernicus, but of course they accepted Copernicus’ heliocentric system as the basis. All Kepler really added was the eccentricity of planetary orbits, a minor detail really, but certainly an improvement. His laws weren’t presented as such at the time: they weren’t described as laws until Voltaire’s publication of Eléments de la philosophie de Newton, no doubt largely the work of his intellectual superior, Emilie du Chatelet.
So, the first two laws. Kepler was given access to some of the detailed astronomical data of his employer Tycho Brahe, who asked him to calculate precisely the orbit of Mars. Tycho apparently withheld the bulk of his observations from Kepler, because he suspected him of being one of those upstart heliocentrists. Kepler wanted, for largely mystical reasons, to define the Mars orbit as a perfect circle, but after years of trying the calculations wouldn’t work out. What he did discover was that, although the orbital path wasn’t circular – the sun was sometimes further away, sometimes closer – if you drew a line from Mars (or any other planet, including Earth) to the sun, and then another line, say exactly six days later, the triangle created always had the same area, no matter where you were in the orbit. For this to happen, the planet must be moving faster nearer the sun than when further from the sun. This was Kepler’s second law, which helped him to calculate the first. The planets’ orbits appeared to be elliptical. If the sun was offset from the centre of the planetary orbits, but still obviously essential to those orbits, then the offset could be calculated precisely such that all the planetary orbits fitted. And so it was. Most astronomers consider this to be his greatest contribution.
Kepler’s third law, with its interesting mathematical basis, provided the greatest inspiration to Newton:
The square of the orbital period of a planet is proportional to the cube of the semi-major axis of its orbit.
P2 = a3
I rarely do maths here, but surely this one’s simple enough even for me! The orbital period (p) of a planet is the time it takes to make a complete revolution around the sun. Note that it’s a measure of time, not distance. The semi-major axis of an ellipse is half its longest diameter. In the special case of a circle, it would be the radius. This law enables us, apparently, to determine the distance of planets from the sun, though it appears to entangle time and space. Generally these distances are given in relative terms. with the Earth’s distance from the sun given the value 1 AU (astronomical unit). By that reckoning, the outermost planet, Neptune, has a value of 30.06 AU, approximately, according to one site providing such data. Similarly, we reckon the orbital period in Earth years. Neptune’s orbital period is 164.79 years. So, for Neptune, 164.79² = 30.0611³. Try it on a calculator and you’ll find it doesn’t quite work out, but this may be due to eccentricity of orbits, in time and space. Other sites have different figures. The Kepler equation seems to capture the pattern rather than the precise detail. It’s probable that the publication of logarithmic tables between Kepler’s calculation of the first two laws and the third was vital.
I’m of course no expert on any of this – go to more reputable sites for a more complete story, though you’ll probably find what I found – a fair amount of interesting confusion.
I’ll finish with the ecliptic. The Earth’s orbit sketches out an elliptical plane, which we call the ecliptic. Then again, the ecliptic is also described as the apparent motion of the sun in the sky with respect to the fixed stars – not to be confused with the apparent daily movement caused by Earth’s rotation. In fact Wikipedia describes the ecliptic as ‘the mean plane in the sky that the sun follows in the course of a year’, and Wikipedia is always way more right than I am in these matters, but it’s confusing. The plane can be visualised as stretching out into space, way beyond the actual orbit around the sun and bounded within a celestial sphere, with a ‘celestial equator’, on the same plane as Earth’s equator, also marking a circular section of the sphere at 23.4° from the ecliptic. The north-south celestial axis, an extension of Earth’s axis to the celestial sphere, is again at an angle of 23.4°, on average, from the north-south ecliptic axis, which runs perpendicular to the ecliptic plane.
There’s more, but I’ll stop at this. The ecliptic plane for Earth is an average, as there are always perturbations. The other planets don’t follow this ecliptic precisely, but they’re not too far away, probably as a result of uniforming forces at the creation of the solar system.
the strange world of the self-described ‘open-minded’ – part three, Apollo
In 2009, a poll held by the United Kingdom’s Engineering & Technology magazine found that 25% of those surveyed did not believe that men landed on the Moon. Another poll gives that 25% of 18- to 25-year-olds surveyed were unsure that the landings happened. There are subcultures worldwide which advocate the belief that the Moon landings were faked. By 1977 the Hare Krishna magazine Back to Godhead called the landings a hoax, claiming that, since the Sun is 93,000,000 miles away, and “according to Hindu mythology the Moon is 800,000 miles farther away than that”, the Moon would be nearly 94,000,000 miles away; to travel that span in 91 hours would require a speed of more than a million miles per hour, “a patently impossible feat even by the scientists’ calculations.”
From ‘Moon landing conspiracy theories’ , Wikipedia
Time magazine cover, December 1968
Haha just for the record the Sun is nearly 400 times further from us than the Moon, but who’s counting? So now to the Apollo moon missions, and because I don’t want this exploration to extend to a fourth part, I’ll be necessarily but reluctantly brief. They began in 1961 and ended in 1975, and they included manned and unmanned space flights (none of them were womanned).
But… just one more general point. While we may treat it as inevitable that many people prefer to believe in hoaxes and gazillion-dollar deceptions, rather than accept facts that are as soundly evidence-based as their own odd existences, it seems to me a horrible offence in this case (as in many others), both to human ingenuity and to the enormous cost in terms, not only of labour spent but of lives lost. So we need to fight this offensive behaviour, and point people to the evidence, and not let them get away with their ignorance.
The Apollo program was conceived in 1960 during Eisenhower’s Presidency, well before Kennedy’s famous mission statement. It was given impetus by Soviet successes in space. It involved the largest commitment of financial and other resources in peacetime history. The first years of research, development and testing involved a number of launch vehicles, command modules and lunar modules, as well as four possible ‘mission modes’. The first of these modes was ‘direct ascent’, in which the spacecraft would be launched and operated as a single unit. Finally, after much analysis, debate and lobbying, the mode known as Lunar Orbit Rendezvous (LOR) was adopted. The early phases of the program were dogged by technical problems, developmental delays, personal clashes and political issues, including the Cuban missile crisis. Kennedy’s principal science advisor, Jerome Weisner, was solidly opposed to manned missions.
