OK I’m going to break my blogging silence and my aversion to blogging in my subject area to post about a really cool result that came out earlier this week.
Looking up at the night sky you see a hodge-podge collection of stars, perhaps a few thousand of the hundreds of billions of stars in the Galaxy. Some are extremely bright types of star that are really far away. Others like the Sun’s nearest neighbouring system Alpha Centauri are fairly run of the mill but appear bright because they are so close. But not all stars close to the Sun can be seen with the naked eye. Take Barnard’s Star, the second closest system to the Sun, it’s situated roughly twice as far away from us as Alpha Centauri but because it’s a red, faint type of star, it’s over 6,000 times fainter and 25 times too faint to see with the naked eye. This means that even though some stars are very close to us, they are so faint that we need to use a few tricks to pick them out from bright background stars.
One of the best tricks to use is to take a picture of the sky and look back a few years later and compare the positions of stars. Stars move around the Galaxy with different orbits and hence every star has a velocity with respect to the Sun. Due to their closeness, nearby stars appear to move more compared to background stars (their proper motion). This is simply a perspective effect, they aren’t actually moving through space faster. Hence if you look for stars moving quickly across the sky, chances are a lot of them will be near the Solar System. This isn’t simply a matter of cartography, if you want to pick out a population of faint objects, your best bet is to look close-by.
And that’s exactly what Kevin Luhman did. By taking the positions of objects observed by the WISE satellite, he found one which stuck out. It moved across the sky pretty fast and was very bright in infrared light. Looking back at images taken by other surveys he also found it detected there. This often happens in astronomy, sometimes you find an object nobody had noticed was interesting before but which may have been first detected 50 or even 100 years ago. Anyway, the object Luhman found was moving across the sky pretty fast. Well actually it wasn’t, nearby stars tend to have their motions measured in arcseconds per year. One arcsecond per year is the same angular speed as seeing the average tortoise walking at the distance of the Sun from Earth. The newly discovered high proper motion object was moving at about 2.8 Solar Tortoises, which is pretty big for stars. Well I say star, but it isn’t, it’s a brown dwarf, well actually not “a” brown dwarf.
Stars are fuelled by nuclear reactions in their core. These work because of the huge temperatures in their cores caused by all the mass above pushing down. It’s like the atomic nuclei in the core are caught at the bottom of a really big rugby ruck*. Anyway, they get so hot that they can sometimes overcome their mutual repulsion and fuse together. However some objects, with masses below about 8% of the Sun can’t reach the appropriate minimum temperature to begin stable fusion and hence are “failed” stars or brown dwarfs. When Luhman took a spectrum of his object, he found it was a brown dwarf, well actually while taking the observation he found that it was actually two brown dwarfs in orbit around one and other. Finally, using the data from the WISE satellite and other surveys he was able to work out its distance from an effect known as trigonometric parallax. This showed the two brown dwarfs are about 6.5 lightyears away, slightly more distant than Barnard’s Star.
My reaction to this was probably like others in my field, “how did we miss this?” Well the answer is simple, the system lies close to the Milky Way. The density of stars on the sky increases sharply as you go close to the plane of the Milky Way, meaning searches of nearby stars are often flooded with spurious candidates. Additionally the gas and dust in the plane make background stars appear redder and faint in the optical but still bright in the infrared. This can mimic the colour of brown dwarfs, again contaminating searches. Brown dwarf searches therefor often avoid the region around the Milky Way to make sure they can have clean samples without wading through a load of junk. Hence the extremely nearby, bright brown dwarf lay undiscovered for decades after it had first been detected.
And that brings me to my last point, this is a really cool discovery yet it hasn’t got the attention it deserves. The third closest system to the Sun was just found, that should at least be on the BBC News front page.
*There are no known instances of a rugby ruck leading to nuclear fusion
When I was younger one of my favourite game franchises was the Command & Conquer series, in particular Red Alert (1 and 2). They were real-time strategy, or RTS, games, where you built your base, harvested resources, trained your soldiers, and invested in high-tech weaponry all whilst being attacked by your opponents (either other players, or the computer AI). If I’m honest, my game tactics were always a little shaky. I was more likely to throw everything I had on mad, suicidal, missions against the other team, rather than spending the time to properly invest in the infrastructure of my base. In extreme cases I would even sell all my buildings, spend all the money on infantry and send everyone in. Surprisingly this actually worked. Sometimes.
