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A comedy series about an astronomer..?
Yes, you read that right. This year I failed to escape the dreaded fresher's flu so I'm sat drinking tea and eating oranges in front of the TV. I am actually doing some work, writing some observing proposals for the next VLA deadline which is Monday. Anyway, between progams on BBC2 there was an advert for a new comedy series about an astronomer! The show is called "Supernova" and features Rob Brydon as an astronomer in the Australian outback at the (fictional) Royal Austrlian Observatory. There is a press release about it on the BBC's website so you can check that I'm not making it up.
Posted by Megan on Friday 30th Sep 2005 (21:16 UTC
) | 7 Comments
Upcoming Solar eclipse
This coming Monday (3rd October) there will be an annular eclipse of the Sun. The path of totality passes over Spain and parts of North and East Africa. Lot's of information, including maps of the totality track and timings of the event for various locations around the World, can be found on Fred Espenak's pages at NASA.
During totality in a normal eclipse the Sun is completely hidden. It goes very dark and the corona (the gas around the Sun) can be easily observed. An annular eclipse, however, is one where the Moon is just far enough away from the Earth that it doesn't quite cover the disk of the Sun completely. In this kind of eclipse it doesn't go as dark and the thin ring of the Sun's disk still visible is bright enough to completely wash out the corona.
At Jodrell Bank Observatory we are observing the event, assuming the weather cooperates of course! From the latitude of the Observatory (~53o), the Moon will cover approximately 60% of the Sun's disk at mid-eclipse so we do not see a full eclipse. From our location, first contact, the time when the Moon appears to start cutting in to the Sun's disk, is at 08:49 BST. Mid-eclipse occurs at 10:00 BST. Fourth contact, when the Moon's disk leaves the Sun completely, is at 11:14 BST. At Jodrell, the visitor centre will open at 08:30 BST on the day, earlier than usual so that we don't miss first contact. There will be a talk about eclipses by an astronomer from the Observatory, telescopes set up so visitors can safely view the eclipse by projection (never use a telescope to look at the Sun!), trips to Mars in the 3D theatre, and Ask an Astronomer sessions. If you happen to be nearby, come along and say hello.
Posted by Megan on Wednesday 28th Sep 2005 (21:41 UTC
) | 2 Comments
Orion from my window at about 5am, 26 September 2005 CREDIT:
I've not had much sleep in the last few days for a couple of reasons. On Sunday I went to bed quite late, then woke up two hours later. Normally, when I wake up, the first thing I do is peek through the curtains to see what the sky looks like. On this particular morning the sky happened to be clear and the atmosphere was quite still (for Manchester). When I pulled back the curtain I saw the constellation of Orion perfectly framed by the surrounding buildings.
You know the year is moving on when Orion starts to be visible again. Just like the bright stars of Cygnus, Lyra and Aquila (which define the Summer triangle) are prominant in the summer months, Orion dominates the sky throughout winter.
So, as I was wide awake by this point, I got out my little digital camera and took a few pictures. As my big tripod is at work (for use with the solar telescope), all I had was a tiny table-top tripod. The image on the left is a composite of two frames taken at about 5am with the camera balanced on the top of a box turned upside down on the end of my bed. The leaves in the foreground are the plants on the windowsill, and you can see the orange glow near the bottom of the image due to the streetlights of south Manchester.
Posted by Megan on Wednesday 28th Sep 2005 (18:41 UTC
) | 2 Comments
I've finally got round to finishing off and putting online some of the astronomical activities I've had lying around for ages. There is an activity illustrating Hubble's Law with real data which was used with gifted and talented children back in May. They got the hang of it, but it is really more appropriate for older children. There is also a hands-on activity to build a Martian rover out of ordinary household objects. There is a sheet for the students with some ideas, and one for the teacher with some more information on real rovers. All these are linked from the resources page.