I can’t give a simple one-by-one account of the missions, as the early unmanned missions weren’t simply named Apollo 1, 2 etc. They were associated strongly with the Saturn launch vehicles, and the Apollo numbering system we now recognise was only established in April 1967. The Apollo 4 mission, for example, is also known as AS-501, and was the first unmanned test flight of the Saturn 5 launcher (later used for the Apollo 11 launch). Three Apollo/Saturn unmanned missions took place in 1966 using the Saturn 1B launch vehicle.
The manned missions had the most tragic of beginnings, as is well known. On January 27 1967 the three designated astronauts for the AS-204 spaceflight, which they themselves had renamed Apollo 1 to commemorate the first manned flight of the program, were asphyxiated when a fire broke out during a rehearsal test. No further attempt at a manned mission was made until October of 1968. In fact, the whole program was grounded after the accident for ‘review and redesign’ with an overall tightening of hazardous procedures. In early 1968, the Lunar Module was given its first unmanned flight (Apollo 5). The flight was delayed a number of times due to problems and inexperience in constructing such a module. The test run wasn’t entirely successful, but successful enough to clear the module for future manned flights. The following, final unmanned mission, Apollo 6, suffered numerous failures, but went largely unnoticed due to the assassination of Martin Luther King on the day of the launch. However, its problems helped NASA to apply fixes which improved the safety of all subsequent missions.
And so we get to the first successful manned mission, Apollo 7. Its aim was to test the Apollo CSM (Command & Service Module) in low Earth orbit, and it put American astronauts in space for the first time in almost two years. It was also the first of the three-man missions and the first to be broadcasted from within the spaceship. Things went very well in technical terms, a relief to the crew, who were only given this opportunity due to the deaths of the Apollo 1 astronauts. There were some minor tensions between the astronauts and ground staff, due to illness and some of the onboard conditions. They spent 11 days in orbit and space food, though on the improve, was far from ideal.
Apollo 8, launched only two months later in December, was a real breakthrough, a truly bold venture, as described in Earthrise, an excellent documentary of the mission made in 2005 (the astronauts were the first to witness Earthrise from the Moon). The aim, clearly, was to create a high-profile event designed to capture the world’s attention, and to eclipse the Soviets. As the documentary points out, the Soviets had stolen the limelight in the space race – ‘the first satellite, the first man in orbit, the first long duration flight, the first dual capsule flights, the first woman in space, the first space walk’. Not to mention the first landing of a human-built craft on the Moon itself.
One of the world’s most famous photos, Earthrise, taken by astronaut William Anders on Christmas Eve, 1968
The original aim of the mission was to test the complete spacecraft, including the lunar module, in Earth orbit, but when the lunar module was declared unready, a radical change of plan was devised, involving an orbit of the Moon without the lunar module. Apollo 8 orbited the Moon ten times at close quarters (110 kms above the surface) over a period of 20 hours. During the orbit they made a Christmas Eve telecast, the most watched program ever, up to that time. Do yourself a favour and watch the doco. The commentary of the astronaut’s wives are memorable, and put the moon hoaxers’ offensiveness in sharp relief.
By comparison to Apollo 8 the Apollo 9 mission (March ’69) was a modest affair, if that’s not too insulting. This time the complete spacecraft for a Moon landing was tested in low Earth orbit, and everything went off well, though space walking proved problematic, as it often had before for both American and Soviet astronauts, due to space sickness and other problems. With Apollo 10 (May ’69) the mission returned to the Moon in a full dress rehearsal of the Apollo 11 landing. The mission created some interesting records, including the fastest speed ever reached by a manned vehicle (39,900 kms/hour during the return flight from the Moon) and the greatest distance from home ever travelled by humans (due to the Moon’s elliptical orbit, and the fact that the USA was on the ‘far side of the Earth’ when the astronauts were on the far side of the Moon).
I’ll pass by the celebrated Apollo 11 mission, which I can hardly add anything to, and turn to the missions I know less – that’s to say almost nothing – about.
Apollo 12, launched in November 1969, was a highly successful mission, in spite of some hairy moments due to lightning strikes at launch. It was, inter alia, a successful exercise in precision targeting, as it landed a brief walk away from the Surveyor 3 probe, sent to the Moon two and a half years earlier. Parts of the probe were taken back to Earth.
The Apollo 13 mission has, for better or worse, come to be the second most famous of all the Apollo missions. It was the only aborted mission of those intended to land on the Moon. An oxygen tank exploded just over two days after launch in April 1970, and just before entry into the Moon’s gravitational sphere. This directly affected the Service Module, and it was decided to abort the landing. There were some well-documented hairy moments and heroics, but the crew managed to return safely. Mea culpa, I’ve not yet seen the movie!
Apollo 14, launched at the end of January 1971, also had its glitches but landed successfully. The astronauts collected quite a horde of moon rocks and did the longest moonwalk ever recorded. Alan Shepard, the mission commander, added his Moon visit to the accolade of being the first American in space ten years earlier. At 47, he’s the oldest man to have stepped on the Moon. The Apollo 15 mission was the first of the three ‘J missions’, involving a longer stay on the Moon. With each mission there were improvements in instrumentation and capability. The most well-known of these was the Lunar Roving Vehicle, first used on Apollo 15, but that mission also deployed a gamma-ray spectrometer, a mass spectrometer and a laser altimeter to study the Moon’s surface in detail from the command module. Apollo 16 was another successful mission, in which the geology of the Moon’s surface was the major focus. Almost 100kgs of rock were collected, and it was the first mission to visit the ‘lunar highlands’. The final mission, Apollo 17, was also the longest Moon stay, longest moonwalks in total, largest samples, and longest lunar orbit. And so the adventure ended, with high hopes for the future.