My friend Tom however, he was good at these games. He always had a strategy. A proper one, not the crazy, oh-my-there’s-a-tesla-coil-right-there-RUN-AWAY!, one that I’d be using. He’s been spending time recently on StarCraft 2, another RTS game where you try to become master of a region of space by colonising planets, displacing the territory of the two other rival civilisations as you go.
Tom’s not just a game player though – he’s also an astronomer. Turns out when you combine gaming astronomers (Tom & his colleague Duncan) with real StarCraft gameplay data and realistic simulations of colonisation, based on our own Milky Way, what you end up with is a model of interstellar species expansion. Unsurprisingly the game is pretty evenly balanced (to prevent any one species or strategy from dominating), but the simulations do suggest that one of the races, the Terrans, tend to win out if they put pressure on their opponents early.
Using game data to investigate real-world problems has been around for a few years now. It began when researchers realised that the spread of a virtual plague in World of Warcraft shared many similarities with the spread of real viruses.
Tom and Duncan’s results aren’t meant to directly relate to how real aliens could be spreading through the Galaxy right now (and they definitely don’t want to give the impression that “…intellects vast and cool and unsympathetic, regarded this earth with envious eyes, and slowly and surely drew their plans against us”). However, they do demonstrate the potential power in-game data has for future work in this area.
Oh my. I’ve just looked at this, our much-neglected blog, and realised that the last post here was in November. The first thing I feel I should do today therefore is wish you all a very belated Happy New Year! Maybe I should go with a slightly early Happy Chinese New Year! instead.
It may sound like a weak excuse for the lack of activity around here, but we’ve all been really busy this past year. Three quarters of us have changed jobs and moved country, half of us have got married (though not to each other), and Niall’s taken the first steps on the road to pop stardom (though, and possibly in tribute to Beyonce, I’m pretty sure he’s miming):
This week is actually a very good time for me to write something here as last Wednesday was the 50th anniversary of astronomer Maarten Schmidt’s discovery that the apparently star-like object 3C273 was actually located far outside our own galaxy – several billion light years away in fact – and was, at the time, the most distant thing ever observed (thanks to Jen Gupta for the tip off). It came to be known as a quasi-stellar object or quasar, and we now know that it’s a galaxy with an active central massive black hole, which is sucking material down onto it at a voracious rate. It’s star-like appearance is because the light coming from this nucleus outshines the combined light from all the stars within it (as I’ve written about here before). Here’s Maarten Schmidt explaining the significance of this discovery in an interview from 1975:
…I would say that indeed it was, in a sense, the birth of the present era of exotic phenomena, exotic and explosive phenomena in astronomy, with the quasars, the pulsars, the x-ray binaries, the black hole, the 3 deg. background radiation. I mean all these things were yet to come. The quasars suddenly started it and since then just about every two years there has been a major development of another discovery. Astronomy in an accelerated development that is just unbelievable. I mean before 1963 things were so unlike after 1963, there was no way to compare it. So in a sense the agony and the pressure of making a good on-the-spot scientific judgment just in one day essentially, the fifth of February, was a very interesting one. Because we had not been subjected to this yet. Later on it was much easier for people to accept extraordinary things in astronomy because we’ve seen it as I said every two years we’ve seen them. This has come on with about five to six, even with seven different types of phenomena including the gamma ray bursts that you may have heard about. Fantastic things. You never heard things like it in astronomy! And if they came, it was one a lifetime… So it was the beginning of an era that, of course we didn’t know at that time, we couldn’t help but realize that the quasars would play a very important role from then on, it was clear enough.
SCHMIDT, M. (1963). 3C 273 : A Star-Like Object with Large Red-Shift Nature, 197 (4872), 1040-1040 DOI: 10.1038/1971040a0
Two interesting videos were posted yesterday on the problems with the current state of high school physics education. The first is an open letter to Barack Obama from Minute Physics, pleading for the US physics curriculum to include results more recent than the Civil War:
In the second Nottingham academics, and regular contributors to the Sixty Symbols video series, give their views on the situation in the UK:
Personally I found the concepts taught in my school physics courses much easier to grasp once my teachers explained them using the proper maths (mainly calculus!)
