The science behind this year’s blood moons

Well, the first ‘blood moon’ of 2014’s come and gone. I missed it – the night sky where I live was socked in with 10/10 overcast at an altitude of about 200 metres.

US Navy photo of a total lunar eclipse in 2004, by Photographer's Mate 2nd Class Scott Taylor. Public domain, via Wikipedia.

US Navy photo of a total lunar eclipse in 2004, by Photographer’s Mate 2nd Class Scott Taylor. Public domain, via Wikipedia.

Still, I’ll have another chance on 8 October. And another on 4 April 2015. And a fourth on 28 September that year.

Although unusual, it’s not a unique occurrence to have four eclipses in quick succession. Technically they’re known as a tetrad.

The reason why eclipses are a bit erratic is interesting. A lunar eclipse is simple enough – the Moon passes through the shadow of the Earth. The reason lunar eclipses don’t happen every 27 days, as the Moon orbits the Earth, is because the Moon doesn’t always pass through the shadow when it’s ‘behind’ the Earth relative to the sun. It would if everything was lined up flat on the same plane – but it isn’t.

In fact, the Moon’s orbit is tilted relative to the ecliptic – the plane in which Earth and Sun orbit. The tilt varies between 4.99 and 5.30 degrees. The two points at which the orbit intersects the ecliptic are known as ‘nodes’, and they move around the Moon’s orbital path – technically, ‘precess’ – at a rate of  19.3549° annually.

For an eclipse to occur, the node (‘ascending’ or ‘descending’) has to coincide with the point where the Moon would pass through Earth’s shadow (which is on the ecliptic). That happens every 173.3 days. An eclipse is possible at that time, though again, the orbital mechanics don’t always mesh exactly.  There are more factors than just ecliptic and orbital angle. Earth’s shadow has a dense part (umbra) and a less dense part (penumbra). Sometimes there is only a partial eclipse. Sometimes it’s total.

Colour photo of the Moon taken by the Galileo probe in 1990 - a view we never see from Earth. The - uh - 'dark side' is to the left, fully illuminated. NASA, JPL, public domain.

Colour photo of the Moon taken by the Galileo probe in 1990 – a view we never see from Earth. The – uh – ‘dark side’ is to the left, fully illuminated. NASA, JPL, public domain.

The interlocking mechanisms of orbital mechanics – the way Earth, Sun and Moon all move in a complex dance of planes, angles and distances – means we end up with circumstance where strings of lunar eclipses – like the current tetrad – cluster. Between 1600 and 1900, for instance, there were no tetrads. But this coming century, there will be 8 of them.

So why red? The answer is one of the reasons why science is so cool. If you were standing on the Moon during a lunar eclipse, you’d see the Earth as a dark circle rimmed with fire – the light of every sunset and sunrise happening on Earth, all at once.

It’s red because of Rayleigh scattering – the way that the atmosphere scatters particular frequencies of light. I won’t repeat the explanation here – check out my earlier post.  Suffice to say, when sunlight passes through a horizontal thickness of atmosphere, the red wavelengths are what emerge – and those red light wavelengths refract into the shadow of Earth, lighting the Moon in blood-red hues.

So when you see a ‘blood moon’, what you’re actually seeing is the reflected light of every sunrise and sunset on Earth, all at once.

And that, my friends, is the really neat thing about those eclipses. Harbingers of doom? To me it’s cool science, on so many levels.

Copyright © Matthew Wright 2014


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The Big Bang theory wins again. So does Einstein.

It’s a great time to be a geek. We’re learning all sorts of extreme stuff. There’s a team led by John Kovac, from the Harvard-Smithsonian Center for Astrophysics, who’ve been beavering away on one of the fundamental questions of modern cosmology. The secret has demanded some extreme research in an extreme place. Antarctica. There’s a telescope there, BICEP2, that’s been collecting data on the cosmic background temperature. Last week, the team published their initial results.

Timeline of the universe - with the Wilkinson Microwave Antisotropy Probe at the end. Click to enlarge. Public domain, NASA.

Timeline of the universe – with the Wilkinson Microwave Antisotropy Probe at the end. Click to enlarge. Public domain, NASA.

The theory they were testing is as extreme as such things get and goes like this. Straight after the Big Bang, the universe was miniscule and very hot. Then it expanded – unbelievably fast in the first few trillionth trillionths of a second, but then much more slowly. After a while it was cool enough for the particles we know and love today to be formed. This ‘recombination’ epoch occurred perhaps 380,000 years after the Big Bang. One of the outcomes was that photons were released from the plasma fog – physicists call this ‘photon decoupling’.