I’ve given an incredibly skimpy account, and I’ve mentioned very few names, but there’s a ton of material out there, particularly on the NASA site of course, and documentaries aplenty, many of them a powerful and stirring reminder of those heady days. Some 400,000 technicians, engineers, administrators and other service personnel worked on the Apollo missions, many of them working long hours, experiencing many frustrations, anxieties, and of course thrills. I have to say, as an internationalist by conviction, I’m happy to see that space exploration has become more of a collaborative affair in recent decades, and may that collaboration continue, defying the insularity and mindless nationalism we’ve been experiencing recently.
a beautiful image of the International Space Station, my favourite symbol of global cooperation
Finally, to the moon hoaxers and ‘skeptics’. What I noticed on researching this – I mean it really was obvious – was that in the comments to the various docos I watched on youtube, they had nothing to say about the science and seemed totally lacking in curiosity. It was all just parroted, and ‘arrogant’ denialism. The science buffs, on the other hand, were full of dizzy geekspeak on technical fixes, data analysis and potential for other missions, e.g. to Mars. In any case I’ve thoroughly enjoyed this little trip into the Apollo missions and the space race, in which I’ve learned a lot more than I’ve presented here.
the strange world of the self-described ‘open-minded’ – part one
my copy – a stimulating and fun read, great fodder for closed-minded types, comme moi
I’ve just had my first ever conversation with someone who at least appears to be sceptical of the Apollo 11 moon landing of 1969 – and, I can only suppose, the five subsequent successful moon landings. Altogether, twelve men walked on the moon between 20 July 1969 and December 10 1972, when the crew members of Apollo 17 left the moon’s surface. Or so the story goes.
This conversation began when I said that perhaps the most exciting world event I’ve experienced was that first moon landing, watching Neil Armstrong possibly muffing the lines about one small step for a man, and marvelling that it could be televised. I was asked how I knew that it really happened. How could I be so sure?
Of course I had no immediate answer. Like any normal person, I have no immediate, or easy, answer to a billion questions that might be put to me. We take most things on trust, otherwise it would be a very very painstaking existence. I didn’t mention that, only a few months before, I’d read Phil Plait’s excellent book Bad Astronomy, subtitled Misconceptions and misuses revealed, from astrology to the moon landing ‘hoax’. Plait is a professional astronomer who maintains the Bad Astronomy blog and he’s much better equipped to handle issues astronomical than I am, but I suppose I could’ve made a fair fist of countering this person’s doubts if I hadn’t been so flabbergasted. As I said, I’d never actually met someone who doubted these events before. In any case I don’t think the person was in any mood to listen to me.
Only one reason for these doubts was offered. How could the lunar module have taken off from the moon’s surface? Of course I couldn’t answer, never having been an aeronautical engineer employed by NASA, or even a lay person nerdy enough to be up on such matters, but I did say that the moon’s minimal gravity would presumably make a take-off less problematic than, say, a rocket launch from Mother Earth, and this was readily agreed to. I should also add that the difficulties, whatever they might be, of relaunching the relatively lightweight lunar modules – don’t forget there were six of them – didn’t feature in Plait’s list of problems identified by moon landing skeptics which lead them to believe that the whole Apollo adventure was a grand hoax.
So, no further evidence was proffered in support of the hoax thesis. And let’s be quite clear, the claim, or suggestion, that the six moon landings didn’t occur, must of necessity be a suggestion that there was a grand hoax, a conspiracy to defraud the general public, one involving tens of thousands of individuals, all of whom have apparently maintained this fraud over the past 50 years. A fraud perpetrated by whom, exactly?
My conversation with my adversary was cut short by a third person, thankfully, but after the third person’s departure I was asked this question, or something like it: Are you prepared to be open-minded enough to entertain the possibility that the moon landing didn’t happen, or are you completely closed-minded on the issue?
Another way of putting this would be: Why aren’t you as open-minded as I am?
So it’s this question that I need to reflect on.
I’ve been reading science magazines on an almost daily basis for the past thirty-five years. Why?
But it didn’t start with science. When I was kid, I loved to read my parents’ encyclopaedias. I would mostly read history, learning all about the English kings and queens and the battles and intrigues, etc, but basically I would stop at any article that took my fancy – Louis Pasteur, Marie Curie, Isaac Newton as well as Hitler, Ivan the Terrible and Cardinal Richelieu. Again, why? I suppose it was curiosity. I wanted to know about stuff. And I don’t think it was a desire to show off my knowledge, or not entirely. I didn’t have anyone to show off to – though I’m sure I wished that I had. In any case, this hunger to find things out, to learn about my world – it can hardly be associated with closed-mindedness.
The point is, it’s not science that’s interesting, it’s the world. And the big questions. The question – How did I come to be who and where I am? – quickly becomes – How did life itself come to be? – and that extends out to – How did matter come to be? The big bang doesn’t seem to explain it adequately, but that doesn’t lead me to imagine that scientists are trying to trick us. I understand, from a lifetime of reading, that the big bang theory is mathematically sound and rigorous, and I also know that I’m far from alone in doubting that the big bang explains life, the universe and everything. Astrophysicists, like other scientists, are a curious and sceptical lot and no ‘ultimate explanation’ is likely to satisfy them. The excitement of science is that it always raises more questions than answers, it’s the gift that keeps on giving, and we have human ingenuity to thank for that, as we’re the creators of science, the most amazing tool we’ve ever developed.
But let me return to open-mindedness and closed-mindedness. During the conversation described above, it was suggested that the USA simply didn’t have the technology to land people on the moon in the sixties. So, ok, I forgot this one: two reasons put forward – 1, the USA didn’t have the technological nous; 2, the modules couldn’t take off from the moon (later acknowledged to be not so much of an issue). I pretty well knew this first reason to be false. Of course I’ve read, over the years, about the Apollo missions, the rivalry with the USSR, the hero-worship of Yuri Gagarin and so forth. I’ve also absorbed, in my reading, much about spaceflight and scientific and technological development over the years. Of course, I’ve forgotten most of it, and that’s normal, because that’s how our brains work – something I’ve also read a lot about! Even the most brilliant scientists are unlikely to be knowledgeable outside their own often narrow fields, because neurons that fire together wire together, and it’s really hands-on work that gets those neurons firing.
