Don't look at the Sun!

Update 5 June 2012: Over the next few hours the planet Venus will transit the Sun. This will be visible from many parts of the Earth. Remember to observe with safe solar filters. You can also view the whole thing online via LCOGT, The Royal Astronomical Society or NASA Edge.

Every time there is a solar eclipse you will find astronomers warning you to never look directly at the Sun. Even more importantly, you should not look at the Sun through a telescope unless you have a professional solar filter that covers the front of the telescope. Why?

The Sun is very bright and by focussing the light onto the back of your eye (the retina) with or without a telescope, you are putting a lot of energy (both optical light and infra-red) onto a tiny area. At some point in your life you may have tried to set paper on fire using a magnifying glass, so just think about that being done to the back of your eye. It isn't nice. Even more scarily is the fact that the retina of your eye does not have pain receptors, so you will not even feel the damage being done. It may not even become apparent until later.

Dont look at the Sun

A grape at the focus of a small telescope while looking at the Sun unprotected. CREDIT: Stuart/Megan

Last year, I decided to try to demonstrate just how dangerous looking at the Sun is. Luckily, I am too sensible to use my own eye for this purpose, so I decided to use a green grape instead. It is round and squishy, so vaguely resembles an eyeball. However, a grape doesn't have its own lens to focus the light onto the back of it ,so I reckon it should fare better than a human eye. Anyway, not knowing exactly what to expect, I used some pliers to hold the grape at the focus. For the first few seconds not a lot appeared to be happening. If it was your eye there in place of the grape, you would be cooking your retina in an irreversible way. Anyway, I was slightly suprised a few seconds later when the sunlight had burnt through the outer layer of the grape and hot grape juice squirted out. It sprayed the eyepiece. I made a rather poor quality movie of this, complete with the sound of sizzling grape. If you click on the image you should be able to see it (WARNING: 2.1MB MOV file). The result is not good.

Not only do you blind yourself, but you may damage the optics of your telescope. So, remember folks, NEVER LOOK DIRECTLY AT THE SUN. If you want to observe the Sun, check out the SOHO website or find someone with a solar telescope. You have been warned.

Posted in astro blog by Stuart on Friday 30th Sep 2005 (11:13 UTC) | Permalink

Annular Eclipse

Back in July I gave advance notice of an eclipse in October. Well, it is getting close, so here is another reminder. The eclipse is this coming Monday and will be visible across most of Europe and Northern Africa. As always, the path of maximum eclipse - the bit where the Moon covers as much of the Sun as it is going to - is quite narrow but crosses through Spain (Madrid 08:56 UT), Algeria (Algiers at 09:05 UT), Tunisia, Libya, Chad, Sudan (10:31 UT), Ethiopia, Kenya and Somalia (11:30 UT). From Manchester, we shall see the Moon covering about 60% of the Sun.

The Jodrell Bank Visitor Centre will be opening their doors early (08:30 BST) to let people watch the eclipse and do various other things. Other observatories across Europe will no doubt be having events too. There are several webcasts planned - hopefully NASA TV get better weather than they did in Greece for the transit of Venus.

Posted in astro blog by Stuart on Wednesday 28th Sep 2005 (22:17 UTC) | Permalink

I'm back

Hello dear reader. For the last few weeks I have been busy thinking hard and writing (or trying to) almost every waking hour of every day including the weekends (the DPS conference was a break!). That is why I have not had much chance to think about posting an entry to Astronomy Blog for the last couple of weeks. All this work has been leading to a huge, brick-wall of a deadline which has now passed. It is great to feel the stress of the last few months melting away. Unfortunately this has been tempered by the bad news that I got on Monday. Such is life.

Anyway, normal(ish) service shall now be resumed.

Posted in astro blog by Stuart on Wednesday 28th Sep 2005 (18:33 UTC) | Permalink

Radio telescopes in the movies

You may have noticed that Astronomy Blog has been very quiet recently. That is because I'm incredibly busy right now with important work which is taking up pretty much all my time. I should be back in about two weeks, but in the mean time here is something I wrote back in August that I hadn't got around to posting…

The other day I was talking about using radio telescopes to search for extra-terrestrial intelligence (as you do) and the person I was talking to said "you mean like in that film with whatstheirname". I instantly knew that they were referring to the film Contact starring Jodie Foster. This wasn't because of my amazing mind-reading abilities, but because it is one of a select bunch of films to feature radio telescopes.

As well as Jodie Foster, Contact also starred the NRAO's Very Large Array in New Mexico and the Arecibo dish in Puerto Rico. The VLA is a radio interferometer that simulates the effect of having a radio telescope up to 36 km in diameter and usually studies distant radio galaxies, quasars and that sort of thing. The 305-m Arecibo dish has been used in the past by the SETI Institute to hunt for signals from E.T. but also spends a large portion of its time looking for pulsars. The Arecibo dish also featured in the James Bond film Golden Eye.

