Make yourself feel good

December 10, 2008

I am at least fourth off the blocks here … but I recommend you go visit http://www.physics.ox.ac.uk/skyphoto , get a piece of history, help a very sick child, and give yourself a nice warm christmassy glow. The basic idea is selling framed prints from old Palomar Sky Survey plates, to raise money for Alexander Thatte, the son of two Oxford astronomers, who is battling leukaemia, and whose last chance may be a new anti-body treatment. I haven’t met Alexander, but his parents are lovely people and they all deserve a break.  Apparently there are even copies signed by Jocelyn Bell Burnell … oooohhh

Old plates really are beautiful …  like a few other locals, I rescued a few glass positives from the non-survey part of the UK Schmidt collection, and a lot more went to the local art school .. but framed prints for charity is a great idea.

Visit the web site and do something.


UKIDSS world release

January 10, 2008

UKIDSS logo

As I warned just before Xmas in this post, the first world release of UKIDSS has now gone public, with a press release at the AAS. The blogosphere is picking it up, here, here and here. You have no idea how nice it feels after a couple of weeks of STFC-cuts politics.. This has been my baby since 1998 … but others have done much more work than me. Thanks especially Steve Warren, Nige Hambly, and Mike Irwin. Steve doesn’t seem to have a home page. This isn’t him.

Key links : explanations at the UKIDSS web site; data access at the WFCAM Science Archive; and Mike Read’s groovy pannable Milky Way.


Explore the infrared sky

December 21, 2007

UKIDSS logo

Most of this week I was actually doing some science for a change, at a workshop in ESO with all my UKIDSS chums. We just issued our third data release, which with exquisite taste we have called DR3. UKIDSS is now the biggest Infrared Sky Survey ever made, in terms of database size, number of objects, and effective volume (but not sky area). DR3 is announced on the UKIDSS web site, and you can get the data at the WFCAM Science Archive (WSA). Or at least you can if you are European.. but also DR1 is about to go world public, so all the Americans can get at it. This will be announced at the upcoming AAS meeting.

Mostly the WSA is for serious pro work, not for public consumption of pretty pix. However, our secret weapon Mike Read has knocked up a lovely pannable zoomable mosaic of the Galactic Plane Survey. Its still kinda patchy, but full of gorgeous things. Try it out.


Cows, Quasars, and Cosmic Rays

August 23, 2007

Day-4 at the Joint European National Astronomy Meeting. Much stuff today about Very High Energy Astronomy. This was hot stuff some decades ago, but is now undergoing a revival. Felix Ahoronian showed how TeV astronomy is finally taking off, with HESS, MAGIC, and VERITAS detecting real sources at high S/N. John Carr reviewed neutrino astronomy – under the sea (ANTARES), under lakes (BAIKAL), and under the Antarctic Ice (AMANDA) – which seems just on the brink of becoming real astronomy (roll on ICECUBE). These are maybe the last new windows on the Universe. Meanwhile Vahe Petrosian reviewed particle acceleration in the Universe, and argued that shock acceleration is not the solution to everything as most people have assumed for thre decades ; the answer is stochastic (second order Fermi) acceleration, and the snag is we need to understand turbulence …

Last night we had our excursion to Byurakan Observatory. As ICows and 2.6m at Byurukan explained a few days ago, this is something of a pilgrimage for Active Galaxy and Quasar fans, especially because this is where Markarian and Arakelian undertook their historic objective prism surveys, searching the cosmos for the blue and emission line objects – especially starburst galaxies and active galactic nuclei.

Its a beautiful observatory, spread out over a rural setting on the slopes of Mount Aragatz, and with a stunning view of the enormous Mount Ararat (of Noah’s Ark fame..). There are cows all the over the place (see pic-1). This is is nearly as good as the AAO being overrun with kangaroos. In the dalek-like 2.6M dome, there isYours truly on the BAO 2.6m controls a control system that seems to come from the Ark. As well as analogue dials, there are two computers, but they are Pentium IIIs… Pic-2, taken by Jonathan Tedds, shows yours truly pretending to control the telescope but actually coming out a bit Phantom of the Opera-ish.

Following this there was a lovely outdoor dinner on the longest table I have EVER seen. I tried hard to be rude to various French astronomers but they are just too ready with the timed riposte and le bon mot. Dammn.

Yes Yes I know Google Sky got released today but the network here is so crap I can’t really try it out yet.


Exploring the Cosmos Part III : The End of Astronomy ?

May 10, 2007

OK folks, here is Andy’s entry for the possibly overcrowded “end of science” market. I am not really making a case that Astronomy as a whole is finished – just that the Golden Age of Surveys is closing. This is not for any profound reason, but just because we have already ticked off the easy wins, and there is only so much money in the world.

