I am one of 18-35% of the human population with a photic sneeze reflex! If I step out of a dark building into full bright sunlight, it makes me sneeze. It always has. When I was a kid, I used to think I was just weird somehow, but seemingly, it isn't so rare.

First documented in work attributed to Aristotle, solar sneezes are apparently a genetic thing. The nerve responsible for sneezes (believed to be the trigeminal nerve) has a close association in some people with the optic nerve. As a result, if you overstimulate your optic nerve (by suddenly stepping into bright sunlight, for instance) it also stimulates your trigeminal, making you sneeze. How curious.

I always seem to end up reading random things while I'm waiting for computers to come back online...

Water is all the rage. It gets mentioned in every single high profile space mission of late. Searching for water on Mars, water inside Europa, water in the atmospheres of exoplanets. Going to the Moon? Don't forget to check for water! All with good reason, of course. Being made of 72.8% water, it's rather important that wherever we might go in the Universe, we have a ready supply of it. But water's been found in some surprising places.

The Sun isn't the first place you'd expect to find water. At a temperature of around 6000°C, the Sun's photosphere is the nearest thing you'll find to an actual "surface" of our parent star. At such an immense temperature, the photosphere is a collection of gas and plasma which form into cells known as granules. With a lifetime of about 10 minutes, these granules bubble up from below the Sun's photosphere, before bursting like soap bubbles. Collossal soap bubbles. With an average diameter of one thousand kilometres, solar granules are typically about the size of Greenland.

6000°C is too hot for water to exist. At these temperatures the molecules simply split apart into hydrogen and hydroxyl (OH) radicals. But there are some slightly more hospitable spots on the Sun. Cooler spots. Sunspots.

Cool is a relative concept when you're talking about the surface of a star. At around 3500°C, a sunspot still emits a huge amount of light. Out of context, a sunspot would be brighter than an electric arc, and much brigter than a burning magnesium ribbon. Compared to the rest of the Sun, though, they appear dark.

With radii comparable to a small planet (the Sunspot pictured here appears to have roughly the same radius as planet Earth), sunspots are the Sun's natural chemistry labs. A whole host of molecules have been discovered in the spectra of sunspots,* including water. Water starts to form when temperatures get below roughly 4100°C. The trouble is that hot water is surprisingly difficult to get to grips with, as far as the theoretical chemistry of it goes. Its vibrations and rotations are so complex that it's been used in the past as a theoretical challenge for new calculation techniques to be tested on. Indeed, in its most congested regions, the spectrum of a sunspot contains about 50 spectral lines per wavenumber. If you're unfamiliar with molecular spectroscopy, suffice to say that that's a ludicrous amount!

In order to properly identify the water on the Sun's surface, new theory work was actually needed. The molecules in sunspots are so full of energy that they're halfway towards breaking themselves apart. So full of energy, in fact, that many of the molecules are present at energies that hadn't even been considered in laboratory studies (even if it were possible to attain such energies in the lab). It's surprising how little we actually know about hot water.

All of this can prove to be quite elsewhere in astronomy. Water is seemingly ubiquitous in the Universe. It's been found widely in interstellar clouds. Old oxygen-rich stars, particularly Mira variables, are full of it. In cool red dwarfs and brown dwarfs, water is expected to be the most abundant molecule after hydrogen. Water molecules have even been detected in over 100 other galaxies.

Importantly in the past couple of years, water molecules have been detected in the atmospheres of exoplanets. One of the most studied exoplanets is a hot jupiter known as HD 189733b, which has been found to have water vapour in its atmosphere. It was found using similar work to that used here, on sunspots. Life on this world seems unlikely. The place is far too hot. All the same though, the detection of water on planets in solar systems outside our own is spurred by the efforts of chemists like those looking at sunspots. Eventually, they give us hope that we might someday find a planet not unlike our own.



*Other molecules seen in sunspots include CO, OH, HCl, HF, CN and SiO. It's rather susprising at first, to realise how much chemistry can go on at the surface of a star.

Image source: APOD.
Image credit: Vacuum Tower Telescope, NSO, NOAO.

