SKA: a step closer

In my last post I talked about improvements in astronomy (especially radio astronomy) over the past 60 years. Looking to the future, the next big thing in radio astronomy will be the Square Kilometre Array (SKA). Unsurprisingly, it will consist of a square kilometre of collecting area, but rather than be in one single dish (which is a bit impractical from an engineering point of view) it will be made up of lots of smaller dishes spread over a gigantic area. This is a truly huge project which no one country can do alone, so it is being developed by astronomers and engineers from all over the globe. It is planned to be constructed around 2015 and should push the sensitivity of radio astronomy up by another factor of 10 compared to the EVLA and eMERLIN which will be coming online in the next few years.

The eventual location for this huge project has, finally, been narrowed down to shortlist of two: South Africa (and surrounding countries) and Australia (and possibly including New Zealand).
So why are these two the best places on Earth? Well, there are a couple of reasons. First, both of them are in the southern hemisphere at a latitude which lets you look at the most interesting parts of the sky. Not only do you see some of the northern hemisphere but you can easily see the most interesting parts of our galaxy (like the centre) as well as our neighbouring galaxies the LMC and SMC. The second reason is that in other places there are too many people; folks like you and me. Where people live, mobile phones, Wifi networks, TV, radio stations and other sources of radio waves have a tendancy to follow. If you are going to build a stupendously sensitive instrument, you had better put it in a very quiet environment in the same way that big optical telescopes get built a long way from towns and cities that light up the night sky.

Both Australia and South Africa are ideal for the SKA because they have deserts with large areas with low population densities and that isn't likely to change too much in the next 20 years or so. Which will come out as the final site remains to be seen (although not before 2010) and may end up being decided by politicians rather than on the basis of science.

What could come after the SKA? A radio telescope on the far side of the Moon perhaps?

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Posted in astro blog by Stuart on Friday 29th Sep 2006 (13:25 BST) | Permalink

Size matters

With telescopes, the diameter matters. Bigger is better in two ways. First of all, the wider the telescope, the more photons of light (or radio waves/X-rays/whatever) it can collect and the more photons the better the quality of the images or measurements. That is called the sensitivity and can be thought of as the number of grey-scale levels in your image. Secondly, due to the physics of optics, the larger the diameter of your collecting bucket, the better the resolution; the image looks less blurry. For instance, a 10 inch (25cm) diameter optical telescope can theoretically tell apart two stars that are spaced by only half an arc second (a 6500th of a degree). In reality, our atmosphere smears everything out so you don't actually get images as good as that. Pity!

For optical telescopes, the atmospheric smearing (or 'seeing') meant that improvements in resolution were limited until the Hubble Space Telescope (HST) in the 1990s when, for the first time, a telescope could get a perfectly clear view (that is one of the reasons Hubble has done so well). However, throwing enough clever people at the problem of 'seeing' has meant that in the last few years fancy techniques like adaptive optics are starting to give images from the ground that are nearly as good (or better) as those from space. The next steps in optical astronomy should see the launch of the next-generation HST (named the James Webb Space Telescope) and the construction of 30-100 metre diameter optical telescopes. That would be a sight to see!

But astronomy isn't just about optical telescopes. Over the past 60-70 years radio astronomers have been steadily improving the quality of their observations of the Universe too. Nowadays, radio telescopes are often linked together to make an instrument the size of our planet (VLBI), so the resolution has got about as good as it can get unless we build radio telescopes elsewhere in the solar system and that is a tad expensive just now. So, the next step in making radio telescopes better is to improve the sensitivity.

The first purpose-build radio telescope was built in 1937 in the back garden of Grote Reber who lived in Chicago. It was nine metres in diameter which is pretty big for a back garden. After those initial observations, no major new instruments were built until the 1950s with the construction of Dwingeloo in the Netherlands and Jodrell Bank in the UK. With much larger areas, these instruments were 10s to 100s of times more sensitive than Grote's first dish so could do better measurements. Progress has continued at a tremendous pace over the 1960s (Parkes, Arecibo and Effelsberg), 1970/80s (VLA, ATCA), and up to the present day (GMRT, GBT) each time, increasing the sensitivity. Today, the most sensitive radio telescopes are about a few hundred thousand times more sensitive than the state of the art in 1937. This rate of improvement is pretty impressive and in the next few years eMERLIN and EVLA will push that up to a million times more sensitive than we were in 1937 (see plot below and be amazed). Although bigger and better usually means more money and more difficult, plans for the next-next generation are already under way. More on that in my next post.

