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Something silly

It's been a strange weekend. The clocks went back one hour last night and, unlike last year when I had to be up and teaching students on the Sunday morning, I remembered. The weather has been rather uncooperative so I haven't seen much of Mars (my telescope is in a cupboard 20 miles away anyway) but I have started fixing all those problems my computer has had for a while. It now has a working DVD drive so this evening I watched The Dish, one of the greatest films ever. The computer has also had a kernel upgrade so that various niggles have been solved. The stock kernels shipped with most distributions always seem to cause problems, this time the machine has not been powering down properly. After building a new kernel it mostly works, there are just a couple of minor issues with a piece of new hardware left to solve.

Back to astronomy tomorrow... or is it? Depends if you believe the Best of the Web's description of Caltech's Cool Cosmos infrared astrology tutorial!

Posted by Megan on Sunday 30th Oct 2005 (23:28 UTC) | Add a comment | Permalink

Successes and failures

Low Earth orbit is an exciting place just now. Today the first satellite built entirely by European students took off from Plesetsk, the first launch from the site since CryoSat earlier in the month. This small satellite is part of the Student Space Exploration and Technology Initiative (SSETI , nothing to do with SETI by the way) which involved a collaboration of students from across Europe designing and building, from scratch, a working satellite with help from experienced engineers at the European Space Agency. The SSETI Express satellite had to pass all the same reviews and checks that any other satellite launched by ESA has to go through and is the first project to be completed, but more are planned for the future.

Russian engineers have also discovered the fault which led to the failure of the Rockot launcher which should have carried CryoSat into orbit. The problem was a failure in the control system in the upper stage of the rocket. A signal which should have shut down the second stage engines was not received, so the engines continued firing until they ran out of fuel. CryoSat overshot the intended orbit and plumetted back into the sea. Now that the failure has been identified it can be fixed and the launcher can continue to be used. The scientists who worked on the mission are calling for funds to enable them to build another CryoSat.

It is also looking good for Venus Express. The engineers have been busy removing the particles of insulation material that caused the initial delay in the launch campaign and ESA are confident that the craft will be launched well before November 24th when the launch window closes.

For the first time in quite a while the sky is looking good. The rain of the last few days has gone, the wind has dropped significantly and we may actually get to use the telescope tonight. Fingers crossed...

Posted by Megan on Thursday 27th Oct 2005 (16:46 UTC) | Add a comment | Permalink

It's alive!

The Lovell telescope at sunset
The Lovell telescope at sunset CREDIT: Megan

After many weeks out of action due to painting, general maintenance and repairs to the structure, the Lovell telescope is now fully operational again. For a while now it has been in the same position, looking North at a fairly high elevation, so that a team of engineers could work on one of the wheel girders that run underneath the main bowl. The girder had developed a crack which needed fixing properly before the telescope could go back into full operation.

Yesterday the telescope moved back to the parked position (pointed straight up at the zenith) so that the engineers could change the receiver, and today it went back into pulsar mode, scanning the southern horizon observing pulsars in the plane of the Galaxy. It is nice to see it working again :-) You can find out where the telescope is pointing at any time by looking at the webcam, the JB Live page, Stuart's pointing display or the PovRay models, all are updated frequently.

Posted by Megan on Tuesday 25th Oct 2005 (22:21 UTC) | Add a comment | Permalink

Venus Express being prepared for launch (again!)

Venus Express being mated with the upper stage of a Soyuz-Fregat launch vehicle
Venus Express being mated with the upper stage of a Soyuz-Fregat launch vehicle CREDIT: ESA

Venus Express, originally due to launch tomorrow, was delayed due to contamination discovered in the upper stage fairing of the Soyuz-Fregat launch vehicle while it was undergoing final integration last Friday. The rocket's upper stage assembly was removed and taken to the upper composite integration facility at the Baikonor cosmodrome where the engineers have inspected the fairing and the spacecraft to assess the extent of the contamination. ESA's press release says that there were particles of the upper stage insulation loose inside the upper stage. This could have caused problems for the spacecraft's optics (amongst other things) so have to be removed before launch. This is being done with tweezers and vacuum cleaners before the craft's electrical systems are tested and the upper stage is reassembled. With any luck, Venus Express should be ready for launch by the end of the week. The launch window will be open until November 24th so there is a bit of spare time. Some missions have very narrow launch windows in order to place the satellite in just the right orbit or on exactly the correct trajectory, this one is quite large so this delay will not mean major changes to the mission.