What couldn’t quite be proven was that the early rate of expansion – ‘inflation’ – had been very high.

But now it has. And the method combines the very best of cool and of geek. This early universe can still be seen, out at the edge of visibility. That initial photon release is called the ‘cosmic microwave background’ (CMB), first predicted in 1948 by Ralph Alpher and others, and observed in 1965 by accident when it interfered with the reception of a radio being built in Bell Laboratories. That started a flurry of research. Its temperature is around 2.725 degrees kelvin, a shade above absolute zero. It’s that temperature because it’s been red-shifted (the wavelengths radiated from it have stretched, because the universe is expanding, and stuff further away gets stretched more). The equation works backwards from today’s CMB temperature, 2.725 degrees Kelvin, thus: Tr = 2.725(1 + z).

The COBE satellite map of the CMB. NASA, public domain, via Wikipedia.

The COBE anisotropic satellite map of the CMB. NASA, public domain, via Wikipedia.

The thing is that, way back – we’re talking 13.8 billion years – the universe was a tiny fraction of its current size, and the components were much closer together. Imagine a deflated balloon. Splat paint across the balloon. Now inflate the balloon. See how the paint splats move further apart from each other? But they’re still the original pattern of the splat. In the same sort of way, the CMB background pattern is a snapshot of the way the universe was when ‘photon decoupling’ occurred. It’s crucial to proving the Big Bang theory. It’s long been known that the background is largely homogenous (proving that it was once all in close proximity) but carries tiny irregularities in the pattern (anisotropy). What the BICEP2 team discovered is that the variations are polarised in a swirling pattern, a so-called B-mode.

The reason the radiation is polarised that way is because early inflation was faster than light-speed, and the gravity waves within it were stretched, rippling the fabric of space-time in a particular way and creating the swirls. Discovering the swirls, in short, identifies both the early rate of expansion (which took the universe from a nanometer to 250,000,0000 light years diameter in 0.00000000000000000000000000000001 of a second…I think I counted right…) and gives us an indirect view of gravitational waves for the first time. How cool is that?

Albert Einstein lecturing in 1921 - after he'd published both the Special and General Theories of Relativity. Public domain, via Wikimedia Commons.

Albert Einstein lecturing in 1921 – after he’d published both the Special and General Theories of Relativity. Public domain, via Wikimedia Commons.

What’s a ‘gravitational wave’? They were first predicted nearly a century ago by Albert Einstein, whose General Theory of Relativity’of 1917 was actually a theory of gravity. According to Einstein, space and time are an entwined ‘fabric’. Energy and mass (which, themselves, are the same thing) distort that fabric. Think of a thin rubber sheet (space-time), then drop a marble (mass/energy) into it. The marble will sink, stretching the sheet. Gravitational waves? Einstein’s theory made clear that these waves had to exist. They’re ripples in the fabric.

One of the outcomes of last week’s discovery is the implication that ‘multiverses’ exist. Another is that there is not only a particle to transmit gravity, a ‘graviton’, but also an ‘inflaton’ which pushes the universe apart. Theorists suspect that ‘inflatons’ have a half-life and they were prevalent only in the very early universe.

There’s more to come from this, including new questions. But one thing is certain. Einstein’s been proven right. Again.

Copyright © Matthew Wright 2014

Coming up: More geekery, fun writing tips, and more.

Into deepest time with the REAL big bang theory

My wife occasionally calls herself ‘Penny’, as in Penny off The Big Bang Theory. Especially when I get together with my mathematician friends and we talk geek.

I’m not sure which of us is meant to be Sheldon. Anyway, the ‘big bang’ theory itself was first proposed in 1927 by a Catholic priest, Monseigneur Georges Henri Joseph Édouard Lemaître (1894-1966). He was trying to explain Vesto Slipher’s discovery that distant galaxies were retreating. And he was ignored. Then, in 1929, Edwin Hubble (1889-1953) suggested the same thing. Like most academic fields, physics is all to do with in-crowds; when Hubble spoke, other physicists pricked up their ears.

Timeline of the universe - with the Wilkinson Microwave Antisotropy Probe at the end. Click to enlarge. Public domain, NASA.

Timeline of the universe – with the Wilkinson Microwave Antisotropy Probe at the end. Click to enlarge. Public domain, NASA.

Their logic went like this. Distant galaxies appear redder than they should.  This is because the wavelengths of light and other electromagnetic emissions from them are being stretched from our perspective, meaning they must be moving away. This effect was first discovered by Ernst Doppler who realised this was why fast-moving vehicles go ‘neeeeoooww’. The sound waves are being stretched from the perspective of a stationary listener as the source moves away, so to them the pitch appears to drop. (You can buy a Sheldon costume so you can be the Doppler Effect, like he was in Series 1 Ep. 6…here.)