Talking of alien life, Jodrell Bank's Lovell telescope briefly featured in the recent Hitchhiker's Guide to the Galaxy below a Vogon spaceship. Although I know that the film-makers shot a scene with Jodrell Bank astronomers trying to make contact with the Vogons (real astronomers were used as background actors) it does not seem to have even made the 'deleted scenes' section on the DVD. The Lovell telescope has also appeared in the British sci-fi classic Dr Who. In one episode, Tom Baker fell to his death from the telescope and regenerated into Peter Davison.

My favourite film containing a radio telescope is The Dish, set at the Parkes 64-m radio telescope in New South Wales, Australia. The film follows the events surrounding the Apollo 11 landing in 1969 from a distinctly Australian point of view. Although many people might think the film slow, I think it is great. It asks one of the great questions of our time: "What's it doing in the middle of a sheep paddock?"

If you know of any other radio telescopes in the movies, add them to the comments below.

Posted in astro blog by Stuart on Wednesday 21st Sep 2005 (12:22 UTC) | Permalink

Stellarium 0.7.0

I haven't posted much in the last few days as I'm a bit busy, but I had to point out that the latest version of the fantastic Stellarium software is now available. Stellarium is mainly the work of Fabien Chéreau and is a beautiful, free, planetarium program that runs on Windows and Linux (Mac OSX soon). It displays a pretty realistic looking sky and I have taken it outside on a laptop several times to help people find stars and constellations (great artwork by Johan Meuris). It may not be the most accurate planetarium software available, but it is amongst the prettiest and improves all the time.

The new version has loads of cool enhancements, not least of which is the ability to search for objects. Amongst the other improvements: you can drag the sky with the mouse; the slewing speed has been made slower making it look less jerky; you can choose from four pre-set landscapes; there is now also a workaround to stop it using all your CPU time if you have a slower PC or laptop.

It is a 16.4MB download, but it is most definitely worth it.

Posted in astro blog by Stuart on Friday 16th Sep 2005 (01:48 UTC) | Permalink

Aurora Alert - Sep 11

What a time for Lancaster University to upgrade their AuroraWatch software! While their site is down for an upgrade, we have had some of the biggest solar flares since 1976 and right now the planetary k-index is up to 7. What does that mean? It means that it is a great time to go outside and look for the northern (or southern) lights. These are usually visible from very high or very low latitudes (near the poles) but they are visible further south/north when there is more activity. The aurora have already been spotted from Sweden, the US, Canada and Ian is providing real-time information from Australia and Tasmania. Curse the UK weather. As always, if it is dark and cloud-free where you are, get yourself outside to have a look.

Posted in astro blog by Stuart on Sunday 11th Sep 2005 (09:22 UTC) | Permalink


For the latest info about smaller bodies in the solar system, check out Tom's post about asteroid Ceres and Ian's post about asteroid Itokawa.

Posted in astro blog by Stuart on Saturday 10th Sep 2005 (15:53 UTC) | Permalink

What was the point?

In the last few months I have heard more people asking "what is the point of astronomy?" I don't think this is a growing trend; I'm just more aware that people are asking the question. I won't attempt to answer that particular question here, but it made me think of a related question that some people may be asking: "What was the point of the Division for Planetary Science meeting?".

So what was the point? Most obviously we've (I include you the reader) got to hear all the latest scientific results from a whole range of space missions, ground-based observations and simulations. These have been tremendously exciting, especially in this eventful year with so many fantastic results. But, in many ways, a conference isn't just about listening to academic papers and reading press releases. Some of the benefit comes from the ideas that are sparked in the audience and the discussions that flow from the talks, posters, tea/coffee breaks or even at the pub in the evenings.

Conferences, like DPS2005, allow old friends to meet up and new contacts to be made that may never have happened otherwise. For instance, I overheard two postdocs - one from Scandanavia and the other working at NASA - sharing their simulation ideas excitedly in front of a laptop. That excitement about science, and the rush of ideas that come from a new perspective on a problem, is something I think is important. Of course, not all the discussions will lead to anything, but some of them will. That, in my view, is the point.

Stuart was at the Division for Planetary Sciences 2005 meeting in Cambridge, UK.

Posted in astro blog by Stuart on Saturday 10th Sep 2005 (15:20 UTC) | Permalink

The fairies' midwife

As I mentioned in the previous post, Mark Showalter presented some of the latest Hubble Space Telescope (HST) results on Neptune and Uranus in the last talk of the conference. He was last but by no means least. Those who couldn't be bothered to wait until the end missed some interesting new results and he hinted at some interesting announcements in the near future.

