How many planets?

I just had a sudden worry about the major loser in the reclassification of planets; the fantastic resource that is the website. However, it seems that they are not too bothered about it and have already nimbly updated their title. Plus, they even had the foresight to purchase back in 2003 predating the discovery of 2003 UB313 but after the discovery of Quaoar!

Posted in astro blog by Stuart on Wednesday 30th Aug 2006 (19:05 BST) | Permalink

Antarctic Astronomy

Forget extreme ironing, astronomy is done in some pretty extreme places. Antarctica has to be one of the most extreme not just because of the cold but because of the difficulty in getting to, and living in, the coldest continent on the planet. The Jodcast IAU special has an interview with Michael Burton (chair of Special Session 7 at the IAU General Assembly) about the difficulties of Antarctic astronomy, some of the observations being made there and plans for future telescopes.

Oh, and it seems that Michael also helps run Australia's own take on Cafe Scientifique named Science in the Pub. From the accounts I've heard, it sounds like a lot of fun.

Posted in astro blog by Stuart on Wednesday 30th Aug 2006 (18:33 BST) | Permalink

Planets: questions answered

The blogosphere is now filled with complaints about the new definition by people who don't seem to have read the actual proposal and are getting second-hand news reports from reporters who don't properly understand the implications ether. I would like to point out that most of the points that people raise (many of which are pretty good questions) were discussed (and resolved) in the voting session yesterday. I'll try to list a few of the contentious points here along with some answers. Add any other good questions to the comment section.

  • It shouldn't be allowed; we can't change the definition of a planet! Yes we can. Is the Sun a planet? No, but it was until only a few hundred years ago. What about the Moon? Like the Sun it had its planet status removed. There are also a few examples of large asteroids being named planets and subsequently having their planet status removed when we found out how small they were. Ceres (discovered by an Italian) is a good example of that. We have to re-evalute things as we get more information.

  • Why isn't Pluto a planet? Pluto is one of the largest objects that reside is a huge belt of similar icy/rocky objects named the Kuiper belt. As such it hasn't cleared its orbit and would have to be much bigger to do so. And remember, Pluto has less than one percent of the mass of the Earth.

  • Ceres has cleared its neighbourhood so should be a planet rather than a dwarf planet. Ceres is in the asteroid belt and as such is together with untold millions of asteroids which it has little influence over. That does not constitute clearing its orbit

  • Jupiter has not cleared its neighbourhood. This claim goes on the basis that there are two groups of asteroids sharing an orbit with Jupiter. However, these 'trojan' asteroids sit 60 degrees behind and ahead of Jupiter in its orbit at Lagrangian points (L4 and L5 if you are interested) that exist because of Jupiter. This means that they are dominated/controlled by Jupiter so Jupiter is a planet.

  • Pluto crosses Neptune's orbit so doesn't that mean that Neptune hasn't cleared its orbit. Again, Pluto like many other objects is in a 3:2 resonance caused by Neptune so Neptune is dominating them. That makes Neptune a planet and perhaps Pluto is then an object that is dominated by Neptune (another reason not to be a planet).

  • Planets with satellites do not qualify because they haven't cleared their neighbourhood. Again, the planet is the dominant object and controls the satellites (otherwise they would fly off into space and not be satellites!).

  • If a satellite such as Titan was to leave Saturn and take its own orbit around the Sun it wouldn't be accepted as a planet. Firstly, that is incredibly unlikely to happen but if it did, and it was not dominated by another object then yes it would be a planet.

  • What about Sedna, Quaoar etc? They are on the "watch-list" for dwarf planet status. It will depend on what we find out about their shape, size and how much they control their neighbourhood.

  • Under these rules wouldn't Mercury be a dwarf planet? No. Mercury has hydrostatic equilibrium and dominates its neighbourhood so is a planet.

  • Shouldn't a planet have an atmosphere? No. As examples think of. Mercury and the limited atmosphere on Mars. How much atmosphere would be enough?

  • Extrasolar planets are no longer planets. This resolution was only concerned with "Objects in the Solar System" so doesn't declassify them. It was suggested that extrasolar planets would get their own resolution at some point in the future.