Posted by Megan on Sunday 25th Sep 2005 (09:08 UTC
) | 6 Comments
AAVSO surveys amateurs
Today's quick link on astro-ph is by Aaron Price (of Slacker Astronomy fame) and colleagues at the AAVSO and Space Sciences Laboratory at the University of California. The paper, published in the AAVSO's journal, describes a survey of amateur astronomers to determine what the National Virtual Observatory could be doing that would be of use to the community. This goes back to the letter in Astronomy Now back in July asking if there was any point to amateur observing any more: the AAVSO maintains a database of observations of variable stars containing over 11 million entries, most of which have been made by amateur astronomers.
The paper describes the survey which was carried out, the results that came from it and some recommendations for the AVO. One bit that made me laugh was the breakdown of astronomers into five groups: Romantics (a.k.a. armchair astronomers), Educators (teachers or those who do public outreach), Serious Visual Observers (who do Messier marathons for example), Serious Imagers (like those who hunt supernovae), and Tinkerers (prefer to build or modify their own equipment). Macclesfield Astronomical Society has plenty of each!
Posted by Megan on Thursday 22nd Sep 2005 (23:49 UTC
) | 4 Comments
Earlier this week I went to Leicester University to visit the UK Swift team and learn how to analyse data from the Swift satellite. It was fun and I learned a lot, but there was too much to take in in one day.
Swift has three instruments onboard which are co-aligned, they all point at the same patch of sky. The first of these is the Burst Alert Telescope (BAT), a gamma-ray detector which observes a large part of the sky at once (it has a field of view similar to your eye) looking for new burst events. Within seconds of detecting a burst, the instrument provides the position of the event to an accuracy of four arcminutes which is then passed to the X-Ray Telescope (XRT) which has a smaller field of view than the BAT but can provide positions to an accuracy of five arcseconds. The final instrument is the Ultra-Violet and Optical Telescope (UVOT) which has an even smaller field of view but can provide a position accuracy of less than an arcsecond.
The satellite generally operates in "survey mode". In this mode, astronomers can suggest targets for observation. For example, if you look down the list of recent targets on the quick look site you may see some targets that begin "SN", these are supernovae which have been observed by Swift. Looking on there today they have recently observed: SN2005df, Tempel 1, Mrk684, Abell2029 plus a whole bunch of GRBs. But when a GRB occurs in the field of view of the BAT it enters what is called "burst mode". If the burst was significant (had a high enough "merit") to trigger burst mode, the position provided by the BAT is passed to the satellite control software which automatically causes the Swift to slew to the position which enables the use of the more accurate XRT and UVOT instruments.
For each burst there is plenty of data to look at. There is gamma ray data from the BAT, X-ray data from the XRT, and UV and optical data from UVOT. Each instrument provides both images and spectra of each event which can be used to characterise the bursts. This all helps with GRB research: the more data we have on these energetic events the better we can constrain the models and work out just what is going on to produce such intense bursts of radiation.
Part of our training involved actually using the software to analyse archive data from each of the instruments. Unfortunately we didn't have time to get through all of the tutorials but when I have some spare time I will install the software, finish the tutorials and post some pictures. In the mean time, if you are interested in some more technical details try the following pages at Nasa's Goddard Space Flight Centre: BAT, XRT, UVOT.
Posted by Megan on Wednesday 21st Sep 2005 (23:56 UTC
) | 4 Comments
Over the weekend I visited my Dad at the house he and Sar now own in Scotland. It's in a small fishing village on the coast about two hours drive north of Aberdeen, and a long way from the nearest town so the skies are pretty dark. After all the solar activity recently we were hoping for clear skies, but we should have known better, Scotland is not renowned for good weather! With the full Moon the sky looked like dawn for most of the night so there was no chance of seeing anything, even if the cloud had evaporated. Still, it was a nice weekend. I gave my four year old niece a belated birthday present as well. She got a book about the man who entertains the tourists on the Moon, and some glow-in-the-dark stars and planets. :-) She is very lucky growing up in a place like that. The scenery is amazing up there and, despite the cloud, the sunsets are pretty amazing. If there was an observatory up there, I'd move.
Posted by Megan on Monday 19th Sep 2005 (20:40 UTC
) | 10 Comments
Yet more sunspot images...