So you’ve probably heard the exciting news, that a small, earth-mass planet has been identified around one of the components of Alpha Centauri. It’s the nearest neighbouring system to our Sun. Despite that it isn’t the brightest star in the sky (that’s Sirius), also it’s a southern star so is not very familiar to those of us who live in the Northern hemisphere. In-fact I didn’t see it until I was 28 and had moved to Hawai`i. Here’s a picture I took of it rising above Kilauea.
Because it was so far south, Alpha Cent. wasn’t well studied by early European astronomers. In the 1830s Thomas Henderson, the first Astronomer Royal for Scotland measured its distance using trigonometric parallax. This was the first distance measurement to a star other than the Sun. However he hesitated in publishing the result and Bessell scooped him to the first published distance to a star (61 Cygni).
The system itself actually consists of three stars. The two brightest components appear as a single source to the naked eye. The two stars orbit each other at a distance about 17-18 times the Earth-Sun distance. There’s third star in the system, Proxima Centauri. It’s 100 times too faint to see with the naked eye and while the two brighter components are of similar mass to the Sun, Proxima is less than an eighth of that. That said for people like me who study low mass stars, it’s still not that low mass. It was discovered by another Scot, Robert Innes who worked as a wine merchant in Australia before taking up astronomy fulltime. Simply, he found a star with a similar motion across the sky to Alpha Centauri and given their close positions (yet it’s still 17,000 times the Earth-Sun distance from Alpha Centauri AB), deduced they were a pair. This is what I do a lot in my research, but I use large catalogues produced by data pipelines, he used many painstaking measurements by hand. Sometimes I feel like modern astronomy is cheating. One interesting side-note, this double star with a wide companion set-up seems to be more common than a single star with a wide low mass companion. A rather nice recent paper by Peter Allen and others quantified this and indicated that this may say something about how these systems form.
A quick note about the planet. It appears to be too close to the star to sustain liquid water and hence life. This system has a fairly complicated Habitable Zone. The planet is orbiting the smaller of the two stars but it will also be heated by Alpha Centauri A. Duncan Forgan wrote a paper about this earlier this year saying the difference will be small but will induce oscillations of a few degrees. Also sometimes on the surface of the planet Alpha Centauri B will have set but the planet will still be lit by Alpha Centauri A. This will of course change as the two stars orbit each other. Duncan has a nice blog post about the paper where he also talks about sleeping rhythms on a hypothetical planet around Alpha Cent B. When Alpha Centauri A is on the other side of Alpha Centauri A from the planet I guess sunset will look a bit like that on Tatooine. Although with a different brightness ratio between the two stars.
So it’s Alpha Centauri has a planet. It isn’t able to support life, but maybe there’s another one in the system that can. What this discovery makes me think of is Civilisation. No, not the noted BBC TV series, but the classic Sid Meier strategy game. One of the victory conditions was to send a spacecraft to Alpha Centauri. I never got that far, on more difficult levels my civilisation would die in the Bronze Age and in the harder levels I’d get bored of nuking phalanxes in about 1900 and give up. However if I hadn’t given up perhaps I could have built a ship to head for what the Nature press release calls a “scorched barren rock”.
A week ago I posted about some of the videos that had been made at .astronomy4. The video I was involved in (Sh*t Astronomers Say) has so far got over 5,000 hits. I find that a little scary and it’s been odd having colleagues asking me questions on desk head-butting techinques. While this wasn’t a video with an agenda, I think there is a lesson to be learned from the post. In other words, I think we learned something today……
You remember the end of He-Man where in an earnest tone Ram-Man would explain that it’s bad to ram things with your head or Beast-Man would tell you not to put lit fireworks in your mouth*. Anyway, this is a bit like that. During the drafting of Sh*t Astronomers Say, we basically made a big list of things that we heard a lot. In many cases we added things because they are frequently done and they are annoying. Some things are annoying and are trivial, others get in the way of astronomers doing and communicating science.
The main bugbear for me was a lot of the stuff that went in to the talk section. I hate going to talks, sitting somewhere in the middle to back of the room and then not being able to see anything. The number one problem is with plots. About the worst thing you can do with a plot is jsut take the version from the paper and then slap it up there. Normally the axes will be unreadable for half the audience and often the datapoints will be a confusing jumble. Then there’s the issue of colour schemes, many are headache-inducing but often they just confuse the audience. Remember that about 8% of men and 0.4% of women are colourblind so avoid reds and greens that may be indistinguishable (I’m biased here as I’m red-green colourblind). Finally the last point, the organisors have been very nice to give you a slot to talk in, don’t outstay your welcome. There’s nothing worse than someone bringing 30 slides to a 10 minute talk and proceeding to go over each one in great detail. OK maybe regicide is worse but it’s borderline.