He mentioned the discoveries of S/2003 U1 and S/2003 U2 which are new (the second was a rediscovery) moons of Uranus. They have suggested the names Mab and Overdone to the International Astronomical Union (IAU). In case you didn't know, the moons of Uranus are traditionally named after Shakespearian characters e.g. Desdemona, Puck, Rosalind, Juliet etc. Mab was actually Queen Mab, queen of the fairies, and was described by Mercutio (Romeo and Juliet) as being "no bigger than an agate-stone" and "drawn with a team of little atomies". I'm not sure if that is the reason they picked the name.

Uranus, rings and moons
A composite HST image of Neptune showing the rings and moons. CREDIT: NASA, M. Showalter (Stanford University/NASA Ames Research Center), J. Lissauer (NASA Ames Research Center)

Mark finished his talk with an anagram, as Galileo did when he made a discovery and wanted to claim priority over it (claim that he found it first). The anagram was "Space Odyssey 2001/3: Tinting Uranus". It is fairly obvious that the discovery is going to be about S/2003 U1 and you can probably get the word 'Uranian' too, but I haven't yet worked out what the rest of the letters might say. I'm assuming it is in English but it may not be. Any ideas? Otherwise we shall all have to wait for the announcement in an IAU circular.

Posted in astro blog by Stuart on Saturday 10th Sep 2005 (14:53 UTC) | Permalink


The very last talk of yesterday afternoon, and the entire meeting, was given by Mark Showalter. He presented some Hubble Space Telescope (HST) images of Neptune and Uranus. In this post I will stick to Neptune.

Neptune is the eighth planet from the Sun and is surrounded by rings and moons. Although the rings are not as impressive as those of Saturn, they do have some interesting features. When Voyager 2 flew by in 1989, the outermost of the rings was found to contain arcs of material. The <strike>three</strike> four arcs of material are named: Liberté, Egalité, Fraternité and Courage (I guess Courage was found later). The HST has been taking images of Neptune this year and it now looks as though the Courage and Liberté arcs have pretty much gone - they certainly won't be with us much longer. Egalité and Fraternité are still there though, so they are stable over a period of at least 15 years.

They had also hoped to image Neptune's moon Naiad which orbits within the rings. However, it seems to have disappeared as it wasn't seen in any of the data. Has it actually gone or has it some how dimmed? No one is sure so more observations will be needed.

Posted in astro blog by Stuart on Saturday 10th Sep 2005 (14:33 UTC) | Permalink

Lord of the Rings

This morning I've been at talks covering the rings and moons of Saturn. As I said before, the rings are very dynamic places and some parts of them are constantly changing. There are so many interesting features, where do I start? Rings, ringlets, moons, moonlets, wisps, streamers, kinks, the list goes on. First, I had better give you an image showing the rings and moons, so that you have an idea where everything is.

Saturns rings
The rings and moons of Saturn CREDIT: NASA/JPL

The rings are made of lots of very small objects, as I said earlier, and are very well defined with sharp edges and gaps. That is why they get names such as A, B, F etc. One talk, this morning, discussed meteor bombardment on the rings. The idea is that a meteor would hit the ring from above and then throw material out over the ring - a bit like a splash. Computer simulations show that this actually sharpens the edges of the rings, although I'm not sure that I followed the reasoning behind that. Still, one consequence is that the icy-redish material of the rings gets polluted by dark material from the meteor impact and this gives a smooth colour change in the ring, even though it has a sharp physical edge.

Spokes in Saturns rings seen by Voyager CREDIT: NASA
Back in the time of Voyager, mysterious spokes were observed in the rings. These have not been observed by Cassini, so it is thought that they must be some kind of seasonal effect. Perhaps when the rings are aligned with the Sun getting less illumination, there is less charging of the ring by UV light. Nobody is really sure. But wait! Stop the presses! During the questions of one talk, it was revealed that the spokes may have just been seen by Cassini. Apparently, this was discussed over dinner the other other night. I can't wait to see those images.

Having said that the edges of the rings are well defined, I'm now going to slightly contradict myself. They are sharp but in some places they are wavy and there are streamers, channels and brightenings too. Quite a few of the talks have shown simulations of these structures which were created by simulating a moon and hundreds of thousands of small objects in the ring. The moon moves in a slightly elliptical orbit around Saturn, so will appear to move slightly closer and further away from the point of view of the ring. This means that there is a changing tugging by the moon on the particles in the ring and this perturbs the orbits of the ring particles. The result is that every time the moon gets near to the ring, there is a sort of gouging of the ring - a channel - and if the moon gets close enough it can create a trail of material out of the ring towards the moon - a streamer. This effect is seen in both the Encke and Keeler gaps (A ring) and also in the F ring.

The Keeler gap is around 40 km wide and is near the outer edge of the A ring. A moon in this gap going by the name S/2005 S1 was found in May and produces wavy edges (towards and away from the moon rather than out of the plane of the rings) about 5-15 km in extent. These ripples are large near the moon and damp down as you go further away. But they can last up to about 12 degrees around the ring in longitude - that is 27,000 km!