Today I borrowed a camera and had another go at imaging the Sun. Above you can see the results, click for larger versions. Several prominances are visible around the edges, and some detail is visible in the sunspot complex itself. The camera was a Kodak with 3.1 megapixels compared to my Nikon with 2.1 (which I used to take the previous images), and it also has better zoom capabilities which helps. The levels of all of these images have been adjusted to bring out a bit more detail, but no other fudging of the data has occured. Promise.
Posted by Megan on Wednesday 14th Sep 2005 (21:22 UTC
) | 8 Comments
Images taken using the Faulkes Telescopes CREDIT:
Faulkes Telescope Project
Today the building was full of teachers who were here on a training course. They were learning how to use the Faulkes telescopes
, a pair of 2-m telescopes, one situated in Hawaii, the other in Australia. They can be used by school teachers in lessons to show children the planets, comets, galaxies, pretty much anything you want to look at in the sky (except the Moon - it's too bright!). Their locations mean that when it is daytime here in the UK, it is night time at the telescopes so they can be used in normal lessons.
Back in January this year several of us used the Faulkes Telescopes at a nearby school to image a variety of objects. It was quite scary doing this live in front of a hall full of children having never used the telescopes before! The weather caused us problems too as it was unseasonably cloudy on Hawaii. We did get some good results though, and some of them can be seen on the left. Click on them to see larger versions.
After the teachers left, I went to speak to the people from the FT project who were running the training course about their science projects that are available for schools. It sounds like things are going well for the project at the moment and the training courses are in demand from teachers around the country. They have some big news too: a new sponsorship deal! This will mean that the telescopes will be available free to schools in the near future. But I can't say any more (ooooh, suspense!), mainly because they wouldn't tell me any more. There will be a press release on Monday though, so we'll all have to wait until then to find out who the mysterious benefactor is. Any guesses?
Posted by Megan on Wednesday 14th Sep 2005 (18:26 UTC
) | 4 Comments
More sunspot images
Here is an image of sunspot group 798/808 taken today at around 14:30 GMT today. Although still not a great quality image, you can see more detail in the complex in this image - it really is amazingly huge. The major prominance of yesterday has shrunk quite a bit, but there are several other impressive ones to look at.
The Sun in H-alpha light on 12th September 2005 CREDIT: Dave
/ Megan (one of us took it, not sure who!)
One thing I have to stress is that you should NEVER
look at the Sun through any kind of optical aid: telescopes, binoculars, or any kind of magnifying lens. Really you should avoid looking at it using just your eyes. It is very bright and very hot and you WILL
damage your eyes if you try it. The only really safe way to view the Sun is by projection. The folks over at the BBC have some useful tips
on how to view an eclipse safely which apply just as well to the Sun normally.
This image was taken using a special telescope which uses some fancy optics to block out 99.999... per cent of the Sun's light. The image is red because the only light that gets through is in the red part of the spectrum at a wavelength of 656 nanometres, a particular colour of light which is emitted by the hydrogen atom. This allows you to see more details on the surface of the Sun than you can with white light. The view through the eyepiece is far more spectacular than these images but, unfortunately, my camera is just not good enough to image it. Much better images can be found over at SOHO.
Posted by Megan on Tuesday 13th Sep 2005 (23:32 UTC
) | 2 Comments
Sunspot group 798
The Sun in H-alpha light on 12th September 2005 CREDIT:
Wow, this sunspot group is huge
! As Macclesfield Astronomical Society's solar telescope is sat under my desk at the moment I thought I would have a look. This image was made by holding my little digital camera to the eyepiece of the telescope so it isn't as well focused as it could be, but it's not bad. There is a large prominance on the edge of the Sun on the right hand side of the image. To give you some idea of the scale, Earth would be dwarfed if you put it next to the prominance.