But here’s an interesting point. I have in front of me the latest issue of Cosmos magazine, issue 75. I haven’t read it yet, but I will do. On my shelves are the previous 74 issues, each of which I’ve read, from cover to cover. I’ve also read more than a hundred issues of the excellent British mag, New Scientist. The first science mag I ever read was the monthly Scientific American, which I consumed with great eagerness for several years in the eighties, and I still buy their special issues sometimes. Again, the details of most of this reading are long forgotten, though of course I learned a great deal about scientific methods and the scientific mind-set. The interesting point, though, is this. In none of these magazines, and in none of the books, blogs and podcasts I’ve consumed in about forty years of interest in matters scientific, have I ever read the claim, put forward seriously, that the moon landings were faked. Never. I’m not counting of course, books like Bad Astronomy and podcasts like the magnificent Skeptics’ Guide to the Universe, in which such claims are comprehensively debunked.
The SGU podcast – a great source for exciting science developments, criticism of science reporting, and debunking of pseudo-science
Scientists are a skeptical and largely independent lot, no doubt about it, and I’ve stated many times that scepticism and curiosity are the twin pillars of all scientific enquiry. So the idea that scientists could be persuaded, or cowed into participating in a conspiracy (at whose instigation?) to hoodwink the public about these landings is – well let’s just call it mildly implausible.
But of course, it could explain the US government’s massive deficit. That’s it! All those billions spent on hush money to astronauts, engineers, technicians (or were they all just actors?), not to mention nosey reporters, science writers and assorted geeks – thank god fatty Frump is here to make America great again and lift the lid on this sordid scenario, like the great crusader against fake news that he is.
But for now let’s leave the conspiracy aspect of this matter aside, and return to the question of whether these moon landings could ever have occurred in the late sixties and early seventies. I have to say, when it was put to me, during this conversation, that the technology of the time wasn’t up to putting people on the moon, my immediate mental response was to turn this statement into a question. Was the technology of the time up to it? And this question then turns into a research project. In other words, let’s find out, let’s do the research. Yay! That way, we’ll learn lots of interesting things about aeronautics and rocket fuel and gravitational constraints and astronaut training etc, etc – only to forget most of it after a few years. Yet, with all due respect, I’m quite sure my ‘adversary’ in this matter would never consider engaging in such a research project. She would prefer to remain ‘open-minded’. And if you believe that the whole Apollo project was faked, why not believe that all that’s been written about it before and since has been faked too? Why believe that the Russians managed to get an astronaut into orbit in the early sixties? Why believe that the whole Sputnik enterprise was anything but complete fakery? Why believe anything that any scientist ever says? Such radical ‘skepticism’ eliminates the need to do any research on anything.
But I’m not so open-minded as that, so in my dogmatic and doctrinaire fashion I will do some – very limited – research on that very exciting early period in the history of space exploration. I’ll report on it next time.
So why exactly is the sky blue? SfD tries to investigate
Canto: Well, Karl Kruszelnicki is one of our best science popularisers as you know, and therefore a hero of ours, but I have to say his explanation of the blueness of our daily sky in his book 50 Shades of Grey left me scratching my head…
Jacinta: Not dumbed-down enough for you? Do you think we could form a Science for Dummies collaboration to do a better job?
Canto: Well that would really be the blind leading the blind, but at least we’d inch closer to understanding if we put everything in our own words… and that’s what I’m always telling my students to do.
Jacinta: So let’s get down to it. The day-sky is blue (or appears blue to we humans?) because…?
Canto: Well the very brief explanation given by Dr Karl is that it’s about Rayleigh scattering. Named for a J W Strutt, aka Lord Rayleigh, who first worked it out.
Jacinta: So let’s just call it scattering. What’s scattering?
Canto: Or we might call it light scattering. Our atmosphere is full of particles, which interfere with the light coming to us from the sun. Now while these particles are all more or less invisible to the naked eye, they vary greatly in size, and they’re also set at quite large distances from each other, relative to their size. The idea, broadly, is that light hits us from the sun, and that’s white light, which as we know from prisms and rainbows is made up of different wavelengths of light, which we see, in the spectrum that’s visible to us, as Roy G Biv, red orange yellow green blue indigo violet, though there’s more of some wavelengths or colours than others. Red light, because it has a longer wavelength than blue towards the other end of the spectrum, tends to come straight through from the sun without hitting too many of those atmospheric particles, whereas blue light hits a lot more particles and bounces off, often at right angles, and kind of spreads throughout the sky, and that’s what we mean by scattering. The blue light, or photons, bounce around the sky from particle to particle before hitting us in the eye so to speak, and so we see blue light everywhere up there. Now, do you find that a convincing explanation?
Jacinta: Well, partly, though it raises a lot of questions.
Canto: Excellent. That’s science for you.
Jacinta: You say there are lots of particles in the sky. Does the size of the particle matter? I mean, I would assume that the light, or the photons, would be more likely to hit large particles than small ones, but that would depend on just how many large particles there are compared to small ones. Surely our atmosphere is full of molecular nitrogen and oxygen, mostly, and they’d be vastly more numerous than large dust particles. Does size matter? And you say that blue light, or blue photons, tend to hit these particles because of their shorter wavelengths. I don’t quite get that. Why would something with a longer wavelength be more likely to miss? I think of, say, long arrows and short arrows. I see no reason why a longer arrow would tend to miss the target particles – not that they’re aiming for them – while shorter arrows hit and bounce off. And what makes them bounce off anyway?
Canto: OMG what a smart kid you are. And I think I can add more to those questions, such as why do we see different wavelengths of light as colours anyway, and why do we talk sometimes of waves and sometimes of particles called photons? But let’s start with the question of whether size matters. All I can say here is that it certainly does, but a fuller explanation would be beyond my capabilities. For a start, the particles hit by light are not only variable by size but by shape, and so potentially infinite in variability. Selected geometries of particles – for example spherical ones – can yield solutions as to light scattering based on the equations of Maxwell, but that doesn’t help much with random dust and ice particles. Rayleigh scattering deals with particles much smaller than the light’s wavelength but many particles are larger than the wavelength, and don’t forget light is a bunch of different wavelengths, striking a bunch of different sized and shaped particles.
Jacinta: Sounds horribly complex, and yet we get this clear blue sky. Are you ready to give up now?