It works the same with electromagnetic emissions, and red has a longer wavelength than other visible light, so things moving away appear redder to us. Hence the term ‘red shift. It’s used to describe the phenomenon, even if the wavelength isn’t visible light. (No costumes for this one).

Hubble discovered not only that distant galaxies retreat from us, but that the further away they are, the faster they retreat. Hubble’s Law followed: v = H0D, where v is velocity of recession, Ho is Hubble’s constant, and D is the proper distance. The value for Hubble’s constant has never been agreed, but recent work suggests it might be 71 +/- 7 km/sec per megaparsec. Probably. A bit.

It also turned out that distant galaxies are moving away from us whichever way we look, showing that space-time itself is expanding. Imagine a rubber balloon with equidistant dots on it. Inflate the balloon. The dots move apart equally – and the distant ones are moving away faster. That holds true for space-time.

The conclusion was that the universe had been smaller – a mathematical point, in fact, from which everything exploded into the reality we know and love today. Pretty much like the opening credits on The Big Bang Theory, in fact.

Of course, it wasn’t expansion into a void. It was an expansion of space-time itself. The very fabric of physical reality.

It was a kind of cool idea, but nobody had any way of proving it. Physicists argued over whether there had been a ‘big bang’, or whether the universe operated by a modified ‘steady state’ of constant but expanding existence. Then, in 1948, Ralph Alpher and Robert Herman predicted that we should be able to see cosmic background radiation from the ‘big bang’ – and it was found in 1965. The radiation has a black body (idealised) temperature of 2.72 degrees Kelvin, give or take a tad (I define +/- 0.00057 degrees as a ‘tad’).

Into deepest space: Hubble space telescope image of galaxies from the early universe. Public domain, NASA.

Into deepest space: Hubble Space Telescope image of galaxies from the early universe. Public domain, NASA.

And you know the coolest part? Albert Einstein figured it all out in 1917, before any of the evidence was available. His General Theory of Relativity made clear the universe couldn’t be static – it had to be expanding or contracting. Einstein thought that had to be wrong, so he added a ‘cosmic constant’ to eliminate the expansion. But expansion was true, and he later admitted the ‘constant’ fudge was a mistake. His original equations held good.

Einstein had, in short, figured out how the universe worked – so completely that his theory explained the bits that hadn’t been discovered yet.

How cool is that?

Copyright © Matthew Wright 2013

Coming up soon: ‘Write it now’ and ‘Sixty Second Writing tips’, more humour, more science…and, more.

Totally mind-blown by ‘Gravity’ and its real physics

The other weekend I went to see Gravity, in 3D. As we left the cinema there was only one thing I could say to my wife. ‘That was f—-ing AMAZING.’

Gemini 7 from Gemini 7, 15 December 1965. NASA, public domain, via Wikipedia.

Gemini 7 from Gemini 6, 15 December 1965. NASA, public domain, via Wikipedia.

I use that word a lot, just not usually on this blog. But the intensifier’s apt. After weeks slating dumb movie physics (and more to come) I was gob-smacked. Alfonso Cuaron, Kevin Grazier and the team made a massive effort to reproduce free fall. Free fall? Absolutely. It’s not ‘weightlessness’, and the astronauts are not ‘beyond the pull of Earth’s gravity’. Not in low orbit. It’s ‘free fall’ – as in falling and missing the ground. That’s what orbiting is. Seriously. Wanna see the math?

They should also have called the movie ‘Conservation of Angular Momentum’, because that’s what the physics were – everything spun…and kept spinning, because there was no force to stop the spin… Coool.

Agena target vehicle photographed from Gemini 11. Public domain, NASA, via Wikipedia.

Agena target vehicle from Gemini 11. Public domain, NASA, via Wikipedia.

Then there was the gorgeous imagery. I felt like I’d been transported back to the National Geographics I read as a kid – wonderful glossy Kodachromes of Gemini missions with Earth floating blue and magical behind them.

All that’s overlaid by the story –  an edge-of-the-seat tension drama.  Sandra Bullock’s character was tremendous. Ever wondered what you might do in a life-or-death situation? Go to pieces? Or decide to do whatever has to be done to stay alive – even if it means dying in the attempt? She took us on that decision and journey. Damn it was good!

I think the minor reality compromises the makers made to tell the story didn’t compromise suspension of disbelief. This was an awesome movie.