Wallace L, Bernath P, Livingston W, Hinkle K, Busler J, Guo B, & Zhang K (1995). Water on the sun. Science (New York, N.Y.), 268 (5214), 1155-8 PMID: 7761830


Polyansky O, Zobov N F, Viti S, Tennyson J, Bernath P F, & Wallace L (1997). Water on the Sun: Line Assignments Based on Variational Calculations Science, 277 (5324), 346-348 DOI: 10.1126/science.277.5324.346

"Science takes the romance out of things." This was an offhand comment made to me in conversation at the pub the other night. Is that really what people believe? Apparently, it is. It's regrettable, but I suppose the old stereotype of scientists being unable to appreciate the beauty in things is still going strong. While it's a sad fact that there are a number of scientists I've met who fit this image, it's certainly not true of all of us (indeed, the same is true of many non-scientists too). It may be the case that some scientists might scoff at the concept of beauty and dismissively explain away the natural phenomena which cause aesthetics. In my opinion, these scientists are doing it wrong.

To me, science unveils a myriad worlds of beauty which our fragile minds could scarcely have imagined if we hadn't taken the time to understand how it is that they exist. In turn, understanding how beauty can come about can only serve to heighten the fascination it holds, even for the beauty we're already quite familiar with.

Consider a sunset. There are few people alive who haven't taken at least a fleeting moment to appreciate the majesty of a sunset. The resplendent colours which fill the sky and the long shadows cast across the face of our planet. And if anyone reading this has never stopped to watch a sunset, I heartily recommend that you do. Take a second to appreciate how enthralling nature can be. You won't regret it.

But take a second also, to consider exactly what it is you're seeing. Three million times as massive as the Earth and almost 150 million kilometres away, the Sun is the source of all of these colours. Light from the Sun spans this huge distance at a dazzling speed, reaching planet Earth in just over 8 minutes. As that sunlight reaches our atmosphere it illuminates the billions and billions of molecules which make up the air. Even though air, to us, is completely transparent, the individual photons which make up that light can bounce haphazardly off these molecules, scattering in all directions. The light which is scattered most is blue light, which is what gives our sky the deep cerulean hue we admire so, on a warm summer afternoon. At sunset though, the sunlight reaching us has passed through so much of our atmosphere that there's very little blue left in it. This is why at sunset, the sky is reddest when it's low to the horizon, fading through orange and yellow higher in the sky.

Beauty is not a magic trick. Understanding how it works doesn't detract from its magnificence. If anything, the realisation of the sheer magnitude of what you're seeing should make it all the more captivating. Captivating, and ever so slightly humbling, with the realisation that each of us is just a tiny part of a huge planet, in a huger solar system. In an unimaginably vast Universe.

Just try and tell me that scientific understanding isn't beautiful.


"It does no harm to the romance of the sunset to know a little bit about it."
-- Carl Sagan

Image credit: Alvesgaspar, Wikimedia Commons

Remember IBEX? NASA's Interstellar Boundary Explorer has been mapping the outer limits of the solar system from a highly eccentric Earth orbit for almost a year now. It was designed to observe the Sun's heliosphere -- the bubble blown in the interstellar medium by the solar wind. What it found was such a surprise that it's left theoreticians and solar physicists a bit bewildered.



Seeing as interesting things happen when stellar material hits the interstellar medium, I'd been really looking forward to seeing what IBEX discovered, but this is a total curve ball. IBEX works by looking for energetic neutral atoms (or ENAs for short). These energetic atoms are created as the solar wind crashes into the interstellar medium. This scatters atoms in all directions, including a few which are scattered back at us. The actual number of atoms detected by IBEX is tiny, but it's detectors are sensitive enough to pick them up. Everyone was expecting there to be more of these atoms coming from one direction -- the previous idea was that as the Sun travels through the galaxy, most interstellar particles would strike one side. Its heliosphere would be drawn into a comet-like shape.

What IBEX saw was that wonky L-shaped thing in the image. It shows a region with a high concentration of charged particles, but what precisely causes this is a mystery. Abashedly, everyone's had to admit that they don't really know what's going on. This phenomenon certainly doesn't fit with any of the previous models or ideas about how the heliosphere works.