Posted in astro blog by Stuart on Friday 09th Sep 2005 (13:00 UTC) | Permalink

Pronunciation Guide

Do you find that you don't know how to pronounce Ophiuchus? Just how do you say Enceladus? These are problems that I worry over because I usually read names like this long before I hear anyone say them. This often means that I have to re-adjust my pronunciation.

Is Ophiuchus "offi-oo-cas" or "off-u-cas"? What about Enceladus? I say "En-sell-ahh-dus" but it would appear American astronomers say "En-sell-a-dus". A case of I say tomato and you say...

Stuart is at the Division for Planetary Sciences 2005 meeting in Cambridge, UK.

Posted in astro blog by Stuart on Friday 09th Sep 2005 (09:05 UTC) | Permalink

Ring occultation

I'm sat in the first planetary rings session which is discussing the results from the Cassini mission. The only trouble is that the slides have been zooming past at such a rate that it makes it difficult to keep up when note taking.

Marouf presented data on radio occultations - measuring the radio signal from a distant object such as a star, as it passes behind the rings. As you might expect, the strength of the radio signal is reduced when it goes behind the rings as the particles reflect, absorb and scatter the radio waves. By measuring the change in signal, you can get an idea about how much ring material is in the way. If you watch with time, you get to measure different parts of the ring as the background object moves.

Cassini has been observing at three different radio frequencies (about 1 cm, 3.6 cm and 13 cm wavelengths) and each tells you about different sized particles. Basically, if the ring material has a similar size to the wavelength of the radio waves, there is more scattering and you detect less signal. So, comparing the three frequencies tells you about the distribution in sizes of the grains in the rings without the need to go there with a tape measure.

Let me try to summarize what I've just heard about the A, B and C rings. The A ring is full of dynamic structure with lots of millimetre sized particles near the edge. Cassini seems to have measured a different optical depth than Voyager did but I missed the reason why. The B ring is very dense. The C ring has more centimetre sized particles over the ring than A or B. There seems to be different physical structure at each of the three wavelengths in the C ring. That means that the different sized particles are distributed in different places.

Posted in astro blog by Stuart on Friday 09th Sep 2005 (08:58 UTC) | Permalink


The US acronymn EPO, which stands for Education and Public Outreach, sounds much better than the UK equivalent which is the Public Understanding of Science (PUS). Just what were we thinking in the UK?

On Monday and Wednesday I went to a few of the EPO talks and workshop, as that sort of thing interests me. Perhaps you've picked up on that. I've already mentioned the human orrery but I thought I should give a round-up of some of the other things mentioned.

One of the prize lectures on Wednesday was by Rosaly Lopez who works at JPL. She gave a talk encouraging more planetary scientists to get involved with EPO activities and even suggested half a dozen ways to go about doing it. She talked about how she has become a roll-model, in her native country of Venezuela, and how much enjoyment she gets from doing EPO activities, especially in schools. It was a very inspiring talk.

Moving on to an exciting event to put in your calendar if it isn't already. March 29th 2006 will be a total eclipse of the Sun. Although totality will only be visible across a swath of Africa and Turkey, most of Europe and Africa should get a partial eclipse. The event is being called Sun-Earth Day and NASA will be coordinating a worldwide set of observations so that school kids can do some real science. From what I can gather, they will be looking for contributions from amateur groups in as many places as possible. I've passed my email address on to a guy at NASA that is promoting it, so I'll let you all know more when I get the details.

After the EPO workshop I got talking to a member of the local amateur astronomy association in Cambridge. The CAA have around 700 members and do workshops every Wednesday. They also have fun kids sessions on Saturdays with all sorts of games. He tells me that astronomy PhD students in Cambridge have to give short talks to the public and these go down very well. Perhaps this should be encouraged in more places. He was very enthusiastic and we shared lots of ideas. He may even be able to fit me up with a spare telescope he has, as I don't have my own. That would be fantastic!

Stuart is at the Division for Planetary Sciences 2005 meeting in Cambridge, UK.

Posted in astro blog by Stuart on Friday 09th Sep 2005 (07:59 UTC) | Permalink

DPS Bloggers

Now that we've reached the last day, I discover that there is another DPS2005 blogger. Emily Lakdawalla is the science and technology coordinator for the Planetary Society and has a blog about the conference too. Check it out for all the things I've missed.

Posted in astro blog by Stuart on Friday 09th Sep 2005 (07:55 UTC) | Permalink

Deep impact

I went to the Deep Impact invited talk this morning which was really good. By sitting in the path of the oncoming comet the impact had a total energy of 19 GigaJoules. That is an awful lot of kinetic energy!

The approach images taken from the impactor (can someone link it below as I'm short of time) show a little bit of jitter at the start due to course corrections, but the final jitter is due to dust impact. The impactor was hit by three 1-10 mg dust grains within the last 21 seconds and 1 dust grain of up to 100 mg with three seconds to impact. That last one is not thought to be typical of the rest of the comet though. The dust sizes are mostly greater than 10 micrometres and are a mix of rocky dust and ice.