Of course, I’m going to list a few of those compromises – along with ways the movie also showed up the reality. But that includes spoilers – so if you haven’t seen the movie, go see it – trust me, you WANT to see this one! Then read the rest of this post.

I’ll separate the spoilers with this photo of the real thing – which is what the movie looked like. You can see my house, adjacent to the lower box on the aerial.

Spacewalk to assemble the ISS, 12 December 2006. New Zealand is below - North Island to the right, South to the left. My house is directly under the aerial centre-frame. Photo: NASA, public domain, via Wikipedia.

Spacewalk to assemble the ISS, 12 December 2006. New Zealand is below – North Island to the right, South to the left. Photo: NASA, public domain, via Wikipedia.

So – the compromises. [Spoiler Alert!] There was the scene where Bullock had to let Clooney drift. In fact they were already stopped; she had merely to tug on the cable with her pinkie finger, and he’d have drifted slowly towards her. Then there’s flying from one satellite to another using only an MMU (Manned Manoeuvering Unit) back-pack, which was flown for real in 1984 and then retired.  Hubble and the International Space Station (ISS) orbit in different planes - different angles relative to the equator – which takes a lot of energy to alter. Not possible even with a fully fuelled MMU, which has velocity-change capability (‘delta-V’) of 24.4 metres per second. There are also the physics of rendezvous in space, which are counter-intuitive – you don’t fly from place to place like the movie. I believe the original expert on how it’s done for real is Buzz Aldrin.

[Spoiler alert!] Spacesuits are harder to take on and off than portrayed, and the underwear isn’t lycra – it’s nappies (diapers), cotton long johns, and a liquid-cooling garment. Here’s a video. Actual donning time is about 20 minutes. There’s a pressure differential; the Extra Vehicular Mobility Unit (EMU) – NASA’s term for the spacesuit, which lacks any propulsion system – is pressurised to 4.3 PSI (222.37 torr), whereas the ISS operates at 14.7 PSI (760.2 torr). This means the astronauts have to spend four hours pre-breathing oxygen to avoid dysbarism – ‘the bends’, before a space-walk. Total time in the suit might be ten hours or more. That’s why the engineers insist on the nappy.

Gemini astronaut space-walking. Public domain, NASA, via Wikipedia.

Gemini astronaut space-walking. Public domain, NASA, via Wikipedia.

[Spoiler alert!] People don’t snap-freeze in vacuum. It is a brilliant insulator and heat is lost through radiation, not conduction. That’s why thermos flasks work. In shadow at Earth’s orbital distance it’s over 160 degrees C below, but that doesn’t alter the physics. The human body is more than half water, which has high thermal energy storage capacity (334 million joules per cubic metre). You’d freeze solid providing you stayed in that shadow, but not in minutes. Or hours…

And now the realities. Get this – a lot of the mayhem they showed has actually happened before, mostly to Soviet spacecraft. [Spoiler alerts!]

* Re-entry while tumbling. The Soyuz 1 mission tumbled into the atmosphere after failure of the control systems on the maiden flight of the Soyuz 7K-OK spacecraft, 24 April 1967. The sole cosmonaut, Vladimir Komarov, never gave up – he was a fantastic pilot, and managed to control the entry in the end. But the parachute release door was damaged. Komarov released the reserve chute, but it tangled with the drag chute and he was killed when Soyuz 1 slammed into the ground near Orenburg.

Soyuz TMA. Public domain, via Wikipedia.

Soyuz TMA. Public domain, via Wikipedia.

* Re-entry without PAO separation (Priborno-agregatniy otsek = service module). Only the SA re-entry module (‘B’ in the diagram) returns to Earth, base-end first; the other modules are jettisoned before re-entry. During the mission of Soyuz 5, 18 January 1969 – the orbital module (‘A’) jettisoned normally, but the PAO (‘C’) did not separate, causing the re-entry module to hit the atmosphere nose first with the PAO behind it. Oops. Luckily the bolts burned through and the PAO broke away, allowing the re-entry module to spin and present the heat shield to the atmosphere. It happened again with Soyuz TMA-10 on 21 October 2007, and AGAIN with Soyuz TMA-11 on 19 April 2008.

* Fire in orbit. On board Mir space station, 23 February 1997. It took 14 minutes to extinguish.

* Collision between spaceship and space station solar panel. Mir again, 25 June 1997 – the Progress M-30 freighter mowed through a solar panel on the Spektr module, colliding with the module and puncturing it.

* Spacecraft sinks on splash-down and the astronaut’s spacesuit fills with water. Happened to Gus Grissom on 21 July 1961 with Mercury-Redstone 4.