Posted by Megan on Tuesday 25th Oct 2005 (16:16 UTC) | Add a comment | Permalink

Pulsars in the Gould belt?

The Gould belt is a region of young stars in the local part of the Galaxy. It was discovered by the American astronomer Benjamin Gould who noted a ring of stars passing through Orion, Carina, Crux, Centaurus, Scorpius, Taurus, Perseus, Cassiopeia and Cygnus. Gould realised that the stars traced out a flattened disk (within which the Sun is located) inclined at 20 degrees to the plane of the Galaxy. Many of the visible stars in this region are young, hot stars known as types O and B in the Morgan-Keenan classification system. These kinds of stars are often found in groups called OB associations, a well-known example is the cluster of stars at the centre of the Orion nebula. Detailed studies of nearby OB associations show that they are often part of this disk which is expanding and has motion relative to the rest of the Galaxy. Recent observations of the region have shown the presence of large numbers of x-ray bright, low mass stars whose distribution matches that of the high-mass stars and OB associations.

The Lund map of the Milky Way with the Gould belt superimposed on the top

The Lund map of the Milky Way with the Gould belt superimposed on the top (yellow). CREDIT: Lund Observatory / Megan

One theory says that the Gould belt was triggered by the passage of a density wave associated with a spiral arm, causing gravitational collapse in a pre-existing giant molecular cloud. In a star forming region, large massive stars form. They use up their fuel very quickly and end their lives as supernovae. The explosions send shock waves into the surrounding gas cloud causing further collapse and star formation in a ring around the initial group of stars.

One possible consequence of a supernova explosion is a pulsar, a rotating neutron star with a high magnetic field and jets of radio emission emanating from the poles. Due to the amount of star formation in the Gould belt, it is likely that there have been many supernova in this region resulting in a number of relatively young pulsars. The EGRET catalogue of γ-ray sources contains around forty sources which are in the same direction as the Gould belt but which have no known counterparts, either pulsar or blazar, the two known kinds of γ-ray emitter.

A group of researchers at Jodrell Bank have used the Arecibo radio telescope to search the sky at some of these positions to see if there are young pulsars associated with 19 of the EGRET detections. They found one new pulsar associated (in position) with a γ-ray source, but it doesn't seem energetic enough to be the actual source of the highly energetic γ-rays. In the paper, the researchers find the distance to this pulsar (measured by a technique known as dispersion measure) is 3.5 kiloparsecs, but to be bright enough to have caused the observed γ-ray emission the pulsar would have to be at a distance of only 70 parsecs! They conclude that it is unlikely that this pulsar is associated with the EGRET source.

Why is all this important anyway? An understanding of nearby star formation processes and history will help when looking at other, more distant, regions of star formation such as those in the centre of starburst galaxies. Nearby regions of star formation are easier to observe because our telescopes can see more detail and if we understand them we can make educated guesses as to what is happening in more distant regions. This can help trace the star formation history of the Universe when looking at very distant starburst galaxies seen as they were in the early Universe.

Posted by Megan on Sunday 23rd Oct 2005 (15:26 UTC) | Add a comment | Permalink

International Year of...

This year is the International Year of Physics (in the UK it was re-branded "Einstein Year") and events have been taking place all around the planet to try and bring physics to schools, the wider public, and audiences who may have ignored it in the past. It is also the international year of Microcredit, the international year of Sport and Physical Education, as well as being in the middle of several international decades: Water for Life (2005-2015), Literacy, (2003-2012), Culture of Peace and Non-violence for the Children of the World (2001-2010), Second International Decade for the Eradication of Colonialism (2001-2010), Roll Back Malaria in Developing Countries, Particularly in Africa (2001-2010) and Eradication of Poverty (1997-2006). The UN must be very busy.