Sensitivty
The sensitivity of radio telescopes since 1937 CREDIT: Square Kilometre Array website

Posted in astro blog by Stuart on Friday 29th Sep 2006 (13:06 BST) | Permalink

Young Galaxies

A few years ago (around 1995) the Hubble Space Telescope stared at one apparently empty part of the sky in Ursa Major for around 125,000 seconds in order to look for very faint objects. The resulting Hubble Deep Field (HDF) through up a few thousand beautiful galaxies that nobody had seen before. A few years later, in 2004, the Hubble Ultra Deep Field (HUDF) was released which did a similar thing but had a total exposure time of around 1 million seconds. Just think about that for a moment; that is about 11 and a half days solid staring at the same point. Needless to say, it makes a pretty spectacular image.

Now, astronomers analysing the HUDF have identified over 500 galaxies that we see at a time when the Universe was less than a billion years old. That may seem like quite an age but compared to the current age - 13.7 billion years - that is effectively the early childhood of the Universe. These galaxies tend to look like rather unexciting red blobs but are actually very blue dwarf galaxies with lots of stars being formed within them. They appear red in the Hubble images because their light has been redshifted by the expansion of the Universe in the 13 billion years or so that it took the light from them to reach us.

HUDF
Hubble Space Telescope image showing 28 of the more than 500 young galaxies that existed when the universe was less than 1 billion years old. CREDIT: NASA, ESA, R. Bouwens and G. Illingworth (University of California, Santa Cruz, USA)

The measurements also show that there was around 10 times the amount of star formation back then as we see in nearby galaxies today. That suggests that there may have been enough light being emitted to reheat the hydrogen gas that had been cooling since the big bang.

Hubble continues to produce lots of great science so I just hope the Hubble servicing mission goes ahead to keep things going until the James Webb Space Telescope is launched.

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Posted in astro blog by Stuart on Thursday 21st Sep 2006 (19:34 BST) | Permalink

Atlantis back safe

As Tom reports, over the past couple of hours the space shuttle Atlantis made its way back through the atmosphere. Its route brought it over central America and the Gulf of Mexico towards the landing site in Florida. What I always find suprising is the steep angle of approach as Atlantis nears the runway; I'm told that it is about 21 degrees which is steeper than you would see with a jumbo. Anyway, the important thing is that touchdown was successful.

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Posted in astro blog by Stuart on Thursday 21st Sep 2006 (11:26 BST) | Permalink

Low density planet found

A team of astronomers using the Hungarian Automated Telescope (HAT) network have identified what may be the least dense planet that we know of. According to their measurements, the planet - with the catalogue name HAT--P-1b - has an average density of about 0.3 that of water (at 1 atm and room temperature). That makes it less than half the density of the planet Saturn and is similar to the density of a sponge cake. That is very dilute indeed.

The HAT network (named HATNet which makes me think of old ladies and hair nets) consists of six small automated telescopes; four at the F. L. Whipple Observatory in Arizona and two at the Submillimeter Array on Hawaii. Each of these observes an 8 by 8 degree patch of sky looking for changes in brightness of the stars it is observing. Occasionally, just occasionally, one of the stars will have a dip in its brightness because a planet comes between us and the star during its orbit. (You may have been lucky enough to see the effect of a transiting planet for yourself with the transit of Venus a couple of years ago.)

ADS 16402B
Image of stars ADS 16420A and ADS 16420B taken with the F.L. Whipple Observatory 1.2m telescope. CREDIT: Bakos et al astro-ph/0609369
In this case, the star in question is one of a binary star system - ADS 16402A and ADS 16402B - in which the stars are separated by about a fortieth of a light year (1550 AU). The star that the planet orbits is about 10th magnitude and a little larger than our Sun. Interestingly, the discoverers investigations have shown it to have extremely similar properties to its binary companion making the calibration of their measurements easier.