David McComas, principal investigator for IBEX suggests a fascinating explanation for this. This ribbon could actually be caused by interstellar magnetic fields! Looking at the image, this seems logical. The curved shape seen does look somewhat reminiscent of the ribbon-like aurora borealis seen on Earth. Reminiscent, but much much larger. I'm not an expert in this, but I suspect that magnetic fields at a galactic scale are poorly understood. More often than not, they simply seem to go unmentioned. On seeing such a dramatic example, I can't help but wonder what effects such a vast magnetic field might have on interstellar physics.

To read more, full results were published in Science this week.

A sunspot!!



Ok, ok, so it's not a very big or dramatic one, but it's a sunspot all the same (top left, in case you missed it). You might think this is rather a bizarre thing to be excited about, but I have my reasons. Allow me to elaborate...

The Sun, lately, has been quiet. Very quiet. As they would say in the movies, too quiet. It was reported last September that we've been in the middle of a lull in the solar wind. It's actually been the most quiescent period of solar inactivity for about 50 years, ever since we started observing it properly back in the 1960s.

The solar wind controls the size of the Sun's heliosphere -- the bubble of solar material that effectively protects us from interstellar space. When the solar wind is weak, it deflates the heliosphere, causing it to contract by millions of kilometres. The weaker wind may also allow many more energetic interstellar cosmic rays to penetrate our solar system.

Frankly, all of this isn't really as scary as it might sound at first. The solar wind is still more than potent enough to shield us from the perils of the interstellar medium, despite being weaker than normal. It's certainly been as weak in the past, without many ill effects to us down here on Earth... But observable sunspots mean that the Sun is waking up and beginning it's next solar cycle. This also means it should be a bit more interesting for those of us who like to keep an eye on the latest SOHO images. Frankly, that's pretty exciting. It almost feels like a New Year's celebration is in order...


Image taken from SpaceWeather.com

I'm sure a lot of my readers will know all about transits. A transit is any event when an object passes in front of (occults) a larger object. Things pass in front of stars all the time. We've watched Earth's sibling planets transit across the Sun's disk before, and NASA's Kepler mission watches for exoplanets transiting their parent stars...

But this is one of the few times anyone's captured people transiting the Sun! People in a space shuttle, to be precise. Right there in the centre of the picture above. Those aren't sunspots. That's Space Shuttle Atlantis preparing to grapple the Hubble Space Telescope. Kinda makes you feel small, doesn't it? In case you need further perspective, the uncropped image is available here from NASA's Flickr stream.

EDIT-- I was wrong. It wasn't the first time. That would've been a shot of Atlantis and the ISS in 2006 (rather photogenic, that Atlantis) -- by the very same photographer, no less! Unobservant me... A multitude of thanks to 6_bleen_7 for pointing that out!

Most of the astronomy blogosphere (and twittersphere for that matter) have been buzzing about the final service mission for Hubble this week. Understandably, as there are a couple of shiny new instruments being installed, like the Wide Field Camera 3, likely to give us Hubble's final set of stunning images. For the more scientifically minded, the repair of the Space Telescope Imaging Spectrograph (STIS) will hopefully allow for some exciting new scientific discoveries!

Actually, the internet's proven itself to be an excellent way of staying up to date on the news with current events like this one. Mission specialist, Mike Massimino has even been posting to twitter from orbit. Yes. From orbit. I don't know for certain, but I think that might be a historic first. Certainly, I've never heard of anyone posting to the internet from a space shuttle before. My inner geek finds that really rather exciting!

These stunning images were taken by French astrophotographer Thierry Legault and was no easy task, given that the Shuttle passed right the way across the Sun's disk in under a second! Thierry's images are excellent. If you have a moment, I'd advise you to go and look at some more!

Oooo... Maybe we really are a step closer to being able to predict space weather!

Interestingly, about the time I first started writing about near Earth supernovae, this fascinating paper was already published. Though by some quirk of fate, I've only just been able to get a copy of it to read!