Posted by Megan on Monday 12th Sep 2005 (16:28 UTC
) | 2 Comments
Swift's most distant burst yet
The Swift satellite CREDIT:
In the 1960s, satellites designed to monitor compliance with the nuclear test ban treaty discovered peculiar bursts of radiation coming from outside the Earth. Nuclear explosions produce bursts of gamma rays (photons of light with very short wavelengths) so these satellites watched the surface of the Earth so that if someone broke the treaty and exploded a nuclear bomb in secret it would be detected. What they discovered instead were bursts of gamma rays coming from the sky. The bursts were distributed randomly which immediately ruled out some ideas about where they might come from. If they came from nuclear explosions on Earth, you would only detect them while pointing at the Earth. If they came from our Galaxy then you would see them in a thin strip across the sky corresponding to the disk of the Milky Way. As the distribution was random either the cause of the bursts had to be very local (within the solar system) or very distant (distributed throughout the whole universe).
Astronomers used to favour the nearby hypothesis because of their enegy output. The energy from a source decreases according to the inverse square law, light spreads out as it moves away from a source, so a distant object must be much brighter to appear the same as a nearby object (think about car headlights). Astronomers now think that these objects are very distant. One reason for this is that often these GRBs leave optical afterglows which fade much slower than the initial gamma ray burst and can be detected by ground-based observatories. By using optical telescopes astronomers have managed to take spectra of some of these optical afterglows and determine from their redshifts that they are distant objects. So, although they are not caused by nuclear weapons, they are caused by massive explosions. Models of GRBs suggest that they are far more energetic than supernovae which are pretty big explosions themselves.
The initial bursts are still hard to detect though. Gamma rays do not pass through the Earth's atmosphere very easily so detectors are still sent into space on satellites. One of these, the Swift satellite, was launched in to low Earth orbit aboard a Delta rocket in November 2004. Since then it has detected many bursts. Each time one is found an alert is sent which allows optical observatories to rapidly make follow-up observations to look for the optical afterglows and hence find distances to these objects. As well as the alerts, the team also provide a map of recent bursts which is pretty cool.
The burst profile of GRB 050904A from Swift CREDIT:
Swift / NASA
On September 4th 2005, the Swift satellite detected another burst of gamma rays from the distant universe: 090504A (first reported in GCN 3910). This burst is noteworthy because it might be the most distant GRB ever detected. It was also one of the longest, lasting 120 seconds (I told you they were short!). The image on the right shows the light curve, how the brightness of this burst varied with time. Although optical telescopes looked for an afterglow, 050904A was not detected optically, but it was detected at slightly longer wavelengths in the infra-red part of the spectrum. This difference could be due to obscuring dust in the host galaxy which would absorb optical but let through infra-red light, but other parameters determined from the observations would appear to rule this out. The other possibility is that this could be a very distant explosion, the observations would imply a redshift, z, of between 6 and 8 which corresponds to a distance of between 12.7 and 13 billion light years.
On Monday 12th September 2005 NASA will host a press conference on this burst at 2 pm EDT which will also be webcast on NASA TV. Participating scientists will include Neil Gehrels, Swift principal investigator at NASA's Goddard Space Flight Center. Should be interesting.
Posted by Megan on Sunday 11th Sep 2005 (17:58 UTC
) | 24 Comments
Festival of Science 2005
It has been a busy week for meetings and cenferences. From September 3 - 10 the city of Dublin hosted the 2005 BA Festival of Science. These fesivals have very varied programmes including lectures on a variety of topics, activities, workshops and lectures for the public. This year some of them were broadcast live over the web. One topic at this year's festival was encouraging children to develop an interest in science and technology. There are many initiatives to encourage scientists to communicate with the public in general, but Sir Roland Jackson, the Chief Executive of the BA, has commented that it is important to listen to what issues are important to young people so that we can show them how science and technology is relevant to them. Young people have been involved with the Festival as well: on the Wednesday a group from a local youth theatre created and performed a piece based on various physical theories: the model of the atom, nuclear fission, and state changes from solid to liquid to gas. The BA article on this event syas that the performance was so good, the audience ended up feeling sorry for an atom! Next year the Festival will be in Norwich and the theme will be People, Science and Society.