Canto: Just about, but let me tackle this bouncing off thing. Of course this happens all the time, it’s called reflection. You see your reflection in the mirror because mirrors are designed as highly reflective surfaces.
Jacinta: Highly bounced-off. So what would a highly unreflective surface look like?
Canto: Well that would be something that lets all the light through without reflection or distortion, like the best pane of glass or pair of specs. You see the sky as blue because all these particles are absorbing and reflecting light at particular wavelengths. That’s how you see all colours. As to why things happen this way, OMG I’m getting a headache. The psychologist Thalma Lobel highlights the complexity of it all this way:
A physicist would tell you that colour has to do with the wavelength and frequency of the beams of light reflecting and scattering off a surface. An ophthalmologist would tell you that colour has to do with the anatomy of the perceiving eye and brain, that colour does not exist without a cornea for light to enter and colour-sensitive retinal cones for the light-waves to stimulate. A neurologist might tell you that colour is the electro-chemical result of nervous impulses processed in the occipital lobe in the rear of the brain and translated into optical information…
Jacinta: And none of these perspectives would contradict the others, it would all fit into the coherence theory of truth…
Canto: Not truth so much as explanation, which approaches truth maybe but never gets there, but the above quote gives a glimpse of how complex this matter of light and colour really is…
Jacinta: And just on the physics, I’ve looked at a few explanations online, and they don’t satisfy me.
Canto: Okay, I’m going to end with another quote, which I’m hoping may give you a little more satisfaction. This is from Live Science.
The blueness of the sky is the result of a particular type of scattering called Rayleigh scattering, which refers to the selective scattering of light off of particles that are no bigger than one-tenth the wavelength of the light.
Importantly, Rayleigh scattering is heavily dependent on the wavelength of light, with lower wavelength light being scattered most. In the lower atmosphere, tiny oxygen and nitrogen molecules scatter short-wavelength light, such as blue and violet light, to a far greater degree than long-wavelength light, such as red and yellow. In fact, the scattering of 400-nanometer light (violet) is 9.4 times greater than the scattering of 700-nm light (red).
Though the atmospheric particles scatter violet more than blue (450-nm light), the sky appears blue, because our eyes are more sensitive to blue light and because some of the violet light is absorbed in the upper atmosphere.
Jacinta: Yeah so that partially answers some of my questions… ‘selective scattering’, there’s something that needs unpacking for a start…
Canto: Well, keep asking questions, smart ones as well as dumb ones…
Jacinta: Hey, there are no dumb questions. Especially from me. Remember this is supposed to be science for dummies, not science by dummies.
Canto: Okay then. So maybe we should quit now, before we’re found out…
References:
‘Why is the sky blue?’, from 50 shades of grey matter, Karl Kruszelnicki, pp15-19
‘Blue skies smiling at me: why the sky is blue’, from Bad astronomy, Philip Plait, pp39-47
http://www.livescience.com/32511-why-is-the-sky-blue.html
Proxima b
Quote of the day/week/month/post:
Better to have questions you can’t answer than answers you can’t question – Max Tegmark (and many others)
Jacinta: So while astrophysicists argue over the likelihood of life elsewhere in our tiny but massive universe, some are focusing on our nearest star neighbour. Some wobbling of the red dwarf known as Proxima Centauri has revealed, upon lengthy observation, that it has a closely orbiting planet, which considering the relative coolness of the star – way too dim to be seen with the naked eye – and the proximity of its satellite, is very much in the habitable zone. While it’s too early to say so much for the naysayers, the discovery of a planet in the Goldilocks zone of our nearest star in a galaxy of billions of possibilities must surely raise hopes and expectations of life abundant.
Canto: This closest possible exoplanet was only discovered in August this year, so we’re desperate to find out more about it. Being in the habzone is one thing, habitability is another. Obvious questions we have no current way of answering are: does it have an atmosphere? Any possibility of water? Is it tidally locked? And of course we’d love to know if we could launch some sort of robotic mission to our nearest star neighbour. Meanwhile is there any other way of gleaning more info from this tantalising object?
Jacinta: It’s not likely to be habitable though. Solar winds are estimated to be some 2000 times those experienced on Earth, though we can’t be too sure. Researchers are trying to work out the size of the planet…
Canto: How do they know about those solar winds?
Jacinta: Oooh, that’s a horribly good question. It’s due to the closeness of the orbit, where you would expect the solar winds to be much stronger, as they are in our solar system. It’s believed that Mercury’s magnetic field, which should be stronger than it’s been measured to be because of its heavy metallic core, is dampened massively by our solar wind. So basically they would’ve inferred Proxima Centauri’s wind by our own. As to how they came up with the figure of 2000 times that experienced on Earth, I’ve no idea, but strong solar winds make it hard to maintain an atmosphere, which is vital for life. You’ve also talked about tidal locking, which is a feature of close orbits, such as the Moon’s orbit of the Earth. So you’ll have a permanently hot day side and a permanently cool night side, and this can be problematic for the creation of an atmosphere, according to modelling.
Canto: Now, all of this sounds very negative, but basing exo-planetary activity on what’s been the case, as far as we can work it out, in our solar system, has been really problematic hasn’t it?
Jacinta: Definitely, that’s why we need to go beyond modelling, if we can, and collect some real data. So we’re looking to the James Webb Space Telescope (JWST), the very exciting successor to Hubble to be launched around November 2018, to garner more info, which it’ll be perfectly equipped to do.
Canto: If by some near-miraculous combination of circs there is an atmosphere on Proxima b, or a reasonable quantity of liquid water, that would help distribute the heat around the planet. With no atmosphere, the difference between day side and night side would be stark.
Jacinta: Exactly, and that’s what the JWST should be able to detect, as the best way to detect the atmosphere is to measure the planet’s infrared heat signature. If the JWST finds a decisive and fixed difference between the planet’s day and night sides, it’s a safe bet that no atmosphere is present. The JWST will be equipped to measure this IR signature on both sides of the planet, and if it doesn’t find that stark difference, that’ll be when we can start speculating about an atmosphere and its constituents.