So as I've said previously, there's some pretty compelling evidence that supernovae have gone off in our cosmic back yard in the past. We know, because they've left a few telltale signs. Isotopes with half lives shorter than the age of the solar system are a good clue. ⁶⁰Fe atoms have been found using this 'supernova archaeology' method, with over 100 times the expected natural abundance. To cut a long story short, the most likely reason for these isotopes are a supernova occuring near Earth around 2.8 million years ago (give or take 400,000 years) at an estimated 15-100 parsecs away. That's quite easily consistent with our old friend the Scorpius-Centaurus cloud (our local producer of such stellar popcorn).

But the big question being asked here is, how much would the Sun protect us from a nearby supernova? Thinking back again, the wind of particles given off by the Sun is pretty powerful. Powerful enough to blow a bubble in the interstellar medium (the heliosphere) and help shield us from interstellar gas and cosmic rays. So how would this interact with a nearby supernova? How much protection does the Sun give us?

Well Fields et al, based at the University of Illinois, have put together the first ever hydrodynamic simulation to study the interaction of the Sun's heliosphere with an expanding supernova remnant. Systemic, and in plenty of detail, they use observational data on the solar wind to create an idealised model (tailored to recreate the conditions around Earth's orbit), together with a Sedov-Taylor model of an expanding supernova remnant. Then they put the two models together and see what happens! As such, they can recreate a huge array of possible scenarios, varying solar wind speed, supernova distance, ISM density and other parameters.

The image to the right there is a snapshot of the Sun's heliosphere as it might look in the middle of a supernova shockwave. This is what could happen with an average solar wind speed, if a supernova occurred 10 parsecs away. The interesting thing is that the overall shape isn't too different to the heliosphere normally. Certainly, it's smaller, more compressed, longer and thinner... (actually, a lot smaller -- the termination shock is notmally around 75-90AU away, while here it's only 1.1AU!) Mind you, the side where the supernova blast is impacting still has a bow shock, the inside still has a termination shock encircling the Sun (the inner limit of where the supernova blast could reach). While there's a ragged looking trail of gas (caused by kelvin-helmholtz instabilities), Earth would be safe from the actual supernova blast wave itself. The black circle shows Earth's orbit, safely within the Sun's influence.

What's interesting is that the effect can be directly scaled. A stronger blast (say, from a closer supernova) or a weaker solar wind causes the heliosphere to shrink accordingly. If the solar wind were half its average (and incidentally, it's at a very low point at the moment), the termination shock would be just inside Earth's orbit. Scarily, this would mean the Earth might take the direct force of the supernova blast.

Still, it's heartening to know that a supernova 10 parsecs (that's around 33 light years) away probably wouldn't destroy the Earth! Ditto, it has some implications for astrobiology. Planets orbiting near to their stars would have a fair amount of protection, even from a supernova. This bodes rather well for the development of life on planets anywhere. A planet within a star's habitable zone would probably be fairly well protected by its parent star.

What this means is that it's highly unlikely that the supernova 2.8 million years ago actually hit us directly. The Sun would have given us plenty of shielding from the actual blast wave. More likely, all of that ⁶⁰Fe got to Earth as dust (supernova condensates... I've read about them somewhere before!), peppering the atmosphere like a shotgun blast. Even at the moment, much slower interstellar dust makes it as far into the heliosphere as Earth. We must've received a good dusting 2.8 million years ago!

The authors fully acknowledge that their model still needs work, reminding us that this is still a first ever model:

"Of course, the precise quantitative "cutoff" distance for terrestrial exposure will depend on the details of the problem, some of which we have simplified..."

Their plans are to build more detailed simulations to investigate the scenario even further, and their work shows a lot of promise. I'll bet they have some more interesting results already!

Brian D. Fields, Themis Athanassiadou and Scott R. Johnson (2008). Supernova Collisions with the Heliosphere The Astrophysical Journal, 678, 549-562 DOI: 10.1086/523622

Ever wonder what a star sounds like?
Stars certainly aren't silent. Actually, they constantly 'sing' by oscillating at certain frequencies. Using ESA's Corot satellite, astronomers have recorded these frequencies and made them into actual sounds. Click that link above to go to the BBC website and actually hear starsong!
(Much scintillation and sparklyness to Arianna for e-mailing that link!)