The comet itself is 3 kilometres (+- 0.1) wide and is covered with craters that have a distribution of sizes consistent with impact craters on other objects in the solar system. The comet nucleus has an odd shape and as it tumbles it changes in brightness in a strange way - the "light curve is double peaked" is the technical term for it.

So what happened at impact. The movie shows and incredibly bright and fast flash of ejecta which is likely to be composed of liquid silicate drops (mixed with copper from the impactor) that were ejected by hydrodynamics (liquid flow) rather than just a mechanical process (solid objects). Following this very brief (less than 0.5 seconds) flash, there was a plume of particles smaller than 10 micrometres that was connected to the surface for several hours. A total of about 10 million kilograms was ejected from the comet compared to the impactor which was only 360 kg. The crater formation was gravity controlled which I think means that the material didn't escape from the comet but landed back on the surface. Somebody correct me if I'm wrong. Although the crater has not yet been seen - not from want of trying by the Deep Impact team - the site of impact is known to an accuracy of around 10m and it is thought that the crater will be about 100m in diameter.

I should just add that tomorrow, due to the infinite wisdom of my supervisor, I shall be going to a meeting in Reading. I shall be back in Cambridge for Friday though so check back then.

Finally, Slacker Astronomy are raising money for the Pontchartrain Astronomy Society. They have been affected by Katrina and Aaron suggestions helping them out. Why not make your own deep impact and contribute?

Posted in astro blog by Stuart on Wednesday 07th Sep 2005 (18:27 UTC) | Permalink


I'm currently sat on the floor (hey, I have good reception on the wireless link) typing away and listening to some of the principal investigators on one of the Huygens instruments explain the current state of British cricket to a lady from the US. Apparently Trafalgar Square has already been booked for the celebrations if we win. It would be the first time in over twenty years. They also explained about our four football teams (soccer if you come from the US) and the fact that the UK consists of four countries - this always confuses people from other countries. They saw that I had listened in, so asked me if I understood the explanations!

Stuart is at the Division For Planetary Sciences Meeting 2005 in Cambridge, UK

Posted in astro blog by Stuart on Wednesday 07th Sep 2005 (17:54 UTC) | Permalink

Martian Atmosphere

Some more bits and bobs that I didn't have time to write about yesterday. This time it is the Martian atmosphere. There have been lots of measurements by Mars Global Surveyor (MGS) and Mars Express using many instruments. The MGS had an accelerometer which took readings during the aerobraking phase as the spacecraft was inserted into its proper orbit. Aerobraking involves using the atmosphere to slow down the craft and basically lose some of the speed that it needed to get to Mars in the first place. The accelerometer measures the acceleration (deceleration in this case) and the amount of it tells you the density of the atmosphere. The first two phases of aerobraking on MGS took almost a year and it was possible to measure densities at heights between 110 and 160 km altitude in the atmosphere as it passed through. The Mars Odessy spacecraft did exactly the same thing and was able to measure densities at heights between 95 and 170 km. In fact, the Odessey spacecraft followed the 2001 dust storms.

The MiniTES instrument on board the Mars Rovers has been making its own atmospheric measurements by looking upwards - it can tell us stuff about the atmosphere at heights from 20m to 2km. It has seen an atmospheric boundary layer, some thermal structure in the atmosphere and evidence of aerosols. It also saw a strong inversion layer during the night. As Spirit is currently sitting on top of Husband Hill, they plane to compare the temperature of the air above the ridge with that over the plains. The hope is that they may detect a breeze or wind coming up the slopes of the hill.

ESA's Mars Express has also been making measurements of the atmosphere. The SPICAM instrument observes at ultra-violet (UV) wavelengths of light so, as you may realise if you think about why you wear sun cream, it can detect the presence of ozone (O3). It has found that there is 300 times less ozone in the Martian atmosphere than on Earth. They have also made the first observation of ozone during the Martian night. This is tricky because they rely on reflected sunlight normally and you don't have that at night. Instead they observed a star occultation. So, where is this ozone? Well it varies with season, latitude and longitude but there seem to be two layers; one near the ground and the other at heights of 40-50 km.

What about all that water that is 'discovered' every couple of years. Well, models suggest that the water ice is deposited during the night and then sublimates during the morning. This happens all year round in the northern hemisphere but only during the winter in the southern hemisphere.

Finally, SPICAM has seen plenty of clouds at mesospheric altitudes and even seen clouds as high as 100 km although they probably wouldn't be seen with your eye if you were there. They have been compared to noctilucent clouds on the Earth.

There was much more discussed but that should do for now.

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Posted in astro blog by Stuart on Wednesday 07th Sep 2005 (17:41 UTC) | Permalink

DPS update

Apologies for the rather intermittent nature of the posts while I'm here at the Division for Planetary Sciences meeting in Cambridge (UK). There is no wireless network in the lecture theatres so I only get chance to post things during tea/coffee breaks. I have more I want to write so I'll post it later. Must dash. Clear skies.