  • Planets not orbiting a star are no longer planets. Again, the resolution only covers objects in our Solar System so says nothing about them.

  • Isn't 'demoting' Pluto just international astronomers being spiteful to the only US discovered planet? No and Clyde Tombaugh would not be turning in his grave either. I should explain that politics isn't split in the same way amongst astronomers as it does amongst politicians. Many astronomers know each other and often collaborate on projects with astronomers in different countries. As individual countries only provide limited funds for projects, it is often necessary to make an international collaboration to get together enough funds. In some ways all astronomers are in a common battle against their own national funding councils so tend to be quite friendly towards each other. The 'anti-American' issue is just ridiculous as far as I can see.

  • We now have to wait three years for the group of trans-neptunian objects (TNOs) which are dwarf planets like Pluto to get a name. I'm not sure about this. The name will now be chosen by a committee of astronomers (as the suggested name was voted against) but I'm not sure if the IAU membership have to ratify this.

Posted in astro blog by Stuart on Friday 25th Aug 2006 (11:49 BST) | Permalink

Fortold in the planets?

Amongst all the hoohah of the last week, and today's decision to reclassify Pluto as a dwarf planet, there have been some interesting examples of people jumping to rather pre-emptive conclusions. Incidentally, the removal of the full planet status for Pluto is something that has been suggested for many years ever since it was found to be much smaller than originally expected. But now back to those pre-emptive comments...

First there were the journalists who took the release of the proposal for the definition of planets as solid fact that had already been agreed upon. Hence all the articles telling us that there were now 12 planets. This was jumping the gun on a huge scale and not giving the IAU membership a chance to vote on the matter. An example I noticed only this morning was in the Guardian Science podcast where Alok Jah incorrectly predicted that the original proposal would be carried saying "I'm a journalist, it's my job to know this sort of thing".

If the journalists (not counting Planetary Radio who properly prefaced their discussion with reference to the vote) had known anything about a large bunch of academics it is that it can be difficult to get them to agree with each other. This is doubly difficult when it comes to picking between fairly arbitrary ways to split up bodies in the Solar System (which come in a whole continuum of sizes) into planets and other bodies.

Astronomers don't actually need to worry if something is or isn't a planet. They are the sizes that they are and have the composition that they do and that is what matters, not convenient lingual boxes to put them in. I'll also add that the debate over this nomenclature has led to criticisms by many astronomers of stamp collecting - a terrible putdown - which refers back to the famous (amongst physicists) quote by New Zealander Ernest Rutherford who postulated the atomic nucleus.

The other pre-emptive folks this week have been the astrologers, especially Jonathan Cainer who was quoted in the Telegraph as saying:

"We astrologers have long known and been predicting the announcement of new planets... These changes do not mean that the predictions we have been making have been wrong. But they do mean that in future we will be able to make predictions that we would not previously have been able to make. Every time a new celestial body is found, it signals major technological changes, so Pluto coincided with the splitting of the atom and Neptune with the invention of photography. Pluto is traditionally the planet of all things nuclear and disastrous. I predict we will see a discovery that will almost certainly see nuclear fusion becoming viable within the next 18 months."

So there you go folks, the world's energy problems may become much easier by the end of 2008. Of course, now that Pluto is a dwarf planet and the other objects he alludes to (2003 UB313, 2005 FY9 and 2003 EL61) are potential dwarf planets, his predictive skills may be a bit rusty. You may reasonably expect Mr Cainer to now tell us that the decisions of astronomers don't matter as these bodies are still planets to him (words to that effect are now on his website) but only last week he was saying:

"Imagine you are a doctor. You have several techniques with which to measure the body rhythms of your patients including pulse, blood pressure, heartbeat etc. One day, you get a letter from the world’s most eminent medical experts advising you of another three more important signs to monitor. That’s roughly what’s going on in my world now. Astronomers may not respect astrologers, but astrologers hold astronomers in very high regard. If they say Ceres, Charon and Xena matter, they matter. Those of us who aren’t already working with these celestial bodies will immediately start learning how to interpret their alignments!"