Damn, Gravity was a good movie!

Have you seen Gravity yet? What did you think of it?

Copyright © Matthew Wright 2013

Why is the sky blue? And other annoyingly rhetorical questions

I am often bemused by people who use ‘why is the sky blue’ as rhetoric – often to symbolise some question for which there is no answer.

Actually there is an answer, and we’ve known it since 1871: ‘Rayleigh scattering’. It’s also why sunsets look red and orange. The effect is named after John William Strutt, Third Baron Rayleigh (1842-1919), the British physicist who discovered it.

The phenomenon works like this: incoming sunlight, which contains light of all wavelengths and hence colours, is scattered by molecules in the upper atmosphere. The increasing density of atmosphere itself also acts as a scattering mechanism.  The wavelength of light mostly scattered (technically, absorbed and re-emitted) is at the shorter end – blue and green, creating the diffuse glow across the whole sky which, to the human eye, usually looks light blue.

Other wavelengths are scattered when the light comes at a direct angle, which is why the Sun appears yellow (but don’t look – it will damage your eyes).

This scattered light is also polarised. That’s why a polariser on your camera produces such a dark blue at certain viewing angles relative to the sun.

Oriental Bay - named after one of the original colony ships that arrived in 1840 and a popular walk for Wellingtonians today.

Oriental Bay, Wellington – an image I took with full polarising, creating false-colour blue in the sky.

When the sun angle lowers, and the light is passing through a thicker layer of atmosphere, more of the blue wavelengths are scattered and only the longer wavelengths are obvious – orange and red – hence the colours of sunset, gradiating to a darkening blue above.

Blue sunset on Mars - for the same reason skies are blue on Earth. An approximately true colour image by the Spirit rover at Gusev Crater, 2005. Photo: NASA/JPL, public domain.

Blue sunset on Mars – for the same reason skies are blue on Earth. An approximately true colour image by the Spirit rover at Gusev Crater, 2005. Photo: NASA/JPL, public domain.

This scattering effect is true everywhere – not just on Earth. It varies slightly because atmospheric compositions differ, and the oxygen in our atmosphere is a factor. However, if you were dangling from a balloon in Jupiter’s atmosphere and looked up, you’d see blue sky there, even though the air is mostly a poisonous mix of hydrogen, helium and traces of other stuff like phosphene. Even the sky of Mars is blue – we’ve imaged that blue slice-wise through the upper air. It appears pink from lower down, looking up, because suspended dust in the atmosphere scatters the longer wavelengths. That’s still Rayleigh scattering. And Martian sunsets are blue – for exactly the same reason.

Mars imaged in 1995 by the Hubble Space Telescope - with blue cast due to Rayleigh scattering. Cool. Photo: NASA, public domain.

Mars imaged in 1995 by the Hubble Space Telescope – with blue cast due to Rayleigh scattering. Cool. Photo: NASA, public domain.

Earth’s sky appears blue, I might add, to us. Humans are lucky; our colour vision is based on three receptors. Many animals use two, which reduces the palette of colours they can see. (Of course, most of them also have much better night vision: swings and roundabouts).

So there you have it. Next time anybody idly gets rhetorical and asks ‘why is the sky blue’, you can go all Sheldon on them with an annoying literal answer. Or talk about Martian sunset colours, but I suppose that comes to the same thing really.

Copyright © Matthew Wright 2013

Into the unknown beyond the edge of the solar system

This week’s news that Voyager 1 has left the solar system is pretty cool.

Voyager 1 launching, 5 September 1977. Photo: NASA, public domain.

Voyager 1 launch, 5 September 1977. Photo: NASA, public domain.

Actually, not just cool. Totally awesome.  JPL scientists were able to use Voyager’s ‘plasma wave’ instrument to measure oscillations in plasma around the probe, giving its density; and this week, the plasma science team at the University of Iowa analysed the data and confirmed that the probe had entered interstellar space.

The important part is what it means. For the first time in the 4.6 billion year history of our world, something from Earth has left the solar system.

It is the stuff of dreams.

Not bad for a space probe launched when trousers were flared and disco was in. The day was 5 September 1977. With its twin, Voyager 2, the 770kg probe was the low-budget reality of a ‘grand tour’ that fell victim to post-Apollo penury. And once their Titan-Centaur boosters had exhausted their fuel, the Voyagers were on a rail for the interstellar void. Both had gold records on board – not Bee Gees – recording human endeavour, should the probes ever be found some time.

Picture taken by Voyager 1 of Saturn - a view impossible from Earth, where we don't get that angle on the night side. Photo: NASA, public domain.