Posted in astro blog by Stuart on Wednesday 07th Sep 2005 (14:53 UTC) | Permalink

Human Orrery

A nice idea was demonstrated by Armagh Planetarium at the EPO session on Monday evening. They have recently built a large-scale orrery from stainless steel plates. Each plate represents the position of a terrestrial planet, Saturn, Jupiter and even objects such as Encke at 16 day time intervals. The idea is that, if you get a big group of people, you can mark out the solar system as it is now (to within 16 days) and see how it will change as time goes by. You just get the people to move foward a disc at a time. This lets you work out where the planets would be in the night sky, explore Kepler's Laws and do plenty of other things that I can't remember now. What I do remember is that it looked like fun.

I'll add a link when I can find one.

Posted in astro blog by Stuart on Wednesday 07th Sep 2005 (14:50 UTC) | Permalink

Aurora on Mars?

One talk (or paper as the double-A S call them) described the possible detection of aurora seen on Mars seen by one of the orbiting spacecraft (it may have been MGS or Mars Express - I can't remember which off the top of my head). Mars doesn't really have a magnetic field so aurora are not expected. The detection was tentative as it only lasted about seven seconds. I don't know how convinced the audience were about this though. Don't book your Martian aurora trips any time soon is my advice.

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Posted in astro blog by Stuart on Wednesday 07th Sep 2005 (14:47 UTC) | Permalink

Windy Mars

There was some interesting discussion about dust devils yesterday. Spirit has been seeing more and more of them. The dust devils typically have diameters from 10 - 200 m and move horizontally at a speed of about 1 - 5 metres per second. However their height isn't yet known as the top hasn't been caught in the images and their rotation rate can't be measured on images taken 20 seconds apart. Answers on a postcard if you come up with an idea on how Spirit can work out their rotation rate.

The dust devils seem to peak around Martian noon as you might expect because they get their energy from the Sun. On sol 486, when Spirit was looking north-west, it spotted a dust devil moving the wrong way! By wrong way I mean that it wasn't moving in the same direction as the wind streaks that are visible on the surface. Having said that, recently the wind has been picking up and now that the dust devils are stronger, they do seem to be moving parallel to the wind streaks.

Those winds can be useful too. Spirit landed with 950 Watt hours and this started dropping to dangerously low levels as sand covered the solar panels. Luckily, a strong wind storm cleaned the panels and Spirit now has 950 Watt hours; more power than it had when it landed!

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Posted in astro blog by Stuart on Wednesday 07th Sep 2005 (14:41 UTC) | Permalink

Ringing the changes

If you compare images of the D-ring taken by Voyager and Cassini you should spot a couple of differences. In the last 20 years, one of the rings has moved in by about 200 km. I see that the Scotsman have beaten me to the story although they didn't show the pictures in their online version. Those rings are quite dynamic places. The images come from the fantastic CICLOPS website. Enjoy.

Saturn D-ring
The D Ring on Saturn as seen by Voyager and Cassini. CREDIT: NASA/JPL/Space Science Institute

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Posted in astro blog by Stuart on Wednesday 07th Sep 2005 (10:38 UTC) | Permalink


One of the speakers on Monday described hunting for new moons in the data sent back from the Cassini probe. They said that if looking for birds is called 'birding', then looking for moons should be called 'mooning'.

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Posted in astro blog by Stuart on Wednesday 07th Sep 2005 (07:53 UTC) | Permalink

Martian Volcanism

The BBC's Paul Rincon has an article about volcanism on Mars from this morning's talks. Go check it out. I will have to keep my eye out for name badges to see if I can find out what Paul Rincon actually looks like!

Posted in astro blog by Stuart on Tuesday 06th Sep 2005 (18:16 UTC) | Permalink

Cat Scratches and Tiger Marks

Cat Scratches

Strange features on Titan named cat scratches which were seen by radar observations from the Cassini spacecraft. CREDIT: NASA/JPL

The image above was taken by the Cassini spacecraft and shows a region near the equator on the surface of Titan. It is actually a radar measurement because you can't see through Titan's thick haze with an optical camera. The particular part that I want you to look at are the strange horizontal marks to the left and far right. These have been nick-named "cat scratches" as they look as though they have been made by a rather large feline. They are particularly interesting because if you look at all of them - over the whole moon - they all seem to be aligned in an east-west direction to within about five degrees. What causes them is a bit of a mystery, if you discount moon sized cats. However, it was suggested yesterday that there may be similar features in Antarctica. We were shown a picture of similar(ish) marks taken by radar over Antarctica. These features couldn't be seen by eye on the ground as they weren't physical ridges. They were just different sized grains of snow that had probably been sorted by the wind into a wave pattern. Perhaps the same has happened on Titan?