So, roughly every four and a half days ADS 16402B gets a little dimmer as the planet passes in front of it and the team were able to measure five of these transit events during their observations. Once they had worked out the time for one orbit (4.5 days) they were able to calculate the distance of the planet is from its star. At the same time, measurements of the reduction in light from the star let them work out how big the star is (1.4 times the size of Jupiter) as larger planets block more of the light from the star. Now, to work out the density they used one last trick; they got the mass of the planet by watching how it makes the star wobble. The size of the wobble is related to the distance between the star and the planet and the mass of the planet. So you can work backwards and get the mass of the planet knowing the separation from the star and the size of the wobble from measurements of the speed of the star. Doing all that showed that the planet has a very low density. Pretty neat eh?.

But a planet as dense (or rather sparse) as a sponge cake throws up some other questions. Why is it so puffed up? Could it be because it is heated up by its star as it is pretty close to it after all? Well, the paper's authors don't reckon so because you would expect other 'hot Jupiter' planets to have the same effect and that isn't seen. They actually reckon that it is being heated from the inside by tidal heating because its orbit isn't perfectly circular. What makes it slightly elliptical in this case is another question and they suggest that there may be another planet in the system that is perturbing the one they found. Whatever the case, it is certainly an interesting bit of detective work.

Posted in astro blog by Stuart on Sunday 17th Sep 2006 (16:02 BST) | Permalink

Slacker Astronomy the end?

There are certain radio programmes that I will listen to regularly as a loyal listener because they make me laugh or are interesting and thought provoking. In the last few years I have expanded my list of favourites to take in more radio programmes from around the rest of the planet Earth. I especially listen to those that are podcast as I can save them and listen to them away from my computer. The podcast revolution has not just allowed traditional radio stations to reach a wider audience; it has allowed the rest of us to add content and style to the mix on topics such as astronomy.

For me, the first true astronomy podcast was Slacker Astronomy which started in February 2005. Others have claimed to have been going longer but I suspect that was only by adding a back catalogue of existing radio programmes. Nevertheless, it was the first that I became aware of in early 2005. Since those early beginnings they have had, by my estimation, 69 main shows, 10 chit-chat shows and 25 assorted others. With their weekly mix of stories and a lighthearted approach (some would say cheesy but of course I won't say that) they reached regular audiences of around 15,000 listeners, and were often ranked in the top 25 Science podcasts in Apple's iTunes directory. They were living the dream of astronomy super-stardom. But now the dream is over. Slacker Astronomy is no more.

This is starting to sound like an obituary. Is it really the end? Well, no. Slacker Astronomy has just broken up into mutant astronomy offspring including two podcasts and a Wiki. Pamela has gone her own way and teamed up with Fraiser Cain of Universe Today to make a new podcast named AstronomyCast and they have a show out already. The rest of the Slacker Team, along with some of the occasional guest presenters, are reforming to make a new monthly hour or two long podcast which will be a mix of the old show and the chit-chat shows (the format sounds strangely familiar!). Oh, and they have come up with a new name: Slackerpedia Galactica. I assume that the name is to make people think of the Encyclopedia Galactica in Issac Asimov's Foundation or the one with the same name in the Hitch Hiker's Guide to the Galaxy.

Whatever happens to Slacker Astronomy derivatives in the future, I hope they speed up their servers a bit.

Posted in astro blog by Stuart on Friday 15th Sep 2006 (17:01 BST) | Permalink

Eris and Dysnomia

The object 2003 UB313 now has a name. Thank goodness for that. We can now start calling it Eris - a Greek goddess of discord and strife - which is quite appropriate given that 2003 UB313 Eris caused the definition of a planet to be brought into question over the last couple of years. It has taken this long for the name to be assigned because the status of the object - which is slightly larger than Pluto - had to be confirmed so that the appropriate naming committee of the IAU could decide. The new name is pronounced ee' ris and was suggested by its co-discoverer Mike Brown.

Eris's moon (previously nicknamed Gabrielle) has been named Dysnomia - the Daimon spirit of lawlessness - which may be playing on the surname of the actress that plays the character Xena (also Eris's nick name for the past year). In the Greek myths, Dysnomia was the daughter of

Eris and the counterpart to Eunomia who

puts an end to the anger of grievous strife.