The emphasis is mine but I think it is clear that he only holds astronomers in high regard when they seem to be doing what he wants. Now that they are doing the opposite he doesn't seem so keen to remove objects from his predictions. Sigh.

Will there be any retractions? Probably not. Does it matter that the reporting isn't accurate if it makes a good headline? I suspect that most people don't care and have probably forgotten the stories from last week anyway. Now, if only they could all admit that they were wrong to jump to conclusions just as the IAU have done this week by taking the planet status away from Pluto.

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Posted in astro blog by Stuart on Friday 25th Aug 2006 (01:34 BST) | Permalink

Planet definition outcome

The IAU have live streaming from the General Assembly about the last draft resolution for the definition of planets. Jocelyn Bell Burnell was chairing the debate (which she does well). It has now finished and the results are finally in although there were votes on having revotes and I think everyone was getting a bit tired. Here are the basic results.

  • Pluto is now a dwarf planet and the traditional eight are just plain planets (the term "classical" was voted down).

  • Ceres is a dwarf planet.

  • 2003 UB313 is probably a dwarf planet.

  • A new class of objects has been created of which the first example is Pluto. These objects lay beyond the orbit of Neptune but are dwarf planets. Presumably this includes 2003 UB313.

  • Charon is just a moon because it is not the "dominant" body in its neighbourhood.
However, Resolution 6b was voted against (as was a recount) so the classification for the objects of which Pluto is the first example has no name. The results is that a committee must now be set up to give it a name.

So we have 8 planets. We have several dwarf planets (Pluto, Ceres, 2003 UB313 and perhaps also 2005 FY9 and 2003 EL61). There is a new class of objects - as yet un-named - which include all the dwarf planets that are beyond Neptune ie. all but Ceres. Is that clear now?

Posted in astro blog by Stuart on Thursday 24th Aug 2006 (15:29 BST) | Permalink

Planet definiton last draft

So the last week has been spent by a few astronomers - by no means the majority as they were busy with things that are arguably a lot more interesting such as exciting science - debating the proposed definition of a planet. There have been raised voices and angry sentiments from some, whilst the later meetings were more stricly chaired. The results are that the proposals have been modified (PDF 883kB) from those that the media pre-empted as 'final decisions' last week.

The new proposal for Resolution 5a is:

The IAU therefore resolves that planets and other bodies in our Solar System be defined into three distinct categories in the following way:

(1) A planet[note 1] is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit.
(2) A dwarf planet is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape[note 2], (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite.
(3) All other objects[note 3] orbiting the Sun shall be referred to collectively as “Small Solar System Bodies”.

Note 1: The eight planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
Note 2: An IAU process will be established to assign borderline objects into either dwarf planet and other categories.
Note 3: These currently include most of the Solar System asteroids, most Trans-Neptunian Objects (TNOs), comets, and other small bodies.

There is also a Resolution 5b:

Insert the word “classical” before the word “planet” in Resolution 5A, Section (1), and footnote 1. Thus reading:
(1) A classical planet (the eight classical planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.) is a celestial body . . .

...and a Resolution 6a:

The IAU further resolves:Pluto is a dwarf planet by the above definition and is recognized as the prototype of a new category of trans-Neptunian objects.

...and a Resolution 6b which then adds:

This category is to be called “plutonian objects.”

to the end of Resolution 6a. So, does all that make sense? We now have four parts of resolutions that will be voted on tomorrow afternoon (24th August 2006). The word "pluton" has been replaced with "plutonian objects" as that is not overusing the word and Pluto could be demoted as a planet.

These all go to a vote by astronomers and if you are around you can watch it online from 14:00 CET onwards. But, please remember folks that there is other stuff happening.

Posted in astro blog by Stuart on Wednesday 23rd Aug 2006 (22:55 BST) | Permalink

Trouble at t'IAU

My spy at the IAU (OK Lisa isn't a spy but that sounds much more exciting) has been sitting in on the discussion about the definition of a planet and tells me that there has been a bit of a heated debate.

It turns out that the orbital mechanics people are a bit annoyed that their field is being ignored whilst hydrostatic equilibrium (spherical bodies) has been given a big role in the proposal. Also, the term "pluton" looks likely to be dropped because it overloads the geological use of the term. Instead there are suggestions of "plutino", "plutroid" and "Tombaugh object" amongst others.