Picture by Voyager 1 of Saturn, November 1980 – a view impossible from Earth, where we don’t get that angle. Photo: NASA, public domain.

But both Voyagers were still up for major course changes for free. In the late 1970s, the four major planets – Jupiter, Saturn, Uranus and Neptune – were aligned in such a way that a probe could be lobbed from one to the other, using the gravitational field of each planet to bend the trajectory. Some of the momentum of each world was transferred to the probe, slowing the planet infintesimally, and radically altering the course of the Voyagers.

Voyager 2 flew past all four giant planets. But Voyager 1 encountered only Jupiter and Saturn. By taking a different trajectory, Voyager 1 could get a close look at Titan, Saturn’s largest and most enigmatic moon.

The courses and positions of four probes leaving the solar system, all launched in the 1970s. I made this with my handy Celestia installation - cool, free science package.

The courses and positions of four probes leaving the solar system. I made this with my handy Celestia installation.

That carried a cost. Voyager’s course was twisted out of the plane of the ecliptic, the narrow band in which the planets orbit the Sun. And now – 36 years and 18.6 billion kilometres after launch, Voyager 1 has passed through the heliopause – where the solar wind thrown off by the Sun meets the interstellar medium – and stops.

Voyager probes at the heliopause. Credit: NASA/JPL, public domain.

Voyager probes at the heliopause. Note how the heliopause is compressed, like a bow wave, in the direction the solar system travel as it orbits the galactic centre. Credit: NASA/JPL, public domain.

It’s unknown space. Although the Oort cloud and dwarf planets such as 90377 Sedna, have orbits that go beyond it, the heliopause is a practical line in the sand (well, in the vacuum) for scientific purposes.

Voyager 1 detected that the solar wind had dropped to zero in 2011, meaning it was approaching the border. It’s likely the probe crossed into the interstellar void in August 2012. Certainly it was well into the interstellar medium this year – some 125 times as far away from the Sun as Earth.

It’s worth remembering that these measurements involve detecting miniscule numbers of particles. Despite interesting artistic renderings like the one above,  both heliopause and interstellar medium are hard vacuum, with a density of one atom per cubic centimetre.

The practical mission of both Voyager probes will finish in a decade or so. They are each powered by three radioactive thermal generators, and those are dwindling. By 2025-30 there won’t be enough power to run even individual instruments.  But that won’t stop both hurtling onwards into deepest space until they hit something – or the universe ends, monuments to human endeavour that will last longer, perhaps than our own planet. In 40,000 years, Voyager 1 will come within 1.6 light years of the star Gliese 445 – an M-class dwarf star which, by then, will be a mere 3.45 light years from us. It’s coming towards us faster than Voyager 1′s heading for it.

The whole thing is pretty cool and amazing.

Copyright © Matthew Wright 2013


Is there life on Mars – again?

NASA has plans afoot to build a second nuclear powered Mars rover, Curiosity style, and land it on the planet in 2020 with another fireball-and-rocket crane spectacular.

Curiosity landingOnce there it will look directly for signs of ancient life, on the logic that there won’t be any to find easily today. But an older, wetter and more convivial Mars might have been a different story

The rover will even have a box for samples that might be returned to Earth by some later mission.

Which is pretty cool on just about every count. And maybe we’ll get answers to questions that have been burning since long before the dawn of the space age

Assuming, of course, we ask the right ones. That’s been the problem.  When the Vikings landed on Mars in 1976 they were geared to look for life-as-we-know it. The results were ambiguous and likely caused by the perchlorates that we now know saturate the upper layers of the Martian soil.

And therein lay the real issue. On Earth, if one experiment doesn’t work, you devise another and try that, based on what you learned the first time.

Not so easy when you have to transport that repeat experiment to Mars to a chorus of shrinking budgets, where ‘failure’ is likely to kill the next allocation – yet where you might have to follow your Mk II Life Detecting Lab with a third…and a fourth…

Part of the problem was that we didn’t know enough to ask the right questions. Viking’s ambiguous failure threw the issue back to basics. Had Mars even had water? Broadly, that’s where the focus has been since – and now that we have ‘yes’ to a lot of those basic questions, it’s possible to take the next steps.

To me this is a cool application of scientific method – systematically, over decades, and it’s paying dividends.

And we can speculate that even if Mars never had life – or if it did, and it’s gone extinct, it’s likely to have other life soon. Us. Maybe.

Your thoughts?