Posted by Megan on Sunday 11th Sep 2005 (11:49 UTC
) | 3 Comments
It's not just students that seem to spend their time blogging - some lecturers do it too. Andrew Jaffe, an astrophysicist at Imperial College London, also has a blog. On Friday he wrote about this comment piece in the Guardian by Paul Davies, a physicist at the Australian Centre for Astrobiology (ACA) at Macquarie University in Sydney. I missed this one altogether as it was in the main paper which I rarely read. Unfortunately, this was the last time I will bother with the Guardian anyway, as they have decided to get rid of the excellent Life section, the only science supplement I know of.
In his article, Prof. Davies talks about the chances of life evolving which, even when all the required ingredients are present, are very small. But he phrases it as being "virtually zero" and then goes on: some sort of “life principle” is envisaged to be at work in the universe, coaxing matter along the road to life against the raw odds. Um, right. The thing is, as Andrew Jaffe points out, virtually zero does not mean zero! The universe is a very big place. If life managed to develop here, then why shouldn't it have developed somewhere else? The chances may be vanishingly small, but there are a lot of planets out there, and we can only see them in our own tiny corner of the Universe. A very small number multiplied by a very big number may still be small, but it's most definitely not zero.
Posted by Megan on Sunday 11th Sep 2005 (11:15 UTC
) | 33 Comments
After spending most of last week helping out with tutorials during this summer school, I only managed to check my email occasionally, and I used a different computer each time. At home I've got used to using the Firefox plugin Sage to catch up on the news and various people's blogs, so last week I actually had to remember urls! Now I have a little script that sits on the server and checks a list of feeds once an hour. It downloads the xml files, parses them using a handy perl module, and writes the results to a webpage. This should make life easier in future. Wow, the power of perl.
Actually, I'm very impressed with the company that host my site. The module I wanted to use was not installed so I emailed technical support to find out if it could be. Within an hour or so they had installed it, and on a Saturday as well!
Posted by Megan on Saturday 10th Sep 2005 (21:13 UTC
) | 4 Comments
At last, after much planning by the scientific organising committee, and a week of hard work, the first European Radio Interferometry School has finished (nothing to do with Eris by the way). Over the last week, thanks to RadioNet, students from all over Europe have attended lectures on calibration of data, spectral line astronomy, high and low frequency radio astronomy (hundreds of gigahertz and tens of megahertz respectively), polarisation, combining data from different arrays of telescopes, error analysis and designing experiments, amongst others. After all that, plus several associated tutorials which I helped out with, the students have hopefully gone away knowing enough to undertake their own radio astronomy observations using any of the many radio interferometers (such as the VLA, PdBI, GMRT, MERLIN, EVN, VLBA) around the world. If you are interested, the lecture notes are all online on the School wiki. It is hoped that these schools will become a regular event, held at a different European institute every two years in antiphase with the IRAM high frequency summer schools.
Even though I was helping out, I have learnt quite a bit from the week myself. For a start I now know what to do with high frequency data, not something that we can do with MERLIN due to the accuracy of the surfaces of our telescopes - to observe at a particular wavelength the surface of your telescope has to be accurate to at least an 8th of a wavelength. This is why mirrors are so shiny, they work at comparatively short wavelengths so they have to be very smooth. To observe at wavelengths of around 1.3 mm for example (a frequency of 230 GHz, routine for the IRAM interferometer), the average variations in the surface accuracy of your telescope must be less than 0.16 mm. MERLIN observes at frequencies much lower than this so our telescopes do not have to be so accurate.
Now the School is over, I plan on sleeping all weekend to recover, although I might find time to catch up on astro-ph and Stuart's reports from this week's AAS meeting in Cambridge.
Posted by Megan on Friday 09th Sep 2005 (21:32 UTC
) | 12 Comments
Fire at the Liverpool Telescope
Yesterday there was a fire on the island of La Palma at the site of the Liverpool Telescope. After the fire which destroyed Mt. Stromlo Observatory in 2003, we were all a bit worried. Luckily, there isn't much vegetation near the telescopes so it hasn't caused too much of a problem. You can check that the telescope is still there on the webcam. There are lots of other telescopes on La Palma, but don't worry, none of them have been damaged either.