The results of the arguments are that the proposal is now in three parts, although what those three parts are I don't know. All this disagreement doesn't make things look good for the vote on Thursday, as a majority is needed to pass the proposal.

I will point out that there are plenty of interesting astronomical issues being discussed during the week other than this.

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Posted in astro blog by Stuart on Tuesday 22nd Aug 2006 (14:24 BST) | Permalink

Wasted light

Excess lighting at night is bad for all of us not just because it stops us seeing the universe (perhaps we will need Universe Awareness) but because it causes a whole lot of other problems too. Astronomer Darren Baskill writing on the BBC news site points out many of the detrimental effects of badly used lighting. These include the contribution to carbon emissions (the UK uses an entire medium-sized coal-fired power station just to pointlessly light up the night sky rather than the ground), the occasional car accident and plane crash due to over-use of lighting, disruption to animal feeding and breeding cycles and increased visual stress for drivers amongst others.

All this could be made much better if people just used appropriate levels of lighting and angled their lights properly. It is that simple and you can reduce your power bill at the same time. A good example that I have noticed over the last few years are the lights on the M62 motorway between Leeds and Manchester. Quite big stretches now have full cutoff luminares which has noticeably reduced glare.

Thanks to Neil for pointing out the BBC article.

Posted in astro blog by Stuart on Saturday 19th Aug 2006 (14:42 BST) | Permalink

Status of planets

So we have a proposal for the definition of a planet (1.3 MB PDF). It has quite a few clauses and doesn't seem to have gone down well with any astronomers that I have heard. On the Jodcast there is an interview with Prof Ian Robson (4.3 MB MP3) who was in a meeting talking about this very subject earlier today at the IAU. Apparently, the astronomers in that discussion weren't too impressed with the proposal either. I'm starting to wonder if this proposal will get passed next Thursday. If it doesn't, will the IAU have to go away and come up with another?

Posted in astro blog by Stuart on Friday 18th Aug 2006 (19:47 BST) | Permalink

Utter chaos

Don't you just hate it when a plan starts to unravel? That is how I felt from last Thursday as our plans for podcasting from the IAU seemed to fall apart. I didn't anticipate suspected terrorist plots causing us problems so the sudden ban on hand-luggage threw a spanner into the works; it meant that laptops and MP3 players either didn't travel or got put in the hold. Add to that the fact that our microphone doesn't work and the result is that we got nothing for the first two days of the IAU and things weren't looking good until next week. However, things are starting to look up. We have an interview arranged for this afternoon, so look out for it on the Jodcast interview feed early this evening. We are also trying to arrange an interview about the status of Pluto/planets as that will be announced tomorrow.

Don't expect me to be putting much on this blog for the next week or so as I'm too busy trying to sort out the chaos that is currently the Jodcast. Oh, and I have another big thing to prepare for.

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Posted in astro blog by Stuart on Wednesday 16th Aug 2006 (11:46 BST) | Permalink

500 posts old

This post is a special one. Not for the content but because I noticed that it is the 500th post I have written and it is roughly three years since I started this blog. That makes me feel quite old in blogging terms.

Back in 2003 there weren't really any other astronomy blogs around and that is the reason I named this place as Astronomy Blog. Actually, it started off as Astro Blog but I quickly added the "nomy" to make the distinction between the astrology blogs that then existed (I'm glad Ian has taken the name since). It seemed like a good, solid name and nobody else was using it.

The start was lonely, but I'm happy to say that since then many other voices have appeared on the scene to give quite a big community of astronomy blogs (see links to right). These cover both hemispheres, many time zones and several continents (although I haven't found any African, South American or Antarctic astronomy bloggers yet). As a result, we have long past the stage where I have the time to keep up with all of them. Perhaps a carnival of the astronomy blogs would be a good idea for the future. Is anyone up for that?

Posted in astro blog by Stuart on Tuesday 15th Aug 2006 (01:10 BST) | Permalink

Is it or isn't it?