Looking further ahead, 2006 will be the international year of "Deserts and Desertification" while 2007 will be the international year of "the ozone layer" (or "planet Earth") although this may be moved to 2008.

That's not all. 2009 will be the.... wait for it..... International Year of Astronomy! Wow. Paragraph three of that document is interesting:

Today astronomy is studied by a small number of researchers. Although there is general interest in astronomy, it is difficult for the general public to gain access to information and knowledge on the subject.

I hope that astronomy is becoming more accessible to the general public already. There are now a range of magazines which contain varying proportions of observational advice and science articles, and "education and public outreach" is now a much more acceptable use of time for professional researchers than it used to be. A lot of this certainly goes on at Jodrell - the schools are on holiday in England next week so there will be Ask an Astronomer sessions in the visitor centre. Still, there is a lot that can be done, and having a year devoted to astronomy will certainly help.

Why 2009? It will mark 400 years since the Italian astronomer Galileo first used a telescope to observe the heavens, and follows on nicely from the year of planet Earth (whichever year it ends up being!). This will not become official until the UN has their General Assembly in Autumn 2006, but it has the backing of several countries (including Italy) and organisations, including the RAS in the UK and the IAU.

Posted by Megan on Wednesday 19th Oct 2005 (22:02 UTC) | Add a comment | Permalink

Maps of Venus

The interior of Venus

The interior of Venus. The layers are: cloud, surface crust, mantle, outer core, inner core. CREDIT: Megan

Part of the ''fun'' of doing research is having to give talks. At Jodrell, students are expected to give one talk each year, but it doesn't have to be about your research. Last year (with help from Stuart) I did a quiz to find out how much astronomy people actually knew. The next one is approaching and I'm looking for a topic again. It would be good to do something daft like last year, but time is an issue. Venus seems quite topical...

There are likely to be a lot of stories about the planet in the near future, what with the launch of ESA's Venus Express just around the corner. While looking for interesting pictures of the planet I found this interactive map at the Adler Planetarium. Lots of fun!

Maps of the surface of Venus are made using radar because the atmosphere is so thick. The clouds which cover the entire surface largely block visible light but let through radio waves. Probes such as Magellan have mapped the surface of the planet in the past by sending radio signals towards the surface and then listening for the reflections. The time taken for the reflection tells you exactly how far away the surface is from the transmitter. The surface is an exciting place with lots of recently created terrain caused by massive geological activity, huge depressions, massive volcanoes and even pancake domes.

Venus Express is designed to reuse instruments designed for the Mars Express and Rosetta missions and will probe the atmosphere of Venus, rather than the surface. In theory, if conditions had been slightly different, the atmosphere of Earth might have ended up like that of Venus and we would not be here. Despite being further from the Sun, Venus has a higher surface temperature than Mercury because of the thick atmosphere full of greenhouse gases. There are extreme weather patterns such as huge areas of hurricane-force winds that travel around the planet in about 96 hours (four Earth days), despite the planet taking 243 Earth days to turn once on its axis (I wonder if Venusians would still complan that there weren't enough hours in the day). Venus Express will explore the atmosphere using spectrometers, radar sounding, magnetometers and analysis of the plasma it detects.

That's my current thought anyway. If you've got any better ideas for a talk, let me know.

Posted by Megan on Sunday 16th Oct 2005 (16:22 UTC) | Add a comment | Permalink

CMB: message from a Creator?

Does the Cosmic Microwave Background (CMB) contain a message from a creator? That was the question posed by S. Hsu and A. Zee on the astro-ph cross-listings yesterday.

Suggestions made in the past include messages imprinted in human DNA or the Grand Canyon, although both of these require intervention at some point by the being leaving the message, and neither are universal (why leave a message just on one planet?). The authors of this paper suggest that, if they had created the universe and wanted to leave a message for any life that developed, they would leave something universal that could be found by any technically developed species, hence the suggestion of looking for messages in the CMB.