Was there a particular bugbear of your’s in the video? Feel free to comment on it below.
One thing before I outstay my welcome, we are going to have a go at a crowdsourced follow-up. Below are the details,
Did we leave out your personal favorite saying? Want to contribute to a new, crowdsourced version of Sh*t Astronomers Say? Send submissions to email@example.com by August 31! We’ll accept any video+audio formats compatible with iMovie – you can even record with PhotoBooth! (You have a Mac, right?!?!) Please keep videos under 30 seconds and leave enough space between sayings for editing. Include your name, institution, occupation (undergrad/grad/postdoc/faculty/etc) and filming location so we can give you proper credit and estimate the diversity of contributions. We can’t guarantee we’ll be able to use every submission, but we’ll do our best!
*OK I made up the last one, but the Ram-Man one is real
Last week I (along with 49 others) attended the 4th installment of the .astronomy conference. Part of the conference was a Hack Day where people went off and designed useful bits and bobs for astronomy. One example was the Zoonibot which is designed to monitor the Planet Hunters forum to help users with classifications have posted.
For the hack I was involved with we did a video. What better way to promote the science of astronomy than with in-jokes.
Also doing a video production were Amada and Nicole who made a response to the silly, shallow and demeaning “Science it’s a a Girl Thing” video. As you can see there’s is a lot slicker than ours which indicates they actually know how to use iMovie properly.
And yes, I know the sound is only on one side.
I wrote the following post yesterday, but I fell asleep before I could do anything with it. It’s about the first set of results from the Baryon Oscillation Spectroscopic Survey (BOSS), part of Sloan Digital Sky Survey-III project, which we announced to the science community and to the press yesterday. How this whole project was picked up by the press in a way I hadn’t anticipated is the matter for another post. What really matters is the science, and the science – if you don’t mind my exceedingly biased opinion – is just excellent.
I’m now making my way back home from this year’s National Astronomy Meeting (NAM) 2012 in Manchester. I love NAM. It’s always a chance to see old friends and listen to good science, to catch up on gossip and long-promised pints. This year, I did almost none of these things. The reason is that one of the teams I’m working with announced a pretty exciting set of science results today, in the form of six papers. This involved submitting the papers to the journals and to the arXiV yesterday. And that means that yesterday we panicked about coordinating submission of 6 papers across the globe, and today we panicked about press conferences, press interviews and science talks.
So what was all the fuss about? In essence, it all comes down to a map. You see, 14 years ago a number of astronomers announced a pretty remarkable observation: that the Universe’s expansion is accelerating. If the Universe is made only of matter (dark or bright), and the only force acting on large scales is gravity, then the Universe’s expansion should be doing exactly the opposite. This discovery, based on the observation of distant supernovae type Ia explosions (awarded with the Nobel Prize for Physics last year, and that I’ve covered here before), shook our cosmological model to the ground; the job of the science community was to build it back up.
There are a number of proposed explanations for this phenomenon, which astronomers named Dark Energy. The simplest from a theoretical point of view (but not from a conceptual point of view – more on that later) is the idea of a Cosmological Constant – a simple constant term in Einstein’s equations of General Relativity that would naturally explain the acceleration. In physical terms, this would equate to a rather bizarre property of empty space, a sort of vacuum energy that would cause space itself to expand. Einstein originally included this constant in his equations to ensure that the Universe was static. When Hubble announced his observation that the Universe was expanding, Einstein removed this constant from his theory and allegedly referred to it later as is ‘biggest blunder’. It’s ironic that we now put it back in – albeit with the opposite sign – to explain an observation that probably never crossed Einstein’s mind.
At the other extreme of possible explanations for Dark Energy we have modified gravity models. Einstein’s theory of General Relativity has passed some stringent tests at solar-system scales. But if this theory breaks down on very large scales, or at very low densities, then perhaps this acceleration is just really an illusion that stems from a ill-conceived theory.