Copyright © Matthew Wright 2013

Forget Star Wars – here’s the real-life Death Star

It’s in a nebula with the boring name of NGC-3372, and the un-boring name of Homunculus, maybe 7,500 light years from Earth. It’s called Eta Carinae. But you might call it the Death Star.

Eta Carinae. NASA, public domain. Click to enlarge.

Eta Carinae. See that nebula? It’s NGC-3372, also called the Homunculus Nebula – one or two solar masses worth that erupted out of the star in 1843. NASA, public domain. Click to enlarge.

Luckily for us, it’s not pointed our way. We think.

It’s currently a million times more powerful than the Sun, but the output has fluctuated wildly in historic times, like a guttering candle. A major flare that started in 1843 lasted 20 years and made Eta Carinae the next brightest star in the sky after Sirius.

Eta Carinae is 872 times the distance of Sirius. That flare, alone, was as bright as a supernova.

Victorian-age astronomers looked and marvelled. But they didn’t really have the gear that we do. But get this – we can make up for that now. Some of that light was reflected off dust clouds about 85 light years beyond Eta Carinae, from Earth’s vantage point. That ‘echo’ bounced back, whipped past Eta Carinae – and is reaching us now. Let me say that again. We’re picking up light 170 years after we first saw it – by its reflection!  Scientifically, that’s sub-zero cool.

Today the gas blown off in that event appears as a nebula surrounding a blazing blue-white star roiling in pre-hypernova mode.

There are a couple of theories to explain how a hypernova works. Both likely true in different circumstance, but the one that counts is the ‘collapsar’ model. High-mass stars fuse hydrogen around their core at a phenomenal rate. After a while the star starts fusing helium into lithium, and so on up the periodic table until it reaches iron. That’s stable and can’t fuse. So it cools. And then – if the core has more mass Chandashekar’s Limit, extreme things happen, faster than any human could perceive.

Artists impression of a GRB. Zhang Whoosley, NASA, public domain, via Wikipedia.

Artists impression of a GRB. Zhang Whoosley, NASA, public domain, via Wikipedia.

First, the core of the star collapses at light-speed into a black hole. A reflected blast wave erupts at light-speed. The advancing wave intersects with the stellar matter to produce ultra-energetic radiation at gamma frequencies, focussed by the star’s magnetic field and squirted in a beam down its polar axes. Meanwhile, the main blast, following at a more sedate fraction of light-speed, rips the star apart with a glare that can out-shine whatever galaxy the star is inhabiting.

What’s gamma radiation? It’s at the sharp end of the electromagnetic spectrum. Frequencies start at 10,000,000,000,000,000,000 hertz and go up, which gives a gamma burst a wavelength smaller than the diameter of an atom. Gamma ray bursts are among the most energetic phenomena observed. We can detect them in galaxies billions of light years away.

If Eta Carinae blew and its GRB hit us, it’s been calculated that would deliver energy equivalent to one kiloton of TNT in energy for every square kilometre of the hemisphere facing the radiation. Ouch.

Probably it’s not pointed our way, but if Earth was hit by a  burst approaching that intensity, we’d know. A lot depends on energy and duration.  It is unlikely a burst would reach ground level; air is a shield against gamma and x-rays. But part could penetrate at ultraviolet frequencies and burn anybody under it.

The larger problem is gamma radiation hitting the upper atmosphere – smashing the ozone layer, at least. Potentially, a GRB could create nitrogen dioxide smog – plunging Earth into darkness. While this would occur only on the side  struck by the beam, high-altitude winds would spread the effects. And we’d get rain. Nitric acid rain. Here’s the paper analysing the biological effects.

The thing is, while we think Eta Carinae isn’t pointed at us, the Wolf-Rayet star WR-104 might be.

Do I lie away at night worrying? No. Gamma ray bursts are rare. Really big ones happen in the order of once every 100,000 years in the galaxy. Their effects occur in a cone spreading from the poles of the exploding star. The chance of one hitting Earth is remote.

Still, there is a theory that a GRB might have caused the Ordovician-Silurian extinction event about 450 million years ago. Another theory suggests a burst hit us in the eighth century – it didn’t have enough energy to smash everything, but may have caused climate change

Realistically, for us, there are more likely things that will knock off humanity.

Meanwhile, we can look up at the skies and marvel at the wonders of extreme physics we’re discovering…out there.

Copyright © Matthew Wright 2013

Sixty second writing tips: why we write

I saw the supermoon this week. It hung luminescent yellow in the low horizon.

From a scientific perspective, not too different from any full moon. But it was there, and it carried an emotion because it emerged in the first clear night sky we’d had over Wellington since the worst storm in years. And something struck me. Could I write about the emotions and mood it conveyed? Could I imagine how others might receive it, and write about them? Perhaps.