Posted by Megan on Thursday 08th Sep 2005 (16:09 UTC
) | 2 Comments
Warning: this post may contain rants.
The last two days have been very long. What with summer school lectures and tutorials all day yesterday, Macc Astro last night, data reduction tutorials today and then taking groups on tours around the observatory, followed by the conference dinner, I'm a bit tired now. To top it all off, coming back from retrieving my bicycle which I left at the physics
department school earlier this afternoon, I was nearly run over by a lunatic in a car who decided to try and run me off the road. I was coming back down a side street near my house when a car coming the other way drove straight at me. I ended up with my tyres touching the curb and I still collided heavily with his wing mirror. I'm still shaking now and I've been home for half an hour. It's not like I was invisible either as I had bright lights on the front and back of my bicycle, and a rather colourful top on. Some people are very, very strange.
Have you ever had one of those dreams where you find yourself in front of a lecture theatre full of people, expecting you to give a lecture on ancient Sanskrit? Today felt like that. We were helping people learn how to reduce data from the PdB interferometer, a high frequency telescope in France, using a package called Gildas. Up until this morning, the software had not worked properly and it was only thanks to hard work on the part of our computer expert, Ant, that we managed to do anything. As none of the tutors had ever got the software to work properly before hand, we were not much use to start with. After a while we worked out most of the problems and could help most people get through the tutorial without too much of a problem.
The afternoon consisted of a trip out to the observatory for all of the summer school students. I was hoping to get a bit of work done, since other people were supposed to be doing the tours. In the end, just as I had sat down with a cup of tea, I was asked to help out as the plan had gone somewhat haywire. In the end, both Dave and I ended up guiding groups around, explaining various things about the observatory and trying to fill as much time as possible. Still, the dinner was nice.
There are just two days left of the summer school now. I plan on staying in bed all day on Saturday.
Posted by Megan on Wednesday 07th Sep 2005 (23:09 UTC
) | 1 Comment
A big thank you to everyone who let me use their images for this month's astronomical round-up: Stuart, Ian Musgrave and Robin Leadbeater, many more were shamelessly stolen from APOD. I also talked about the NGC300 story which gave me a great excuse to play an episode of Slacker Astronomy, that went down well (thanks to Alan for the use of his speakers!). We got a good clear sky for sunset too and, although the trees on the horizon from the car park prevented us from seeing the planets when it got dark enough, we had a good view of the two-day old Moon. :-)
Can I have some sleep now?
Posted by Megan on Tuesday 06th Sep 2005 (22:48 UTC
) | 3 Comments
This week's crazy paper title award goes to...
Things are very strange over on astro-ph. One of the articles on there today is titled "Local Pancake Defeats Axis of Evil". Strange. The paper, submitted as a letter to the Astrophysical Journal, describes a possible explanation for the so-called Axis of Evil effect in the Cosmic Microwave Background (CMB). This is an observed effect where the CMB seems to have some large scale structure which, theoretically, it shouldn't. This paper describes the theory that this structure can be explained by weak lensing caused by large scale structures in the local universe.
Today was the first day of the European Radio Interferometry School (ERIS) in Manchester. I'm helping out with the tutorials and I went along to the lectures this morning as well. When we started the first tutorial we discovered several basic problems with the online notes, so we seemed to spend most of our time running round the two computer rooms sorting out simple problems. Today's tutorials covered calibration and basic imaging using pipeline tools for MERLIN and the EVN. Tomorrow we are doing more on imaging techniques and how to cope with spectral line data. I had better go and read the tutorial notes so have some idea what I'm supposed to be doing!
Posted by Megan on Monday 05th Sep 2005 (22:51 UTC
) | 3 Comments
Close approach of Venus, Jupiter and a two-day old Moon, with Spica not far away CREDIT:
While putting together some images for Tuesday's Macclesfield Astronomical Society workshop I noticed that there is another planetary conjunction this week. After the good weather for last Thursday's conjunction between Venus and Jupiter, we've got our fingers crossed for similar conditions this week.