Enceladus and the UK

A comparison of the UK and Saturn's moon Enceladus CREDIT: Stuart (based on an image presented at DPS2005 in Cambridge)

Now on to Enceladus which has proved to be incredibly interesting in its own right and is giving Titan a run for its money in terms of excitement here. The image to the right is my recreation of the one we saw during one of the talks. It gives a rough size comparison of Enceladus with something a bit more familiar.

Back on 17th February, Cassini made a fly-by of Enceladus getting as close as 1200 km. Measurements of Saturn's magnetic field showed some deviations from what would be expected and the suggestion that Enceladus had an atmosphere was put forward as a possible explanation. To find out more, a second fly-by was organised which went closer. This showed even more strange things happening to the magnetic field, so a third, super-close, fly-by was scheduled.

On 14th July, Cassini got as close as 173 km to the surface - closer than the ISS is to the surface of the Earth. Putting the data from all three fly-bys together suggests that strange things are happening at the south pole of Enceladus. The current idea that is popular here (and it is backed up by measurements on several instruments) is that there is some type of out-gassing near the south pole. What exactly would cause this, nobody is quite sure. However, like Titan, Enceladus also has some strange marks. In this case, they have been called Tiger Marks and are found exclusively near the south pole of the moon. These stripes - dare I call them ridges? - consist, chemically, of ice and organics. Temperature measurements show that they are warmer than the surrounding area by a significant amount. Perhaps there is some kind of ice volcano (cryovolcanism) at work?

Stuart is currently at the Division for Planetary Sciences 2005 Meeting in Cambridge, UK. The meeting is run by the AAS in cooperation with the RAS.

Posted in astro blog by Stuart on Tuesday 06th Sep 2005 (18:08 UTC) | Permalink

Mars Attacked

WOW! That is my reaction to the talks this morning at DPS2005. They were all about Mars. It is currently morning tea/coffee time but I'm still having trouble connecting to the Internet so this will be posted later (lunchtime).

The first talk was an historical introduction to monitoring of dust storms - both local and global - on Mars. The speaker showed a series of drawings taken over the last few hundred years stretching back to drawings by Cassini (I think) in 1666. The speaker even threw in some controversy at the end (deliberately) by suggesting that the last 100 years of observations of Mars show that global dust activity is not related to an increase in the Sun's output. The controversy is in the fact that this may demonstrate that the Sun is not that big a contribution to our own global warming.

The second talk was by Steve Squyres - works with the NASA Mars rovers - and was fantastic. He is a great speaker and I reckon he would do a superb public lecture. Word has it that he has been on tour recently. I'm sure he could make any reluctant tax-payer decide that planetary science is important to fund! Anyway, to the science. He mainly focussed on the Spirit rover, as it has been doing loads of great geology. It has identified about six classes of rock type, which have all been named after the first sample they were discovered on. They show different chemical compositions and different structures. Working out how they formed should tell us a lot about the history of the areas in which the rovers are exploring.

Steve showed us beautiful pictures from the summit of Husband Hill and the journey there on the big screen. We also saw gigantic panoramas from inside Gusev crater taken by Opportunity. Amazing! He even joked that there is so much data that his team haven't got a chance to analyse it all. He pointed out that a lot of this data is now in the archives so others can help out.

Following that was a talk about ESA's Mars Express. The guy giving the presentation had so much to get through that it was a veritible race to the finish. The chairman kept trying to get him to stop but he just kept going. You could tell that he wanted to tell us everything.

Anyway, I'll stop there because I am now going to the next session.

Posted in astro blog by Stuart on Tuesday 06th Sep 2005 (12:56 UTC) | Permalink

Touchdown on Titan

Yesterday I attended all the talks on Cassini and Huygens. There has been masses of interesting science gained from both missions so in the next couple of posts I shall list some of the things I noted down.

I'll assume that you know the history of the Cassini spacecraft. If not, hopefully Tom or Ian can fill in the details. It finally arrived at Saturn, after a seven year journey, late last year and delivered the Huygens lander to Saturn's largest moon Titan. I'll come back to Cassini in another post, but for now let me describe what happened to Huygens....

Huygens entered the atmosphere of Titan at a height of about 1200 km, although the MASI instrument had been taking measurements of the acceleration from 2800 km up. If you know the mass of the lander and its drag coefficient (how much it gets slowed down by different amounts of air), which we do, you can use the acceleration to work out the density of the air you are moving through. So MASI was able to basically work out how much atmosphere there was. The precise nature of the deceleration even gave a hint that there may be some convection in the atmosphere.

There were also measurements of the temperature (the upper atmosphere was warmer than expected), pressure (there is more as you get nearer the surface!) and chemical structure. A lot has been learnt about Titan's atmosphere. For instance, it turns out that there were six inversion layers at 1020,980,800,680,600 and 510 km, and the atmosphere mainly consists of nitrogen (like the Earth), methane, hydrogen and a little argon. Some theories had suggested there could be other noble gases such as krypton or xenon but none were seen.