So which is it? How can we tell? That’s where this map comes along. It turns out that one of the most effective ways to learn more about Dark Energy is to map out how matter is distributed in the Universe. As most of the matter out there is in the form of Dark Matter, and because Dark Matter doesn’t lend itself to an easy detection, we map galaxies instead. Galaxies are faithful (if sometimes cheeky) tracers of Dark Matter, so by mapping their positions we are essentially mapping the matter in the Universe. We map their position in the sky, and we use spectrographs to measure a redshift to each individual galaxy – resulting in a three-dimensional map of our Universe.
This map gives us two main ways with which to study Dark Energy.
Firstly it gives us the means with which to measure the expansion rate of the Universe. If we want to learn about this new phenomenon, then we best start by carefully measuring its effects. We do this by finding a measuring rod in the Universe, something whose size is known. Thankfully, Nature was kind enough to provide us with such a measuring rod, and this is how it happened: shortly after the Big Bang, the Universe was so hot and dense that all matter was in the form of a plasma and the Universe behaved very much like a fluid. This fluid wasn’t all of uniform density – some parts were denser than others, and these small gradients set up pressure waves in the fluid that propagated at a speed related to the density of the fluid (that in turn depends on its composition, temperature, etc). They set up ripples if you like, of a characteristic wavelength, that can still be detected in the distribution of galaxies today.
These are called Baryon Acoustic Oscillations. ‘Baryon’ because they exist only due to the interaction of baryonic (normal, i.e., not dark) matter with radiation at extreme temperature and densities; Acoustic because they are pressure driven, just like sound is; and Oscillations because they are waves. BAO, for short.
We know this wavelength – or size – pretty well by looking for example at the cosmic microwave background. So if we can measure it at different times of the Universe’s history, we can map out its expansion in a very clean and robust way. And we can measure it, by looking at the distribution of galaxies at times in the past (or equivalently, at galaxies at different distances from us – thanks to the finite speed of light). This BAO size shows itself in the distribution of galaxies as a distance at which galaxies are preferentially distanced from one another. The magic number is around 500 million light-years. Let me quote Daniel Eisenstein on this, the director of SDSS-III,
“Because of the regularity of those ancient waves, there’s a slightly increased probability that any two galaxies today will be separated by about 500 million light-years, rather than 400 million or 600 million.”
And that is the whole point – to measure the distance at which we find a slight excess of finding pairs of galaxies. As it has been expanding with the size of the Universe, tracking it means tracking the cosmic expansion.
BOSS mapped the positions of 250,000 galaxies that are roughly 6 billion light years away for Earth. We measured the BAO scale with a phenomenal 1.7% precision. When we combined it with other BAO scale measurements, we found an expansion rate consistent with a Universe dominated by Dark Energy in the form of a cosmological constant, and otherwise consistent with the General Relativity.
But this isn’t the whole story. The trouble is that you can always modify the laws of gravity to match any expansion history measurement in such a way that it becomes almost impossible to tell the difference between a GR + Dark Energy combo, from a Modified Gravity (MG) and no Dark Energy model if we just measure the Universe’s expansion. There’s one more test we can do, however, that tests gravity directly.
The galaxy map we measured was shaped by the continual tug of war between the two dominant forces in the Universe – on one hand we have Dark Energy accelerating things apart, and on the other we have gravity, pulling everything together.
Gravity causes structure to form – small fluctuations in matter density in the early Universe gave rise to the largest structures in the Universe today (I’m talking about galaxies, and clusters of galaxies) simply due to gravity. Importantly for the question at hand, this growth allows us to test our understanding of the laws of gravity. If gravity behaves as Einstein suggested it did, even at these colossal scales, we know how fast structure should be growing in the Universe.
Gravity and dark energy affect the motions of galaxies in different ways. By large, the motion of a galaxy is set by the expansion of the Universe (hence the relevance of the BAO measurements). But if you look closely enough, if you have enough galaxies, you can also detect the velocity component due to growth; due to gravity.
Now, remember that our map is really a redshift map. On one direction and one direction alone – that is along our line of sight – it gives us a recession velocity, or redshift. As galaxies are infallling into clusters, as structure grows, galaxies appear to be closer than they really are along this direction. This distorts our map in a very peculiar way, squashing it along our line of sight. A faster growth of structure results in a more prominent ‘squashing’ signal. This gives the name to this technique – redshift space distortions.
My measuring these distortions we can measure the rate at which structure grows and we can test gravity. BOSS, with its large volume and number of galaxies, set a rigorous test of Einstein’s theory of gravity at these very large scales. And what is outstanding is that it still seems to work.