We still have to wait for names for the other potential dwarf planets: 2005 FY9 and 2003 EL61.

Posted in astro blog by Stuart on Thursday 14th Sep 2006 (18:15 BST) | Permalink

NZ Meteor

I've just got a message, via the family grapevine from my cousin (via my auntie and my dad), of a meteor hitting a farm near Christchurch in New Zealand. My cousin, along with plenty of other people from Ashburton to Wellington and Wairarapa reported a loud sonic boom and a large fireball. The New Zealand Herald has plenty of eyewitness reports (should that be earwitness?).

Strangely, the Bad Astronomer just had a post about a meteor over Western Australia last December.

Posted in astro blog by Stuart on Tuesday 12th Sep 2006 (16:41 BST) | Permalink

Lunar Eclipse

Last Thursday night there was a partial lunar eclipse. Will Gater (regular contributor to Astronomy Now) got some nice images of it from Torquay in Devon. By the way, he gets some dark skies down there on Dartmoor and he takes some really nice photographs of things like the Milky Way, the Summer Triangle and the Moon which are well worth checking out. If you live down (or up!) that way, you may want to have a look at the Torbay Astronomical Society website too.

Posted in astro blog by Stuart on Monday 11th Sep 2006 (00:09 BST) | Permalink

Aurora from above

The northern or southern lights are a beautiful sight to see. Here is a lovely picture of the Aurora Australis (southern lights) seen from a rather unusual angle; looking down. The image was taken on 30th May 2005 from the International Space Station whilst it was passing over the Bass Strait in the southern Pacific. You can even see some star trails through it!

Aurora Australis
Aurora Australis seen over the Pacific Ocean from the ISS. (ISS011-E-7595). CREDIT: Image Science & Analysis Laboratory, NASA Johnson Space Center.
The aurora are caused when charged particles from the Sun hit oxygen and nitrogen atoms in the Earth's atmosphere and cause them to emit light. There tends to be more nitrogen than oxygen lower down in the thermosphere (say lower than 150km) and so colours due to nitrogen (red, blue and violet) tend to originate from there. The common green colour of aurora (and the only one I've seen) is due to oxygen atoms and occurs from altitudes between 100km and 300km. The less common red oxygen colour occurs at much higher altitudes - 300km to 500km - because the nitrogen density needs to be low for that type of emission to occur.

The crew of the International Space Station have taken many wonderful images of the aurora from their vantage point at about 370km altitude. Sometimes the crew have even found themselves in the "dimly glowing fog of red". Although that is an awe inspiring experience, there must be a bit of a worry about being amongst all those high-energy particles from the Sun.

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Posted in astro blog by Stuart on Saturday 09th Sep 2006 (20:03 BST) | Permalink

Atlantis on the pad

The Space Shuttle Atlantis is getting ready for launch at about 11:50 EDT following some delays. Currently, they have cleared a problem with fuel cell 1 but there is a problem with a fuel cut-off sensor. NASA TV have a webcast of the launch build-up for those of us that can't pick it up via satellite. You can also follow what is happening in NASA's live Launch Blog. Seeing the Shuttle on launch pad 39-B is an amazing sight.

Hopefully in a few days, the International Space Station will have a new solar array. Good luck Atlantis.

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Posted in astro blog by Stuart on Friday 08th Sep 2006 (15:30 BST) | Permalink

A landmark

For the last few weeks the BBC News website has been running an online vote to find the UK's most popular 'unsung landmark'. Amongst the finalists were the Humber Bridge, the New Severn Crossing and some airship hangars. The vote closed on Wednesday last week and by Thursday afternoon it became apparent that the 76m Lovell Telescope at Jodrell Bank Observatory had won. It isn't often that a scientific instrument wins such a competition.

If you haven't heard about it before, the Lovell Telescope was probably the UK's most famous involvement in the space race (there was a fairly successful rocket programme with Australia but most people have never heard of that) as it was the only place in the world that could track the carrier rockets that launched Spunik in 1957.