The CMB is often described as the echo of the Big Bang. It is the signal which was emitted from the plasma which filled the universe about three hundred thousand years after the Big Bang. At this time, the plasma had a temperature of around 3000 degrees Kelvin. This signal has been redshifted on the way to us and now appears at a temperature of 2.73 K, in the microwave part of the electromagnetic spectrum. It is universal as the signal comes from all parts of the sky: any observer, looking from any part of the universe, would observe the same patterns in the CMB.

The authors suggest that data from future experiments measuring the CMB (such as Planck) should be analysed to look for patterns which may represent a message from a creator (assuming that there was one of course). Nothing may ever be found but, as they point out in their conclusion, "this may be even more fun than SETI".

Posted by Megan on Saturday 15th Oct 2005 (16:36 UTC) | Add a comment | Permalink

News from ESA

The European Space Agency has been busy recently. As well as CryoSat, they have been analysing more data from Deep Impact and preparing another major craft for launch.

A model of the Rosetta space craft. Credit: ESA

Firstly, ESA's Rosetta satellite, which is on it's way to comet 67P/Churyumov-Gerasimenko, observed Deep Impact as the impactor hit comet Tempel 1 earlier this year. Rosetta has an instrument called OSIRIS which consists of two cameras: one narrow-field and one wide-field. Both were used to image Tempel 1 just before and just after the impact using a range of filters to help them pick out the water and dust. The scientists involved in the mission have been analysing the data and have just published their results in the journal Nature (who will not let you read the whole article without paying for it, sorry). They have calculated the amount of water (4.5 million kg) and the cross-section of dust (330 km2) released from the interior of the comet by the impact. From this they conclude that the ratio of mass contained in dust to that in ice is likely to be greater than one, so there is probably more dust than ice in the interior. They suggest that comets should be described more accurately as "icy dirtballs" rather than "dirty snowballs".

Venus Express being prepared for launch
Venus Express being prepared for launch. Credit: ESA

The other spacecraft they have been working on is Venus Express which is due for launch on the 26th October this year. The craft has now been attached ("mated") to the top section of the Fregat launch vehicle whic will carry it on the first stage of the journey. This was a dangerous part of the launch preparations as both the craft and the upper stage rocket had been filled with the highly flammable fuel needed for course alterations in space. As there is no oxygen in space, rockets have to take their own oxidisers. Some rockets use hypergolics, combinations of fuels and oxidisers which are volatile enough that they ignite on contact. The space shuttle uses hypergolics (monomethyl hydrazine and nitrogen tetroxide) in both its orbital maneuvering system and the reaction control thrusters. The next job with Venus Express will be to attach the umbilical which provides power and communcations while the craft is on the ground. Once that is connected, the engineers can power it up and test that all the systems are functioning correctly.

Posted by Megan on Thursday 13th Oct 2005 (19:34 UTC) | Add a comment | Permalink

China's new astronauts

At lunchtime today, my group went for a meal in a local pub. When we arrived, BBC News 24 was on the TV so, while everyone else ordered, I watched the launch of China's second manned space flight. The two men, selected from a group of six only days before the launch, will spend five days in orbit aboard their Shenzhou VI capsule, the design of which is based on the Russian Soyuz craft which have been used on many missions to the International Space Station. Oddly, the Chinal National Space Agency don't have any information on the launch, but you can read about it on the BBC or the Xinhua news websites instead. China have big plans: they are planning to build their own space station and land a man on the Moon in the near future. I wonder if they might manage it before the Americans return there...