This is a profound statement about the physical nature of our Universe, and one that we don’t make lightly. Of course we need to continue to look ahead. As we gather more data (and BOSS is only one third of the way through collecting data), we can make more precise measurements and more interesting tests.
To quote the principal investigator for BOSS, David Schlegel: “If there are surprises lurking out there, we expect to find them.”
Lauren Anderson, Eric Aubourg, Stephen Bailey, Dmitry Bizyaev, Michael Blanton, Adam S. Bolton, J. Brinkmann, Joel R. Brownstein, Angela Burden, Antonio J. Cuesta, Luiz N. A. da Costa, Kyle S. Dawson, Roland de Putter, Daniel J. Eisenstein, James E. Gunn, Hong Guo, Jean-Christophe Hamilton, Paul Harding, Shirley Ho, Klaus Honscheid, Eyal Kazin, D. Kirkby, Jean-Paul Kneib, Antione Labatie, Craig Loomis, Robert H. Lupton, Elena Malanushenko, Viktor Malanushenko, Rachel Mandelbaum, Marc Manera, Claudia Maraston, Cameron K. McBride, Kushal T. Mehta, Olga Mena, Francesco Montesano, Demetri Muna, Robert C. Nichol, Sebastian E. Nuza, Matthew D. Olmstead, Daniel Oravetz, Nikhil Padmanabhan, Nathalie Palanque-Delabrouille, Kaike Pan, John Parejko, Isabelle Paris, Will J. Percival, Patrick Petitjean, Francisco Prada, Beth Reid, Natalie A. Roe, Ashley J. Ross, Nicholas P. Ross, Lado Samushia, Ariel G. Sanchez, David J. Schlegel Donald P. Schneider, Claudia G. Scoccola, Hee-Jong Seo, Erin S. Sheldon, Audrey Simmons, Ramin A. Skibba, Michael A. Strauss, Molly E. C. Swanson, Daniel Thomas, Jeremy L. Tinker, Rita Tojeiro, Mariana Vargas Magana, Licia Verde, Christian Wagner, David A. Wake, Benjamin A. Weaver, David H. Weinberg, Martin White, Xiaoying Xu, Christophe Yeche, Idit Zehavi, & Gong-Bo Zhao (2012). The clustering of galaxies in the SDSS-III Baryon Oscillation
Spectroscopic Survey: Baryon Acoustic Oscillations in the Data Release 9
Spectroscopic Galaxy Sample arXiv arXiv: 1203.6594v1
Ashley J. Ross, Will J. Percival, Ariel G. Sanchez, Lado Samushia, Shirley Ho, Eyal Kazin, Marc Manera, Beth Reid, Martin White, Rita Tojeiro, Cameron K. McBride, Xiaoying Xu, David A. Wake, Michael A. Strauss, Francesco Montesano, Molly E. C. Swanson, Stephen Bailey, Adam S. Bolton, Antonio Montero Dorta, Daniel J. Eisenstein, Hong Guo, Jean-Christophe Hamilton, Robert C. Nichol, Nikhil Padmanabhan, Francisco Prada, David J. Schlegel, Mariana Vargas Magana, Idit Zehavi, Michael Blanton, Dmitry Bizyaev, Howard Brewington, Antonio J. Cuesta, Elena Malanushenko, Viktor Malanushenko, Daniel Oravetz, John Parejko, Kaike Pan, Donald P. Schneider Alaina Shelden, Audrey Simmons, Stephanie Snedden, & Gong-bo Zhao (2012). The clustering of galaxies in the SDSS-III Baryon Oscillation
Spectroscopic Survey: Analysis of potential systematics arXiv arXiv: 1203.6499v1
Rita Tojeiro, W. J. Percival, J. Brinkmann, J. R. Brownstein, D. Eisenstein, M. Manera, C. Maraston, C. K. McBride, D. Duna, B. Reid, A. J. Ross, N. P. Ross, L. Samushia, N. Padmanabhan, D. P. Schneider, R. Skibba, A. G. Sanchez, M. E. C. Swanson, D. Thomas, J. L. Tinker, L. Verde, D. A. Wake, B. A. Weaver, & G. Zhao (2012). The clustering of galaxies in the SDSS-III Baryon Oscillation
Spectroscopic Survey: measuring structure growth using passive galaxies arXiv arXiv: 1203.6565v1