Canto: Though of course they’ve already started with the speculation. But really, whatever they find – and I don’t expect that everything will line up for life – the fact that we’ve found an exoplanet well worth investigating on the nearest star outside our solar system, with billions of stars yet to be homed in on, one by one – doesn’t that say something to those who argue for the Fermi paradox – where are they? Okay, Fermi and Hart were talking about intelligent life, and that may well be orders of magnitude more difficult to develop than life itself, but I’m sure that Fermi would be unsettled in his skepticism, if he was alive today, by the vast numbers of exoplanets, in other words possibilities for life, we’re discovering now, with so many to come in the near future.
Jacinta: Yes, bliss in this time it is to be alive, but to be young, that would be very heaven!
Cosmos issue 71, pp9-10
http://www.gizmodo.com.au/2016/08/how-well-get-our-first-big-clue-about-life-on-proxima-b/
en.wikipedia.org/wiki/Proxima_Centauri_b
How on earth? A chat about origins.
one impression of our proto-sun and solar nebula
Jacinta: I’d like to know how we got in this position.
Canto: What position?
Jacinta: Here, on Earth.
Canto: We?
Jacinta: Humans.
Canto: That’s a very long story, which I suspect nobody’s really qualified to tell. But maybe we can report on the best speculations. First, in order to understand how we got here we have to understand how the Earth got here.
Jacinta: And so on, infinitely regressing. So let’s just start with the Earth.
Canto: Needless to say we don’t know all the details and there are doubtless competing theories, and new data is being regularly uncovered, but it obviously has to do with how our entire solar system was formed.
Jacinta: I’ve heard that all the heavy metals like iron and whatnot are forged within stars, like when they go supernova, but our star hasn’t done that, all it seems to produce is light, yet Earth is full of heavy elements. I really don’t get it.
Canto: I recall reading years ago a theory that the Earth was formed from an accretion of planetesimals, little planets…
Jacinta: Planettes?
Canto: Yes, but how those little things came into being themselves I’m not sure.
Jacinta: Well we have lots of rocky bits and bobs called asteroids floating about in the solar system…
Canto: Yes, but not randomly. there’s a whole big asteroid belt between Jupiter and Mars, where they’re coralled, sort of.
Jacinta: But comets are different, they seem to have their individual eccentric orbits.
Canto: I suppose the point is that they also have heavy elements, and how were those elements formed?
Jacinta: Heat and pressure, I’m guessing, so things must’ve been hugely different in earlier times.
Canto: Well, this BBC site gives us some of the latest speculations. They reckon that the Earth probably formed from planetesimals, so that’s still the best hypothesis it seems, though it’s very light on details:
The Earth is thought to have been formed about 4.6 billion years ago by collisions in the giant disc-shaped cloud of material that also formed the Sun. Gravity slowly gathered this gas and dust together into clumps that became asteroids and small early planets called planetesimals.
Jacinta: Yes, that’s extremely vague. How do they know there was a disc-shaped cloud here? How can they investigate that far back?
Canto: Well don’t forget that looking out over huge distances means looking back in time.
Jacinta: Yes but a huge distance away isn’t here. Is it?
Canto: Well it might be here then.
Jacinta: Effing Einstein. But they’re also searching for extra data on the past, like checking out meteorites, which might contain material older than anything on Earth. Can they reliably date material that’s say, 5 billion years old? The Earth’s only about 4.5 billion years old, right?
Canto: I think 4.6 billion, give or take a few minutes. About a third of the age of the universe. And here’s the thing, we’ve dated all the meteorites and asteroids we can get to and they’re all round the same age, within a narrow range of a few hundred million years. So our date for the beginnings of the solar system is the oldest date for these floating and landing rocks, which is also our date for the Earth, about 4.6 billion.
Jacinta: So is our dating system completely accurate, and what by the way are carbonaceous chondrites?
Canto: Well, yes, radioactive decay provides a very accurate clock, and these meteorites have radioactive material in them, just as the core of our planet does. All the evidence so far suggests that things happened very quickly, in terms of accretion and formation of planets, once all this heavy and radioactive material was created. Carbonaceous chondrites are a type of meteorite. They’re amongst the oldest meteorites but relatively rare – they make up less than 5% of our meteorites. I mean the ones that land here. Why do you ask?
Jacinta: I’ve heard about them as being somehow important for research, and maybe dating?
Canto: Well there are different types of C chondrites as they’re called, and some of them, most interesting to us of course, are rich in organic compounds and water. This fact apparently shows that they haven’t been subjected to high temperatures, unlike for example the early Earth. But let me return to that BBC quote above. The theory goes that a supernova explosion, or maybe more than one, created all the heavy elements we have now – iron, carbon, silver, gold, uranium and all the rest, heat and pressure as you say, and these elements swirled around but were gravitationally attracted to a centre, which evolved into our sun. This was the spinning disc-shaped cloud mentioned above, known as the solar nebula.
Jacinta: Would you call that a theory, or a hypothesis, or wild desperate speculation?
Canto: I’d call it ‘the best we can do at the present moment’. But be patient, it’s a great time to be young in astronomy today. What we need is data, data, data, and we’re just starting to collect more data than we can rightly deal with on planets within and especially outside our solar system. Kepler’s just the beginning, girlie.
Jacinta: Je suis tout à fait d’accord, boyo. I think many of the astrophysicists are looking forward to having their cherished models swept aside by all the new telescopes and spectroscopes and what else and the data they spew back to Earth.
Canto: Uhh, well anyway let’s get back to our ‘best scenario for the moment’ scenario. So you have all this matter spinning around and the force of gravity causes accretion. It’s a messy scenario actually because everything’s moving at different velocities and angular momentums if that’s a thing, upwards, forwards, sideways down, and sometimes there’s accretion, sometimes fragmentation, but overall the movement is towards coalescence due to gravity. Particles grow to the size of monuments and then different sized planetesimals, fewer and bigger and farther between. And the smaller, gaseous elements are swept out by the solar wind into the great beyond, where they accrete into gas giants.
Jacinta: Right, but isn’t the data from Kepler and elsewhere already starting to play havoc with this scenario? Gas giants within spitting distance of their suns and the like?