Posted by Megan on Wednesday 12th Oct 2005 (23:31 UTC) | Add a comment | Permalink


A while back I mentioned a new show on the BBC about an astronomer at a fictional observatory in the Australian outback. Well, last night saw the first episode, and it was awful. I've never found Rob Brydon that funny anyway, and the sheer amount of bad astronomy in Supernova just makes it even worse. How many holes can you spot: when he arrived, Rob Brydon's character brough a new radium lens which they needed in order to photograph the dark matter around a black hole which they had to look at that night before it went out of range. Argh. What with the zooming-in capabilities of the telescope and the desks in the telescope dome, anyone watching this is going to end up with a very strange idea of how observatories work. At least they have adaptive optics, they'll need it sitting in the middle of the desert at sea level, the seeing has got to be pretty bad. Still, it did provide hours of entertainment as Stuart picked holes in it! ;-)

Posted by Megan on Wednesday 12th Oct 2005 (23:03 UTC) | Add a comment | Permalink

We have the technology...

Duncan Wingham, the chief scientist on the CryoSat mission which failed during launch on Saturday, has said that the spacecraft must be rebuilt. I hope that it is, even though it will take a few years, as it will provide very useful data for climate modelling.

Posted by Megan on Monday 10th Oct 2005 (23:08 UTC) | Add a comment | Permalink

Proper motions in sunspots

After all the excitement of sunspot group 798/808 in September and the recent annular eclipse, the Sun has been pretty exciting in the last month or so. On astro-ph today there was an article, which will appear in a future issue of the Astrophysical Journal, describing high-resolution observations of sunspots. The researchers looked at the cooler penumbral regions with a resolution of about 0.1 arcseconds, watching the motions of the plasma above the surface. They all work for the Instituto de Astrofisica de Canarias, Spain, and on their website they have a collection of movies of these motions. They are all mpegs and are quite large (tens of megabytes), but they are worth the wait.

Solar astronomers already knew there were convective motions in the penumbral regions, but the measured velocities were not high enough to carry away as much heat as they should be doing. These guys used old data taken with a telescope less than one metre in diameter (don't look at the Sun!) equipped with adaptive optics which provided diffraction-limited images. What they found, by watching the movements of filaments within the penumbra, were vertical motions (similar to thse seen in convection cells elsewhere on the Sun's surface) with average velocities of 200 m/s. To carry away enough heat by convection, the velocities would have to be more like 1 km/s, but in the conclusions the researchers point out that the limited resolution of their data may lead to an underestimate of the motions. The mystery is not solved, but now there is more information for the theorists who build models of the Sun to try and work out exactly what is going on.

Posted by Megan on Monday 10th Oct 2005 (23:00 UTC) | Add a comment | Permalink

Children's University

The University of Manchester is keen on interacting with local schools to increase public understanding of science (as well as arts and humanities) and encourage more children to consider higher education as an option, particularly in inner city areas where it is not a "traditional" path.

One thing they have been working on for a while is the Children's University project. They have been putting together a series of web-based activities, starting with astronomy as a test subject, intended for Key Stage 2 (7 to 11 year-olds) and some of the activities are now online. There is going to be an interactive "Ask an Astronomer" section as well where students can ask questions and get a response from a real astronomer at Jodrell Bank.

Posted by Megan on Monday 10th Oct 2005 (17:44 UTC) | Add a comment | Permalink

Facts and guesses

Apparently, according to Katie Melua,

"There are nine million bicycles in Beijing,
That's a fact, It's a thing we can't deny".

Not only that, but

"We are twelve billion light years from the edge,
That's a guess, No-one can ever say it's true"

I doubt anyone has ever counted all the bicycles in Beijing, but we can guess that there might be that many. According to the UN, Beijing has a population of approximately 13.82 million people, so nine million bicycles doesn't sound too crazy. You could argue that there is possibly more evidence to back up the second line than the first. Astronomers have measured the age of the Universe in several different ways and come up with similar answers (13.7 billion light years incidentally), but that doesn't make it a fact. It's not really a guess either, we have quite a bit of proof, but it is still a theory, that's the way science works. It's nice to see light years used as a measure of distance though!