This material is recycled from my long overdue article for “Astronomy and Geophysics” – its the written version of a review talk at last year’s National Astronomy 2006 meeting. (Sorry Sue). The astro-ph version is here. Off we go:

In 1950, the universe seemed to consist of stars, and a sprinkling of dust. Over the last fifty years, the actual diverse and bizarre contents of the universe have been successively revealed as we surveyed the sky at a series of new wavelengths. Radio astronomy has shown us radio galaxies and pulsars; microwave observations have given us molecular clouds and the Big Bang fossil background; IR astronomy has shown us ultraluminous starburst galaxies and brown dwarfs; X-ray astronomy has given us collapsed object binaries and the intra-cluster medium; and submm astronomy has shown us debris disks and the epoch of galaxy formation. As well as revealing strange new objects, these surveys revealed new states of matter (relativistic plasma, degenerate matter, black holes) and new physical processes (bipolar ejection, matter-antimatter annihilation). Having opened up gamma-rays and the submm with GRO and SCUBA, there are no new wavelength windows left. Has this amazing journey of discovery now finished ?

Well… wavelength is not the only possible axis of survey discovery space. Lets try some others.

Photon Flux. We could just go deeper. Historically, this has been as productive as opening new wavelength windows. The classic example is the discovery of the entire extragalactic universe, which did not become apparent until reaching ten thousand times fainter than naked eye observations, requiring both large telescopes and the ability to integrate. We can now see things ten billion times fainter than the naked eye stars. However, we have reached the era of diminishing returns. The flux reached by a telescope is inversely proportional to diameter D but its cost is proportional to D**3. Significant improvements can now only be achieved with world-scale facilities, and orders of magnitude improvements are unthinkable. The easy wins have been covered already – our detectors now achieve close to 100% quantum efficiency; we have gone into space and reduced sky background to a minimum; and multi-night integrations have been used many times. We will keep building bigger telescopes, but it no longer seems the fast track to discovery.

Spectral resolution. Detailed spectroscopy of individual objects is of course the key technique of modern astrophysics, but what about spectroscopic surveys ? This has been a big winner over the last few decades, because the spectrum of a galaxy gives you the redshift, and so the distance. This way we mapped out the Universe in 3D. We were not expecting the voids, bubbles and walls that were found in the galaxy distribution in the 1980s. This industry will continue, but there is no obvious new barrier to break. Narrow band imaging surveys centred on specific atomic or molecular features (21cm HI, CO, H-alpha) have been fruitful, but again its not obvious there is anywhere new to go. Some of my X-ray chums have suggested that deep X-ray surveys are the next-big-thing. I can see they will be v.good, but I can’t see it really cracks open a new part of parameter space.

Polarization. Polarisation measurements of individual objects are a very important physical diagnostic, but are polarisation surveys plausible ? Surveys of samples of known objects to the 0.1% level have been done, with interesting results but no big surprises. Perhaps blank field imaging surveys in four Stokes parameters would turn up unexpected highly polarised objects ? This has essentially been done in radio astronomy but not at other wavelengths.

Spatial resolution. If we can just resolve tiny tiny detail, perhaps we will see something really new ? This is the dominant big-project target of the next few decades, and of course is the real point of Extremely Large Telescopes. Put together with multi-conjugate Adaptive Optics, we hope to achieve both depth and milli-arcsec resolution at the same time. However, the royal road to high spatial resolution is through interferometry. Surveys with radio interferometers in the twentieth century showed the existence of masers in space, and bulk relativistic outflow. In the twenty first century we will be doing microwave interferometry on the ground (ALMA) and IR interferometry in space (DARWIN/TPF), hoping to directly detect Earth-like planets around nearby stars. So there is excitement for at least some time to come; however, as with photon flux, we are hitting an economic brick wall. Significantly bigger and better experiments will be a very long time coming.

Time. The observation of temporal changes has repeatedly brought about revolutionary changes in astronomy. Classic example number one is Tycho’s supernova, which cracked open the crystal spheres. Classic example number two is the measurement of stellar parallax, which showed how unspeakably vast the Universe is. The last two decades has seen a renaissance in this area, with an impressive number of important discoveries from relatively cheap monitoring experiments – the discovery of extrasolar planets from velocity wobbles and transits; the discovery of the accelerating universe and dark energy from supernova campaigns; the location of substellar objects from survey proper motions; the existence of Trans-Neptunian Objects, and Near Earth Objects (killer rocks in space !); the final pinning down of gamma-ray burst counterparts; and the limits on dark matter candidates from micro-lensing events. The next decade or two will see more ambitious photometric monitoring experiments, such as PanSTARRS and LSST, and a series of astrometric missions, culminating in GAIA, which will see external galaxies rotating. Overall, the “time window” is well and truly opened up. However, the temporal frequency axis is far from fully explored. My instinct is that this technique will continue to produce surprises for some time.