Tom Gehrels writing in the second issue of the IAU's snappily titled conference newsletter - Dissertatio cum Nuncio Sidereo III - states the proposal for the definition of planets that has been put forward to the relevant IAU committees. The proposal keeps Pluto as a planet, as was agreed at the IAU GA in Manchester (2000), and adopts 2003 UB313 (or Xena if you must) as a planet because it is intrinsically brighter than Pluto. If accepted, the definition would be that to classify as a planet the body must have an absolute V magnitude greater than -0.76 (the V magnitude of Pluto). Gehrels points out that this is much simpler than using a classification based on sphericity as it can be very difficult to work out how circular these things are at such a great distance. I'm all for simple and I'm quite happy with Pluto remaining a planet. We just have to wait for the decision.

As I mentioned on my previous post, Thomas Marquart is blogging from the IAU now. Check out his blog for reports on the sessions he has been attending.

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Posted in astro blog by Stuart on Monday 14th Aug 2006 (23:34 BST) | Permalink

IAU Blogging & Podding

Over the next two weeks, the International Astronomical Union is having its General Assembly in Prague, Czech Republic. I've just discovered that there is some live IAU GA blogging by Thomas Marquart so go over to his site and check it out. The IAU have put the conference newsletter on the web and some of the talks will be webcast live too. Over at the Jodcast we are hoping to podcast interviews from the conference if airlines and security allow for laptops/MP3 players to leave the UK. Fingers crossed.

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Posted in astro blog by Stuart on Monday 14th Aug 2006 (18:39 BST) | Permalink

Astronomy Movies

Robert Knop of Vanderbilt University has some nice introductory astronomy movies that he has released under a Creative Commons licence. Amongst other things they show the celestial sphere, and the phases of the Moon although the one showing a month on the ecliptic made me feel a bit dizzy. He also has a nice Java applet which demonstrates why spiral arms are not material arms.

Posted in astro blog by Stuart on Sunday 13th Aug 2006 (23:43 BST) | Permalink

Astronomy interviews

I have a request to make of my readers. Who, in the world of astronomy, would you like to hear interviewed about their work and what would you ask them? Alternatively, what project/mission/telescope would you like to hear more about? Please add any suggestions to the comment section below. I may just follow up any interesting suggestions and they could appear on a future episode of the Jodcast.

Posted in astro blog by Stuart on Sunday 13th Aug 2006 (16:13 BST) | Permalink


The star party last night was good fun and I even managed to see a really impressive meteor. Actually, I'm not sure that it was a Perseid as it was not travelling in the correct direction (probably a sporadic) but it was impressive none-the-less - it seemed quite large and bright leaving a bit of an after-image on my retina. Other people did see quite a few more meteors than I did though as I never seem to be looking in the right direction. The Perseid spotting happened during the gap in the clouds that helpfully appeared for the first hour or so of the star party. Later in the evening it disappeared and total cloud cover resumed. It is a pity we didn't have a big switch to turn off the clouds. Still, despite the poor weather forecast, many people did turn up and I think people had a good time.

Posted in astro blog by Stuart on Sunday 13th Aug 2006 (15:15 BST) | Permalink

Perseid Party

At Jodrell Bank Observatory tonight (Saturday), there will be a Perseid Meteor Shower evening from 9pm until midnight. Macclesfield Astronomical Society will be there, Tim O'Brien will be giving a talk and other astronomers will be on hand to answer questions. For information about tickets, contact the Jodrell Bank Visitor Centre.

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Posted in astro blog by Stuart on Saturday 12th Aug 2006 (01:18 CEST) | Permalink

Radio images

Radio astronomers often feel a bit hard done by because it is difficult to make nice pretty pictures. This has mainly been because radio telescopes have never had more than a few 'pixels', so making an image requires a raster scan. To build up an image like this takes a lot of time, so it doesn't really get done. However, when you connect several radio telescopes up as an interferometer, you can build up an image as the Earth rotates.