Canto: Well, you need liquid to spit, but maybe you have a point, but I think it’s wise not to be too distracted by exoplanets and their systems at this stage. I think we need to find an internally coherent and consistent account of our own system.
Jacinta: What about the Juno probe, will that help?
Canto: Well I’m sure it will help us learn more about gas giants, but let’s just focus on the Earth now.
Jacinta: Okay, stay focussed.
Canto: These larger planetesimals became bigger gravitational attractors, each accumulating matter until we had four rocky planets in different, sufficiently distant orbits around their sun.
Jacinta: Oh yes, and what about the moons? Why didn’t they coalesce as neatly as all the other minor rocky bits?
Canto: Mmmm, well there’s nothing neat about all this, but mmmm…
Jacinta: How many moons are there?
Canto: For the inner planets? Only three, ours and two for Mars. So the question is, how come some of those rocks, or at least three, didn’t get stuck to the bigger rocks i.e. planets, via gravity, but instead started circling those planets, also due to gravity.
Jacinta: Yes, which might be the same question as why do the planets orbit around this massive gravitational attractor, the sun, instead of getting sucked into it, like what happens with those supermassive supersucking black holes?
Canto: Well first let me talk about our moon, because the most currently accepted theory about how our moon came into existence might surprise you.
Jacinta: It was a lot closer to the Earth at the beginning, wasn’t it? So it’s slowly spiralling away from us?
schematic of tidal forces affecting moon’s orbit and earth’s rotation
Canto: Yes. Tidal forces. The moon’s tidally locked to the Earth, it’s the same face she shows us always, but let’s keep on track, it was formed in the very early days, when things were still very chaotic. A pretty large planetesimal, or planetoid, slammed into Earth, which was somewhat smaller then, and it stuck to it and coalesced with it – the Earth was pretty-well molten in those days – and a lot of debris was thrown out into space, but this debris didn’t quite escape Earth’s gravitational field, instead it coalesced to form our moon. This theory was first put forward a few decades ago, after moon rocks brought back from the Apollo missions were found to be younger than the oldest Earth rocks, and composed of much the same stuff, which came as a great surprise. But now the theory is well accepted, as it accounts for a number of other factors in the relationship between the two bodies.
the hypothesised Thea impact, which enlarged the Earth and created the Moon
Jacinta: Okay, so is that it on how the Earth was formed?
Canto: Well, yes, but the bigger question is your original one – how did we get here. And that means we have to look at how life got started here. Because we’re only up to about 4.5 billion years ago – with the moon being formed about 50 million years after the Earth. And at that point the Earth was like a sea of hot magma, hot from all the collisions on the surface, and hot from the radiation bursting out from its core. Hardly great conditions for life.
Jacinta: Well there might’ve been life, but not as we know it boyo.
Canto: I’m skeptical, but we’ll talk about that next time.
Some sources:
on the relation between moon and earth
the solar nebula theory and its problems
exoplanets – an introduction of sorts
Jacinta: So do you think we’ve hauled ourselves out of ignorance sufficiently to have a halfway stimulating discussion on exoplanets?
Canto: I think we should try, since it’s one of the most exciting and rapidly developing fields of inquiry at the moment.
Jacinta: And that’s saying something, what with microbiomes, homo naledi, nanobots and quantum biology…
Canto: Yes, enough to keep us chatting semi-ignorantly to the end of days. But let’s try to enlighten each other on exoplanets…
Jacinta: Extra solar planets, planets orbiting other stars, the first of which was discovered just over 20 years ago, and now, thanks largely to the Kepler Space Observatory, we’ve discovered thousands, and future missions, using TESS and the James Webb telescope, will uncover megatonnes more.
Canto: Yes, and you know, about the Kepler scope, l was blown away – this might be veering off topic a bit, but I was blown away in researching this by the fact that Kepler orbits the sun. I mean, I knew it was a space telescope, but I just assumed it was in orbit around earth, probably at a great distance to avoid interference from our atmosphere, but that we can position satellites in orbit around the sun, that really sort of stunned me, more I think than the exoplanet discoveries. Am I being naive?
Jacinta: No, not at all. Well, yes and no. Everything is stunning if you haven’t followed the incremental steps along the knowledge pathway. I mean, if you think, hey the sun’s a way away, and it’s really big and dangerous, best not go there, or something like that, you might be shocked, but think about it, we’ve been sending satellites around the earth for a long time now, and we know how to do it because we know about earth’s gravitational field and can calculate precisely how to harness it for satellite navigation. We’ve currently got a couple of thousand human-made satellites orbiting the earth and trying more or less successfully to avoid colliding with each other. So the sun also has a gravitational field and we’ve known the mathematics of gravitational fields since Newton. It’s the same formula for a star, a planet or whatever, all you need to know is its mass and its radius. And look at all the natural objects orbiting the sun without a problem. Can’t be that hard.
Canto: Okay… so how do we know the mass of the sun? Okay, forget it, let’s get back to exoplanets. What’s the big fuss here? Why are we so dead keen on exploring exoplanets?
Jacinta: Well the most obvious reason for the fuss is SETI, the search for extra-terrestrial intelligence, but to me it’s just satisfying a general curiosity, or you might say a many-faceted curiosity. And it’s all about us mostly. For example, is the solar system that we inhabit typical? We’ve mostly thought it was but we didn’t have anything to compare it with, but now we’re discovering all sorts of weird and wonderful planetary systems, and star systems, with gas giants like Jupiter orbiting incredibly close to their stars – it’s completely overturned our understanding of how planets exist and are formed, and that’s fantastically exciting.
Canto: So you say we discovered the first exoplanet about 20 years ago, and now we know about thousands – that’s a pretty huge expansion of our knowledge, so how come things have changed so fast? You’ve mentioned new technologies, new space probes, why have they suddenly become so successful?
Jacinta: Well I suppose it’s been a convergence of developments, but let’s go back to that first discovery, back in 1992. Two planets, the first ever discovered, were found orbiting a pulsar – a rapidly rotating neutron star. First discovery, first surprise. Pulsars with planets orbiting them, who would’ve thought? Pulsars are the remnants of supernovae – how could planets have survived that? But that first discovery was largely a consequence of our ability to measure, and the fact that pulsars pulse with extreme regularity. Any anomaly in the pulsing would be cause for further investigation, and that’s how the planets were found, and later independently confirmed. Now this was big news, in a field that was already becoming alert to the possibility of exoplanets, so you could say it opened the floodgates.