Non-light channels : particles. The origin of Cosmic Rays was one of the key puzzles of the twentieth century, and still can’t be considered solved. But you can’t really do surveys – indeed the central mystery has alway been where cosmic rays come from. Today, the underground experiments trying to directly detect Dark Matter particles are confronting what is arguably the most important problem in physics, let alone astrophysics. But again no survey is plausible. The big hope is neutrino astrophysics. Neutrinos should emerge from deep in the most fascinating places that we could otherwise never see – supernova cores, the centres of stars, the interior of quasar accretion discs. Measurement of solar neutrinos has solved a long standing problem, and set a challenge for particle physics – but what about the rest of the Universe ? New experiments such as ANTARES (under the sea) and AMANDA (under the ice) seem to be clearly detecting cosmic neutrinos, but no distinct sources have yet emerged. Possibly the next generation (ICECUBE and KM3NET) will get there. This looks like the best bet for genuinely unexpected discoveries in the twenty first century.

Non-light channels : gravitational waves. Like neutrinos, we know that gravitational waves have to be there somewhere, and their existence has been indirectly proved by the famous binary pulsar timing experiment. However after many years of exquisite technical development, we still have no direct detection of a gravitational wave. The space interferometer mission LISA should finally detect gravitational waves, unless current predictions are badly wrong. However even LISA will not produce a genuine survey. We will detect many events and understand more astrophysics, but will have essentially no idea where they came from, except that hopefully some will correlate with Gamma-ray bursts. If we see totally unexpected signals, it will be very hard to know what to do next.

Hyper-space planes : the Virtual Observatory. As we explore the various possible axes one by one, many if not most of them are running out of steam, or are too expensive to pursue. But we are a long way short of exploring the whole space – for example narrow line imaging in all Stokes parameters versus time. This exploration does not necessarily need complex new experiments. More survey-quality datasets come on line every year. As formats, access and query protocols, and analysis tool interaction protocols all get standardised, the virtual universe becomes easier for the e-astronomer to explore, and unexpected results will emerge. This, of course, is the agenda of the worldwide Virtual Observatory initiative.

So there we have it. The fify-something Prof’s recommendation for the eager young survey astronomer : time, neutrinos, and the internet.


The man who measured the size of the Universe

April 14, 2007

Last night I was faced with a mixture of achievement and failure, wonder and decay, drinking tea in the room where Thomas Henderson calculated the distance to the stars.

I was giving a talk to the Astronomical Society of Edinburgh, a long established amateur society. My talk was about mapping the Universe, first stepping through the history, and ending up with modern results from SDSS, 2dFGRS, and UKIDSS. I mentioned Thomas Henderson, my predecessor as Regius Professor; a great hero, as in 1833 he was the first man to measure parallax and so determine the distance to a star (Alpha Centauri). He made the measurements in South Africa and finished the calculations in Edinburgh. Alpha Centauri is the very nearest star system; but it is almost seven thousand times further away than Pluto… The universe of stars is unimaginably vast.

I showed a picture of a memorial to Henderson Thomas Henderson Memorial on Calton Hill Edinburghwhich I had found on the web, and mentioned that I wasn’t sure where it was – maybe in the same cemetery as David Hume ? Oh no, they piped up – its on the side of this building ! (And the image came from their website… oops.) The ASE are lucky enough to use as their HQ the old City Observatory on Calton Hill, where the Astronomers Royal worked until 1894 when the new Royal Observatory was built on Blackford Hill on the outskirts of Edinburgh. (This is where I work now of course..). Well…I say lucky, but the state of the buildings is a scandal. They are owned by the City, but gradually decaying. The toilets don’t work, and the ASE guys warned me to go before I turned up.

After the talk they fed me tea and biscuits in a room where they reckon Henderson did his calculations after returning from the Cape. But its also where he lost his nerve. In the 1830s measuring parallax was the big prize, and some people had had egg on their faces -Henderson was nervous about whether he had got it right, and didn’t publish. Finally in 1838 Friedrich Bessel beat him to it and published the parallax of 61 Cygni. Henderson finally published the next year. His distance was right within about 30%.

So on the way out I walked around the side of the beautiful Playfair building. Fog was swirling around the walls (no observing last night !). ASE scretary Graham Rule shone his torch for me, and there it was – a modest monument to the man who showed just how big the Universe really is.


UKIDSS marches on

March 2, 2007

Yesterday saw the second data release (DR2) of the UKIRT Infrared Deep Sky Survey (UKIDSS), the biggest infrared sky survey so far. The UKIDSS home page is here, but you get the data from the WFCAM Science Archive (WSA).

I am the PI of the survey, but lots of other people do more work than me – especially Survey Scientist Steve Warren, who is the lynchpin of the whole thing, and Nigel Hambly, who masterminds the WSA. Nige is the one who has been losing sleep getting ready for the release..

This event put me in mind of a strange day a year back when I went out to Hawaii to do a UKIDSS observing run, and got stuck into a five hour conversation about science and religion. I would have expected this to irk me, but in fact it was fascinating .. I will try to write this up over the weekend…


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