As with most space missions something did go wrong. It turned out that one of the two transmission channels, onboard Huygens, malfunctioned and there was a worry that data from the doppler wind experiment was lost. Thankfully, there was a backup plan, so radio telescopes from around the world (including Green Bank, Parkes, Mauna Kea and Pie Town) came to the rescue. They were able to effectively recover some of the lost information which tells us about the wind speeds during the rather bumpy descent. It was bumpy; it swung about by up to about 50 degrees at some points and this can be confirmed by matching up images taken with the cameras. The measurements show that although the upper atmosphere moves in the same direction as the planet rotates, the bottom kilometre had a slight wind blowing in the opposite direction.

There was a speed of sound experiment onboard involving a speaker and microphone. As the temperature or pressure changes the speed of sound also changes, so measuring it gives you a handle on those values. As Huygens approached the surface echos of the speaker could be heard reflecting from the ground! This means that it was possible to measure the speed of Huygens very accurately during the final stages of descent.

The first part of Huygens to hit the ground - at a leisurely 5 metres per second - was the penetrometer (part of the Surface Science Package). This was basically a metal pole that stuck out the base of the lander and measured the impact. The plots of the force (in Newtons), against time from impact, show some interesting features. It looks as though it passed through a very soft top layer, possibly hit a thin crust or ice pebble and then pushed into some wet 'sand' below the surface.

Just after landing the Gas Chromatograph Mass Spectrometer (GCMS) detected a sudden increase in methane. It is thought that the 'sand' underneath the lander was probably damp with liquid methane and so the relatively hot lander made it evaporate; this would give the GCMS, with its opening underneath the lander, a whiff of methane and so explain the 30% increase.

So what chemicals are present on the surface? The data show methane, ethane, carbon dioxide, C2H6 (if you know the proper name of that molecule post your answer below?) and argon. Now I think it is frankly amazing what a few chemicals can actually tell you about a planet. The argon possibly indicates some geoplogical activity although that isn't certain; The ratio of different isotopes of carbon suggests that there is no life - certainly not as we know it anyway. The ratio of isotopes of nitrogen even suggests that Titan has lost several times its present atmosphere over its lifetime.

Even though data were only collected for seventy two minutes after touchdown (hey, that is 26 times longer than originally planned for) further measurements were made. Around 100 images were taken on the surface but as the camera couldn't move they all look the same! The tilt detector in the surface science package noted that the lander was at an angle of 10.5 degrees and even tilted a further half a degree during the hour after landing.

(Note: I shamelessly stole the title for this entry from the title of the public lecture last night).

Posted in astro blog by Stuart on Tuesday 06th Sep 2005 (12:30 UTC) | Permalink

Problems and name dropping

I've been having, or rather my computer has been having, issues with connecting to the Internet. Hence the lack of news. Hopefully the world media has been doing a good job of covering the conference. Apparently it made the Sydney Morning Herald!

I've already almost bumped into Chris Lintott - who makes frequent appearances on the Sky At Night these days - as I went around a corner with a cup of tea. He was filming a piece to camera yesterday so I may be unlucky and appear in the background on a future programme. I've also just had Colin Pillinger and colleagues standing in front of me, while I type this, discussing their experiences with TV media people. I won't say what they said. Actually, Colin seems to be walking with crutches, so he may have had an accident or something. Enough of the name dropping least until I post about Mars!

Posted in astro blog by Stuart on Tuesday 06th Sep 2005 (12:16 UTC) | Permalink

DPS 2005

I am currently sat in Cambridge (the one in the UK!) at the Division for Planetary Sciences (DPS) 2005 meeting. I came down to Cambridge yesterday with glorious weather, but we had pretty heavy thunderstorms last night. Not the best weather when you are staying in a tent.

This morning I attended the Cassini/Huygens sessions as did most of the people at the conference it would appear. The main room was jam-packed with people and some were even watching on a screen in the foyer. I shall write more about some of the interesting scientific results when I get chance. Right now I need to finish my sandwitches and rush off to the next session.

Posted in astro blog by Stuart on Monday 05th Sep 2005 (12:54 UTC) | Permalink

Venus and Jupiter

Animation of Jupiter and Venus
Venus and Jupiter seen setting on the western horizon 1 September 2005 CREDIT: Stuart
If you can be bothered to wait for it to download, you should notice that the image above is an animation. It shows the planets Jupiter and Venus (the lower of the two) as they appeared to set behind the trees at around 8.30 pm BST this evening (yesterday evening if you want to be pedantic). This was the view from  about 20 miles south of Manchester where there is much less light pollution. Pop over to the Bad Astronomy blog to see what it looked like from California, or to Astroblog for a view from down under.

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Posted in astro blog by Stuart on Thursday 01st Sep 2005 (23:10 UTC) | Permalink
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