Marc Manera, Roman Scoccimarro, Will J. Percival, Lado Samushia, Cameron K. McBride, Ashley Ross, Ravi Sheth, Martin White, Beth Reid, Ariel Sánchez, Roland de Putter, Xiaoying Xu, Lauren Anderson, Andreas A. Berlind, Jonathan Brinkmann, Bob Nichol, Francesco Montesano, Nikhil Padmanabhan, Ramin A. Skibba1, Rita Tojeiro, & Benjamin A. Weaver (2012). The clustering of galaxies in the SDSS-III Baryon Oscillation
Spectroscopic Survey: a large sample of mock galaxy catalogues arXiv arXiv: 1203.6609v1
Ariel G. Sanchez, C. G. Scoccola, A. J. Ross, W. Percival, M. Manera, F. Montesano, X. Mazzalay, A. J. Cuesta, D. J. Eisenstein, E. Kazin, C. K. McBride, K. Mehta, A. D. Montero-Dorta, N. Padmanabhan, F. Prada, J. A. Rubino-Martin, R. Tojeiro, X. Xu, M. Vargas Magana, E. Aubourg, N. A. Bahcall, S. Bailey, D. Bizyaev, A. S. Bolton, H. Brewington, J. Brinkmann, J. R. Brownstein, J. Richard Gott III, J. C. Hamilton, S. Ho, K. Honscheid, A. Labatie, E. Malanushenko, V. Malanushenko, C. Maraston, D. Muna, R. C. Nichol, D. Oravetz, K. Pan, N. P. Ross, N. A. Roe, B. A. Reid, D. J. Schlegel, A. Shelden, D. P. Schneider, A. Simmons, R. Skibba, S. Snedden, D. Thomas, J. Tinker, D. A. Wake, B. A. Weaver, David H. Weinberg, Martin White, I. Zehavi, & G. Zhao (2012). The clustering of galaxies in the SDSS-III Baryon Oscillation
Spectroscopic Survey: cosmological implications of the large-scale two-point
correlation function arXiv arXiv: 1203.6616v1
Beth A. Reid, Lado Samushia, Martin White, Will J. Percival, Marc Manera, Nikhil Padmanabhan, Ashley J. Ross, Ariel G. Sánchez, Stephen Bailey, Dmitry Bizyaev, Adam S. Bolton, Howard Brewington, J. Brinkmann, Joel R. Brownstein, Antonio J. Cuesta, Daniel J. Eisenstein, James E. Gunn, Klaus Honscheid, Elena Malanushenko, Viktor Malanushenko, Claudia Maraston, Cameron K. McBride, Demitri Muna, Robert C. Nichol, Daniel Oravetz, Kaike Pan, Roland de Putter, N. A. Roe, Nicholas P. Ross, David J. Schlegel, Donald P. Schneider, Hee-Jong Seo, Alaina Shelden, Erin S. Sheldon, Audrey Simmons, Ramin A. Skibba, Stephanie Snedden, Molly E. C. Swanson, Daniel Thomas, Jeremy Tinker, Rita Tojeiro, Licia Verde, David A. Wake, Benjamin A. Weaver, David H. Weinberg, Idit Zehavi, & Gong-Bo Zhao (2012). The clustering of galaxies in the SDSS-III Baryon Oscillation
Spectroscopic Survey: measurements of the growth of structure and expansion
rate at z=0.57 from anisotropic clustering arXiv arXiv: 1203.6641v1
So I ave a confession to make, this time last week I’d never seen the Northern Lights. Growing up near Edinburgh it’s a bit too far south and often cloudy when there are solar storms. Nijmegen and Heidelberg are a bit too far south and as for Hawai`i forget it. So a week ago, along with a few other astronomers (and an accountant) from Heidelberg, I set off for the Arctic Circle. This sounds a lot more intrepid than it actually was, booking a flight to Tromsø and hiring a car.
Anyway, enough about my jaunt, here’s some nice aurora pictures. I don’t have a fancy DSLR so I was using my Sony DSC-H2 which is apparently a “bridge camera”. Additionally the tripod is only a small pocket one so there is a small amount of camera-shake on some of the star images.
And here’s a time-lapse of the aurora changing over about 5 minutes. Note the Pleiades star cluster setting in the background.