Last summer the National Radio Astronomy Observatory (NRAO) in the United States launched a competition to find the best images made with data taken using any NRAO instrument. These include the world's largest steerable radio telescope, the Very Large Array (VLA) and the Very Long Baseline Array (VLBA). The contest had 41 entries submitted by 21 different scientists from around the world. The top prize was USD1000 and was won by Aeree Chung of Columbia University (see image below). Although teh winning image looks like a selection of Cadbury's Roses (foil wrapped chocolates for those that don't know) it is actually a cluster of galaxies in the Virgo cluster. They are now seeking submissions for the second year of the competition.

The winning image (20x20 degˆ2 centered at RA=12h32m0.0s, Dec=10d300.0) shows the neutral hydrogen gas (HI, 21cm) distribution of 47 spiral galaxies in the Virgo cluster on the X-ray hot gas background (ROSAT, Bohringer et al. 1994). CREDIT: Image courtesy of NRAO/AUI and Chung et al., Columbia University

Posted in astro blog by Stuart on Thursday 10th Aug 2006 (01:28 BST) | Permalink

Chandra and the Hubble constant

The Chandra X-ray Observatory has released a new estimate of the Hubble constant - very important for working out lots of things about the universe - using measurements of the Sunyaev Zel'dovitch effect. It is quite late at night here so I won't write a full entry on this one. Instead you can read the articles by Phil, Tom, Fraser Cain or the original press release. The peer-reviewed article should be in Astrophysical Journal today (August 10th).

Posted in astro blog by Stuart on Thursday 10th Aug 2006 (00:48 BST) | Permalink

RS Oph results

Back in February, a star named RS Ophiuchi (pronounced "R S off-you-ki") suddenly got brighter. When things like this happen astronomers get interested because by watching it happens they can try to work out the physics of the object.

Stars that brighten and dim are known as nova (a supernova is a very large increase in brightness when a large star explodes at the end of its life) and it turns out that RS Ophiuchi is what is known as a recurrent nova. It has had outbursts recorded in 1898, 1933, 1958, 1967, and 1985 so it was about time for another. The latest outburst has been pretty exciting because technology has moved on in the past 20 years and we can now observe the change in the object with several different types of telescope at the same time; radio, optical, x-ray etc.

Dr Tim O'Brien describes some of the recent observations (15.6 MB) that have been made of RS Opiuchi on the latest issue of the Jodcast. He also has a paper in Nature which can also be read for free on astro-ph.

Posted in astro blog by Stuart on Tuesday 08th Aug 2006 (12:19 CEST) | Permalink

Stardust@Home is go

One thing that Paola (see my previous entry) pointed out to me was that the Stardust@Home project is now operational. They have got their 'virtual microscope' fixed and you can now help to analyse data from the Stardust spacecraft from the comfort of your own house - perhaps while sitting in bed! Run over to the Stardust site and take the test and contribute to real planetary science - it is much more interactive than seti@home. Plus, you get a credit if you find anything new.

I just took the test and am pleased to say that I didn't fluff it; I identified 10 out of 10 correctly so I can now tell an interstellar grain from standard dust on the surface of the aerogel and scratches. Horray! Now all I need to do is improve my ranking...

A certificate for the completion of the Stardust@Home test CREDIT: Planetary Society/Stardust@Home

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Posted in astro blog by Stuart on Monday 07th Aug 2006 (20:25 CEST) | Permalink

Astro Photos

One of the people I've been working with in Italy - Paola Battaglia - is a physicist, instrumental test engineer and also a very talented amateur astronomer. She has shown me some of her astronomical images taken from Colle dell'Agnello (in the mountains away from the lights and humidity of Milano) and they are really beautiful.

On her website (mainly in Italian) you can see some stunning images of M33, M31, the Pleiades, M42, the Milky Way not to mention the 3rd October 2005 eclipse. Many of these images were created by taking several five minute exposures (along with dark frames) using a Canon digital camera. The separate images were aligned and added together (using free software) in a computer to give a really long exposure final image. This is preferable to taking one single long exposure because it is very difficult to keep the telescope tracking the sky over such a long time. The final images are really very good and better than I might have expected from a digital camera compared to a full astronomical CCD. I'm very jealous of the results.

Posted in astro blog by Stuart on Monday 07th Aug 2006 (19:16 CEST) | Permalink
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