But also, maybe not.

I’ve spent over 40 years learning about writing and then doing it. I started when I was seven. I was formally trained in fiction writing. I’ve written every day I can since  forever – not just books in my academic field but also as a freelance journalist and writer.  Here’s my list. And I’ve done a lot of other work in the industry.

Yet from this experience I know that words are simply imperfect vehicles with which we try, as writers, to express the perfection of thoughts and concepts.

All too often I have the idea in my mind – and cannot translate that to the page to my satisfaction. The crystal perfection of concept, which cannot be conveyed by words.

The real skill of writing, I think, is the aspiration towards that end point  - which is unattainable. Naturally.

Yet we must try – and in that attempt, perhaps surprise ourselves. And our readers.

Your thoughts?

Copyright © Matthew Wright 2013

Why a supermoon is just, so, well, super

Last night the Moon shone big and bright. A supermoon.

A supermoon happens when the perigee point of the lunar orbit happens to fall at the point furthest away from the sun, so the Moon is fully illuminated as seen from Earth. A sketch I made with the help of Celestia and a drawing tool.

How a supermoon works.  The perigee isn’t always at this point – the alignment happens about every fourteen months. A sketch I made with Celestia and a drawing tool.

A ‘supermoon’ happens when the lunar perigee – the point at which it is closest to Earth – occurs on the side of Earth’s orbit furthest from the sun, which means the lunar disk is fully illuminated from Earth’s perspective. Hence we get a moon that not only has a visual diameter 12 percent greater than that of the Moon at apogee, but which is also full.

The difference isn’t huge. The Moon’s distance varies from about 405,000 to about 360,000 km from Earth.  It doesn’t add much to the tides – a few inches at most – and is a perfectly normal occurrence.

For me it highlights how unique our Moon is. No other planet in the solar system, except Pluto, has a moon that is such a large proportion of its own size. (Don’t get me started on Pluto’s demotion to ‘dwarf’ planet).

Current theory – devised mainly from Apollo data – suggests that the Moon formed about 4.5 billion years ago, and only 30-50 million years after the Solar System began coalescing, when an impactor the size of Mars  - ‘Theia’ – ploughed into the proto-Earth, probably on a slaunchwise angle.

The impact rendered both bodies fragmented and molten. The iron cores of both sank to the centre of the Earth – which is why Earth has such a large one compared to Mars or Venus – while the lighter material coalesced to form the Moon.

A variant explains how the Moon is two-faced – the far side (which gets just as much light as the near side, so we can’t call it ‘dark’) is very different from the side we see. Why? One theory suggests Earth emerged from the impact with two moons which, themselves, subsequently collided. Splat. Later, tidal effects meant that the heavier side – the one we see, with all the maria – ended up facing the Earth.

Which brings me to the last cool link between this supermoon and the history of the Earth-Moon system. Way back when, as the moon coalesced, it was only about 14,000 miles from Earth and both bodies were rotating far more rapidly than today.

Does the Moon rotate, you say? Actually, it does spin – it rotates once in exactly the same time as it takes to orbit the Earth. This outcome is known as ‘tidal locking’ and occurs when a small body – in the Moon’s case, 1/81 times the mass of Earth – orbits a larger one.

Colour photo of the Moon taken by the Galileo probe in 1990 - a view we never see from Earth. The - uh - 'dark side' is to the left, fully illuminated. NASA, JPL, public domain.

Colour photo of the Moon taken by the Galileo probe in 1990 – a view we never see from Earth. The – uh – ‘dark side’ is to the left, fully illuminated. NASA, JPL, public domain.

Each induces tides in the other, robbing each other of rotational energy. Naturally the larger body ‘wins’, though it’s also slowed in the process. The energy doesn’t vanish, of course. It’s turned partly into heat, and then radiated; but it also partly gets translated into orbital momentum.

What this means in practise is that the Moon moves away from the Earth. In about three billion years, it will be far enough away that it doesn’t stabilise the Earth’s axial tilt.

Can Earth ever be tidally locked to the Moon? Theoretically – yes, but apparently it’ll take 50 billion years. The orbital period of the Moon – and the length of our ‘day’ – would be about 47 of our existing days. But it won’t ever happen. Earth will be swallowed up by the Sun, as it turns into a red giant, well before then.

But that’s way off in the future, and I can guarantee humans won’t be around to see it. Unlike today’s supermoon.

Copyright © Matthew Wright 2013

Coming up this week: My take on Eta Carinae, more writing tips, and more.