Last Friday, a reporter from the BBC website turned up (complete with shorthand covered notepad) to interview some of the staff and members of the public in the visitor centre. The final article has just appeared on the BBC News Magazine site with a nice review of the science that the telescope has done (and still does) as well as some more aesthetic comments about the structure.

Posted in astro blog by Stuart on Tuesday 05th Sep 2006 (13:23 BST) | Permalink

Moon rising

SMART-1 crashed into the Moon this morning. The Moon was unfortunately below the horizon in the UK at the time, but this afternoon I got a nice view of our largest satellite from the seaside at Bridlington. It was cool to think that just a few hours before, a spacecraft had crashed into it (the Moon that is, not Bridlington!). Some animations and images are now starting to appear on the web (via Ian).

Moon and sea
The Moon seen from Bridlington, UK on 3rd September 2006 CREDIT: Stuart

Posted in astro blog by Stuart on Monday 04th Sep 2006 (01:04 BST) | Permalink

SMART-1: the last hours

The last few days appear to have been quite exciting for the SMART-1 team. Stereo imaging by the spacecraft during the week helped the team get a better idea of the height of the terrain surrounding the nominal impact site and they planned to fire the thrusters to boost the final orbit. However, in a senario that makes me think back to the unlucky Hayabusa, a fault caused SMART-1 to put itself into safe-mode on 1st September. This meant that the spacecraft had stopped normal operations and was waiting for reset commands. Thankfully, within six hours ESA's Spacecraft Operations Centre (ESOC) had managed to get SMART-1 back online. It sounds like a nail-biting time in ESOC (which you can watch on their webcam although right now it is pretty quiet)

Tonight, the mission scientists should be receiving the last data that the spacecraft will transmit before its expected impact at 05:42 UT this morning (Sunday 3rd September). If you have binoculars or a small telescope and live in the western parts of North or South America you can try to observe the impact yourself. Here in the UK (and Europe) we won't see anything because we are facing the wrong way.

Farewell SMART-1.

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Posted in astro blog by Stuart on Sunday 03rd Sep 2006 (01:17 BST) | Permalink

Gemini South

Astronomy Picture of the Day (APoD) showcases some stunning images. Today's image shows star trails and the Gemini South telescope. The star trails appear because the exposure was about (by the looks of it) two hours long and the rotation of the Earth makes the stars appear to move across the sky. As a result, all the stars appear to turn around the points above the poles of the Earth. In this case the observatory is in Chile so all the stars appear to rotate around the point above the south pole - just off the left of this image. You can also see the Large and Small Magellanic Clouds (two dwarf galaxies) smeared out during the exposure in the top left and there is even a meteor streak visible. Beautiful.

 Gemini South Star Trails
Star trails seen with the Gemini South telescope CREDIT: Elke Schulz

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Posted in astro blog by Stuart on Friday 01st Sep 2006 (17:06 BST) | Permalink

Uranus and Ariel

Just in case you haven't been keeping up with other astronomy blogs (shame on you if you haven't!), check out Tom's Astronomy Blog as he features a great Hubble Space Telescope image of the planet Uranus along with one of its moons Ariel (and the shadow of Ariel). It is a really great image.

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Posted in astro blog by Stuart on Friday 01st Sep 2006 (16:50 BST) | Permalink

SMART-1 impact

As mentioned by several other people, ESA's SMART-1 spacecraft will be crashing - in a deliberate way - onto the surface of the Moon on 3rd September. The exact time of the impact isn't certain because it depends on the exact heights of the lunar mountains. So, there are three orbits on which it may crash. The first has its closest approach at 00:37 UT, the second at 05:42 UT and the third at 10:47 UT on 3rd September. The nominal time for the impact is 05:41 UT. I made some finding charts for the Jodcast to give a rough idea of where to look. There is a whole Moon chart (made using Stellarium) and a closer in chart (made with NASA's WorldWind) showing the impact sites with respect to the crater Tycho. Of course, they are my impression of the positions taken from the rather small ESA images from a day or two ago. Now, ESA have a great image of the impact sites taken by SMART-1 itself on their website.

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Posted in astro blog by Stuart on Friday 01st Sep 2006 (15:39 BST) | Permalink
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