Posted by Megan on Sunday 09th Oct 2005 (09:15 UTC) | Add a comment | Permalink


Today Jodrell Bank hosted a meeting of representatives from the North West Group of Astronomical Societies. About three times a year, reps from astronomical socieites in the north west of England get together to discuss various issues including: the CfDS, FAS matters, and activities of member societies. NWGAS member societies include Manchester, Liverpool, Chester, Altricham & District, Llandrillo, Southport, Salford, and of course, Macclesfield Astronomical Society. Things are pretty healthy in this part of the world with several active societies, many regular lectures and frequent star parties. The demographics across the region just go to show, not all astronomers are male and over the age of fifty!

Posted by Megan on Saturday 08th Oct 2005 (21:38 UTC) | 1 Comment | Permalink

ESA's CryoSat ready for launch

At 17:02 CEST today, ESA will launch their latest satellite, CryoSat. This orbiter is designed to measure variations in the thickness of the polar ice sheets over the 1000-day mission. The aim is to determine exactly what impact global warming is having on the polar regions of the Earth. Due for launch from Plesetsk in Northern Russia, the satellite will go into a highly inclined orbit in order to maximise its coverage of the poles. The main science instrument is the Synthetic Aperture Interferometric Radar Altimeter (SIRAL), a sensor which will measure the extent of the ice sheets. As the coverage on the ESA website says, sensors similar to this have been used before to measure heights of land and water, but this is the first time it has been done with ice.

CryoSat is unusual in that it has virtually no moving parts. This means less risk of failure, but posed interesting technical challenges for the engineers who designed it. Instead of deployable solar panels, CryoSat has rigid panels fixed the the body of the satellite. It also has two antennas, one for command uplinks and telemetry downlinks which works at a wavelength of around 13 cm (S band), and one which is used to transmit the huge volumes of data to the groundstation at Kiruna which operates at around 4 cm (X band).

ESA have an online countdown where you can check the status of the mission during the launch and early orbit phase.  Groovy.

Posted by Megan on Saturday 08th Oct 2005 (16:39 UTC) | Add a comment | Permalink

Another candidate for the craziest paper title

WR124 as seen by the HST
The Wolf-Rayet star WR124 as seen by the HST CREDIT: Yves Grosdidier, Anthony Moffat, Gilles Joncas, Agnes Acker, STScI, and NASA

On astro-ph today there is an article titled Pixie Dust: The Silicate Features in the Diffuse Interstellar Medium. Sounds very odd but, honestly, it describes serious research. The two researchers who wrote the paper (J. Chiar and A. Tielens) have looked at examples of a type of star known as Wolf-Rayet stars and used them to investigate the interstellar medium (ISM).

The image on the left shows an example of a Wolf-Rayet, or WR, star known as WR124 seen by the Hubble Space Telescope. This one is about 15,000 light years away in the constellation of Sagitta.

There are actually three types of WR star, classified by their spectra. The spectra of WN stars are dominated by nitrogen, those of WC are dominated by carbon, and WO are oxygen-dominant. There is an interesting list of lines seen in the different spectral types along with example spectra for each class at the CfA.

The researchers who wrote this paper looked at four WC stars in our Galaxy in the infra-red part of the electromagnetic spectrum using the Infrared Space Observatory (ISO). These particular stars are heavily affected by extinction: there is a lot of stuff (gas and dust) in the interstellar medium between them and us which absorbs light coming from objects in the distance. This extinction is a common problem in astronomy (it is why there appear to be dark bands in the Milky Way) and, if not corrected for accurately, can cause false conclusions. The problem is that the required corrections are not always known that accurately. This is where the "pixie dust" referred to in the title comes from. The corrections applied seem to work, even though they are not perfectly constrained or always well understood.

By carefully analysing the spectra seen when looking at these four stars the researchers have been able to determine some of the chemistry and mineralogy of the ISM and so better describe this "pixie dust". It may sound strange to observe a star when tryig to investigate the dust, but it works. You can think of it like using a lighthouse beam to probe fog, if you know the properties of the lamp then the amount of light you can see tells you how thick the fog is. Similarly, astronomers have models of these kinds of stars which tell them what the spectra should look like. This ideal spectrum can be subtracted from the actual data to leave just the spectrum due to the extinction.