Canto: Really? But they didn’t discover any more for two or three years.
Jacinta: Well, okay it opened the gates but it didn’t start the flood, that really happened with the second discovery, the first discovery of a planet orbiting a main-sequence star like ours.
Canto: Main sequence? Please explain?
Jacinta: Well these are stars in a stable state, a state of balance or equilibrium, fusioning hydrogen – basically stars not too different from our own, within much the same range in terms of mass and luminosity. So 51 pegasus b was the first planet to be discovered by the radial velocity method, and radial velocity means the speed at which a star is moving towards or away from us. We can measure this, and whether the star is accelerating or decelerating in its movement, by means of the Doppler effect – waves bunch up when the object emitting them is moving towards us, they spread out when the object is receding from us, and the degree of the bunching or the spreading is a measure of their speed and whether it’s accelerating or decelerating. Now we can measure this with extreme accuracy using spectrometers, and that includes any perturbations in the star’s movement caused by orbiting bodies. That’s how 51 pegasus b was discovered.
Canto: So… how long have we had these spectrometers? Were they first developed in the nineties, or to the level of accuracy that they could detect these perturbations?
Jacinta: Well I don’t have a precise answer to that apart from the general observation that spectroscopes are getting better, and more carefully targeted for specific purposes. The French ELODIE spectrograph, for example, which was used to find 51 pegasus b, was first deployed in 1993 specifically for exoplanet searching, and since then it’s been replaced by another improved instrument, but of the same type. So it’s a kind of non-vicious circle, research leads to new technology which leads to new research and so on.
Canto: So – we’ve gotten very good at measuring perturbations in a star’s regular movements…
Jacinta: Regular perturbations.
Canto: And we know somehow that these are caused by planets orbiting around them? How do we know this?
Jacinta: Well we will know from the size of the perturbation and its regularity that it’s an orbiting body, and we know it’s not a star because it’s not emitting any light (though it may be a low-mass star whose light isn’t easily separated from its parent star). We also know – we knew from the results that it was a massive planet orbiting very close to its star – a hot Jupiter as they call it. And that was another surprise, but we’ve developed different techniques for discovering these things and we often use them to back each other up, to confirm or disconfirm previous findings. The ELODIE observation of 51 pegasus b was confirmed within a week of its announcement by another instrument, the Hamilton spectrograph in California. So there’s a lot of confirmation going on to weed out false positives.
Canto: So radial velocity is one technique, and obviously a very successful one as it got everyone excited about exoplanets, but what others are there, and which are the most successful and promising?
Jacinta: Well the radial velocity method was initially the most successful as you say, and hundreds of exoplanets have been discovered that way, but this method actually led to a kind of bias in the findings, because it was only able to detect perturbations above a certain level, so it was best for finding large planets close to their stars. But of course that was good too because we had never imagined that large gassy planets could exist so close to their stars. It’s opened up the whole field of planet formation. Then again, if the main aim is to find earth-like planets, this method is less effective than other methods. So let’s move on to the Kepler project. Kepler was launched in 2009, and since then you could say it has blitzed the field in terms of exoplanet detection. It uses transit photometry, which means that it measures the dimming of the light from a star when an orbiting planet passes between it and the Kepler detector.
Canto: So I get the idea of transit, as in the transit of venus, which we can see pretty clearly, but it’s amazing that we can detect transiting planets attached to stars so many light years away.
Jacinta: Well this is how we’ve expanded our world, from the infinitesimally small to the unfathomably large, from multiple billions of years to femtoseconds and beyond, through continuously refining technology, but let’s get back to Kepler. It orbits around the sun, and has collected data from around 145,000 main sequence stars in a fixed field of view – stars that are generally around the same distance from that dirty big black hole at the centre of our galaxy as our sun is.
Canto: Is that significant – that we’re focusing on stars in that range?
Jacinta: Apparently so, at least according to the Rare Earth Hypothesis, which puts all sorts of unimaginative limits on the likelihood of earth-like planets, IMHO, but no matter, it’s still a vast selection of stars, and we’ve reaped a grand harvest of planets from them – some 3000-odd, with over 1000 confirmed.
Canto: So… promising earth-like planets?
Jacinta: Yes, but I must point out that earth-like planets are difficult to detect. You see, Kepler was a kind of experiment, and we’ve learned from it, so that our next project will be much improved. For various reasons due to the photometric precision of the instrument, and inaccurate estimates of the variability of the stars in the field of view, we found that we needed to observe more transits to be sure we’d detected something. In other words we needed a longer mission than we’d planned for. And of course, Kepler has suffered serious technical problems, especially the failure of two reaction wheels, which have affected our ability to repoint the instrument. Having said that, we’ve been more than happy with its success.
Canto: Okay I just want to talk about these exoplanets. Can you summarise the most interesting discoveries?
Jacinta: Well, Kepler has certainly corrected the view we might’ve gotten from the earlier radial velocity method that large Jupiter-like planets are more common than smaller ones. We’ve had a number of reports from the Kepler group over the years, and over time they’ve adjusted downwards the average mass of the planets detected. And yes, they’ve discovered a number of planets in the ‘habzone’ as they call it. But that’s not all – only this year NASA confirmed the existence of five rocky planets, smaller than earth, orbiting a star that’s over 11 billion years old. I’m just trying to give you an idea of the explosion of findings, whether or not these planets contain life. And we’ve only just begun our hunt, and the refinement of instruments. It’s surely a great time to study astrophysics. It’s not just SETI, it’s about the incredible diversity of star systems, and working out where we fit into all this diversity.
Canto: Okay, I can see this an appropriately massive subject. Maybe we can revisit it from time to time?
Jacinta: Absolutely.
Some very useful sites:
http://www.planetary.org/explore/space-topics/exoplanets/
https://en.wikipedia.org/wiki/Kepler_(spacecraft)