Obviously, actual sound doesn't travel through space. What you're hearing are the frequencies the star's vibrating at after they've been recorded by astronomers here on Earth. The tone is affected by a star's age and how many metals it contains. The fluctuations you hear come from the fact that the whole star is oscillating. Vibrating standing waves ripple through the star's body, and they can tell you a lot about the internal workings of the star itself.

In fact, they'd look something like this (for geeks and scientists, that's a l=5, m=4 p-mode vibration). This is just one of well over a million different ways a star can vibrate. It's overemphasised, of course, but the Sun is vibrating this way even as you read this.

The technique's called astroseismology. It all started around 1962, when a group studying the Sun noticed that the radiation emitted by the solar surface slowly changes with a period of about 5 minutes. Specifically, they were looking at lines in the Sun's spectrum, and noticing tiny doppler shifts over time. What they'd found were the acoustic harmonics in the Sun's surface.

Actually, this site has recordings of some more starsong.
As you'd expect, giant stars have a deep throbbing sound, while tiny, rapidly spinning white dwarfs are full of odd harmonics. You can even compare Alpha Centaurii A with Alpha Centauri B.

In a manner somewhat reminiscent of the molecular vibrations I study, stars have a number of different vibrational modes. The big difference is that while miniscule molecules have a handful of possible vibrations stars are enormous, so they have millions! The whole concept (with some more pretty visualisations of vibrating stars) is explained really rather well on this webpage, courtesy of St Mary's University's David Guenther.

The technique of actually listening to these vibrations, however, is a relatively new one; though it's fast becoming popular. More and more astronomers (such as Jodrell Bank's Tim O'Brien) are listening to sounds from space. It's easy to see why, with the eerie beauty of some of these sounds, though it's also a very useful scientific method!

No one seems to have been shouting too loudly about NASA's IBEX probe. In fairness I suppose, it isn't going to be looking at any planets or surveying any galaxies. From an astrochemical perspective though, IBEX is far more exciting than satellites like Fermi -- and that's saying something!

Because everyone likes acronyms these days, IBEX stands for Interstellar Boundary Explorer, and it's objective is to explore the very edge of the solar system, where interstellar space begins.

As any astrochemist will happily tell you, despite being technically a vacuum, interstellar space is far from empty. In fact, it's awash with all kinds of molecules, ions, dust grains and other lovely things that we astrochemists try very hard to identify.

So to explain exactly what IBEX will be looking at, here's a handy little picture...



The Sun, just like all other stars, has a stellar wind (or, when talking about the Sun, a Solar wind). It's constantly flinging streams of charged particles in all directions. The Solar wind is powerful enough that it actually blows a bubble in the interstellar medium, called a heliosphere. Some parts of the heliosphere are pictured above. For a start, it's big. Very big. Heading outwards, well past the Kuiper Belt, the first thing you reach is the Termination Shock. This is where the Solar wind begins to slow down significantly. It starts to compress and heat up. Incidentally, the Termination Shock varies. The more sunspots and flares the Sun is giving off, the stronger the Solar wind, so the further away the Termination Shock. Voyager II actually crossed the boundary 5 times!
(It recorded some data too...)

Cross the Termination Shock and you find yourself in the Heliosheath. This is where the Voyager probes now lie. Their current aim isto study the Heliosheath itself. It's a turbulent region, full of swirling gasses and plasmas, heated by the collision between the Solar wind and the Interstellar Medium (ISM). Though much is still unknown, it's thought that the heliosheath is drawn into a long teardrop shape, due to the Sun's orbit around the galaxy. The ISM pushes harder against one side, causing an elongated shape.

Finally, as the Solar wind becomes too weak to push back the ISM, you reach the Heliopause, the actual boundary of the solar system, and the edge of true interstellar space. As the Sun plows it's way around the galaxy though, it has one final effect. Stars create Bow Shocks as they plough their way through interstellar space, exactly the way a ship's bow cuts through water. It's not very obvious in The Sun's case, but it's been observed in several other stars. The effect's a lot more obvious if the star happens to be travelling through a nebula (like LL Orionis here)...



IBEX launches on October 19th. Let's hope it finds some interesting things!