The astronomers who carried out this experiment found that the absorption can be described quite well using a model made up of grains of silicates such as pyroxene and olivine. They have produced extinction curves so that other researchers can make use of them when trying to correct for local dust or dust in the Galactic centre. So the pixie dust is not be so mysterious after all.

Tags: ISM
Posted by Megan on Friday 07th Oct 2005 (22:43 UTC) | Add a comment | Permalink

Mars will (not) appear as big as the full Moon!

This evening I was on the roof of the Physics Department School in Manchester teaching a new pair of fourth year students how to use the telescope in the observatory. Unfortunately, the CCD camera decided it didn't want to work properly so we spent most of the evening looking at various objects through the eyepiece. We looked at Alberio, the double cluster, the Pleiades, M15, M31 and we looked for several other objects but the general orange haze of Manchester stopped us seeing them.

The most impressive sight, though, was Mars. The red planet is nearing close approach again and is getting quite large in the sky. Through the 10-inch Schmidt-Cassegrain telescope we have in the observatory the planet was a large disk with variations in surface detail clearly visible. It's the best view of the planet I've had since August 2003 when Mars had it's last close approach. Back then I helped out at a big star party at Macquarie University. Every Friday they open their observatory to the public and on the night of closest approach they had a big star party. Along with a huge number of members of the public, several astronomers from the AAO came along with their families. This year's approach is not quite as close as that one, but it is not far off. From this part of the world, Mars is rising in the East at about 8pm BST and is reasonably high by 10pm.

You may have come across stories that Mars is going to appear as large as the full Moon, but (as you might imagine) this is complete rubbish. Mars is approximately 6700 kilometres in diameter and the closest it will come to the Earth is 69 million kilometres. From simple high school maths you can work out for yourself just how big Mars will get.  At closest, it will appear 20 arcseconds in diameter. Pretty big, but a lot smaller than the Moon which has an angular diameter of about half a degree.

Tags: Mars
Posted by Megan on Wednesday 05th Oct 2005 (23:40 UTC) | Add a comment | Permalink

Clouded out

Predictably, the weather failed to co-operate today and we had solid cloud cover for the entire duration of the eclipse. Still, it wasn't a disaster. It didn't go as smoothly as I'd hoped, but it was fun. Two local schools, including my old school, brought over groups of pupils and there were a few other visitors along with several members of Macclesfield Astronomical Society who came with telescopes, just in case. Even though we couldn't look through our own telescopes, we were able to watch the event thanks to some kind souls (High Moon and Universidad Complutense de Madrid) who were webcasting the event from sunny Spain where they had perfect clear skies.

Total solar eclipse of August 1999 from Cornwall, UKAnnular solar eclipse of October 2005 from Madrid, SpainPartial solar eclipse of October 2005 from Jodrell Bank, UK
An illustration of the different kinds of solar eclipse. Click on each image to enlarge. Credit:Megan / XEphem

The above images show the differences between types of solar eclipse. The image on the left shows the total eclipse of August 1999 which was visible from Cornwall, UK (or would have been, if it was clear). Here, the Moon is pretty much the same size as the Sun and blocked the light completely, allowing us to see the Sun's corona. The middle image shows the annulr eclipse of today as you would have seen it if you were in Madrid, Spain. The Moon is further away from us than it was in 1999 so it appears smaller and cannot completely cover the Sun's disk, leaving a ring of light which is bright enough to outshine the corona altogether. The image on the right shows what we would have seen at Jodrell Bank if the weather had been better. We were far enough away from the line of totality that, at most, only about 60% of the Sun was covered by the Moon.

After all that excitement (I still haven't got over my cold - it's very hard to take a group on a tour of the observatory when you keep having coughing fits), I am going to go to sleep I think.

Tags: eclipse | Moon
Posted by Megan on Monday 03rd Oct 2005 (18:15 UTC) | 2 Comments | Permalink

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