Around sunset, if you look towards the West you should see a crescent Moon just above the horizon, weather permitting of course. Above and slightly to the left will be Jupiter at a magnitude of -1.6, and further to the left will be Venus at a magnitude of -4 so it will be very easy to spot. As the Sun sets at about 19:50 BST, and our meetings start at 8pm BST, this is perfectly timed for observation from the car park, the only problem might be finding a low enough horizon...
The image on the right shows what the sky will look like at about 19:30 BST, just before sunset here in the UK. The blue grid lines in this image are five degrees apart on the sky to give some idea of the scale.
Posted by Megan on Sunday 04th Sep 2005 (22:02 UTC
) | 8 Comments
Gemini press releases
While looking for images to go with the astronomical events over the last month for the next Macc Astro workshop I ended up on the website of the Gemini Observatory. Amongst their outreach and public information they have quite a collection of press releases. The one I was interested in is the story about NGC 300 from a few weeks back and I found, on page two of the press release, this link to Gemini podcasts. How cool is that?
Posted by Megan on Saturday 03rd Sep 2005 (21:52 UTC
) | 7 Comments
Marzipan (Stuart's blogging program) seems to be working quite well now. The only trouble is, operator error! I've just gone through the database adding an extra field to make the search work after an update, but I was using an old version of the database and managed to completely wipe an entry I made yesterday evening. Grrr.
It wasn't very exciting anyway, just something about my first conference proceedings arriving in the post. It's nice to see your work in a book, even if it does have a very limited readership :-)
Posted by Megan on Saturday 03rd Sep 2005 (06:22 UTC
) | 197 Comments
A light echo around supernova 2003gd
Yesterday there was a paper describing the discovery of a light echo from supernova 2003gd in the nearby galaxy M74. Light echoes are often bizarre looking effects such as the image on the left which shows the light echo from supernova 1987A, an explosion observed by astronomers in the Large Magellanic Cloud (LMC) in 1987. Of course the explosion really happened about 170,000 years ago but the light took that long to reach us due to the distance between the LMC and us.
A light echo forms when the light from the explosion, traveling out in all directions, is reflected by clouds of material (dust and gas) in the interstellar medium (ISM), the "stuff" between the stars. First we see the light from the explosion itself, but later we see the reflected light from these clouds of material around the star which has taken longer to get here because it has travelled further. By measuring the time delay between seeing the explosion and seeing the light echo we can estimate how far from the clouds are from the site of the explosion. The Hubble website has a nice little animation which shows how this effect works. Another famous light echo which you may have seen is that from V838 Mon, a nova which occured in 2002.
So why is 2003gd interesting, and why am I writing about it so early on a Saturday morning?! Well, the answer to the second bit is just that I can't sleep, I've been up for two hours. More importantly, supernova light echoes are rare. This is only the fifth one to ever be detected. They are difficult to find for several reasons. Firstly they are faint, the reflection is much dimmer than the initial explosion, so you need a good telescope and a long observation in order to find them, especially in such distant objects. Most supernova we have seen in recent years (with the exception of 1987A) have occured in galaxies which are several megaparsecs away. You also need a large telescope in order to see enough detail to resolve the light echo. The futher away a supernova is, the smaller the angular size of the echo, so the more resolution you will need in order to see it.
Light echoes allow us to investigate the ISM around the supernova in detail. By watching them carefully we can determine how tenuous the ISM is, what it's made of (by using spectroscopy), and how clumpy it is by the structure we see in the echo. All of this helps the theorists who spend their time modeling stellar evolution. In the case of 2003gd, the observations show that the ISM has a similar density to that in our own Galaxy (one or two particles per cubic centimetre), but is made up of smaller dust grains (less than a quarter of a micron on average). Hopefully, more observations will be carried out using the Hubble Space Telescope over the next few years so that more of the structure can be observed as the light echo moves out from the site of the explosion.
Posted by Megan on Saturday 03rd Sep 2005 (06:06 UTC
) | 8 Comments
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