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Thursday, August 31

Hubble catches an eclipse on Uranus

Image credit: NASA / Hubble

You've probably seen a few pictures of one (or more) of Jupiter's moons crossing the surface of the giant planet. Maybe you've even seen a transit through your telescope. Well the Hubble team have managed to do the same for Uranus. This picture shows Uranus' moon Ariel crossing the face of the planet preceded by the moons shadow. This would be an eclipse as seen from the 'surface' of the planet.

Now there's something you won't see very often!

CAS August Meeting Report

Our August meeting prompted a bit more debate than usual.

Starting with the news section and a debate about the recent definition of a planet from the IAU. After a good half and hour or more of discussion the consensus seemed to be that the IAU had failed to come up with a clear consistent decision. On top of that, they had landed the amateur astronomical community with the difficult job of trying to explain the logic to the general public!

Also discussed was news of some direct evidence for dark matter. Again this prompted some debate, with a certain amount of skepticism for the whole concept from some quarters!

The main topic for the evening was no less than "life in the universe". Robin gave us an excellent talk covering; messages to aliens, the search for extraterrestrial intelligence, and a in dept look at the famous Drake Equation.

Two hours fairly flew by and it was great to have so much discussion.

Thursday, August 24

Pluto loses it's planetary status

The IAU have today voted on a series of revised resolutions. The result of which is that Pluto is no longer classified as a planet.

There are several websites covering this story in detail, so I won't repeat them here. Check out;

BBC News
Cumbrian Sky
Bad Astronomy
Tom's Astronomy Blog

I'm still getting my head around this one. Parts of the definition make sense, and other still leave me a little confused! If I make any more sense of it I'll post something later today.

This is sure to be a big topic of debate at our next CAS meeting on Tuesday 29th August, don't forget.

Wednesday, August 23

NASA names the Crew Exploration Vehicle

Image: NASA - Orion crew vehicle with lander

Back in July NASA named it's next generation launch vehicles, Ares I and V. Now they have announced that the Crew Exploration Vehicle which will sit on top of the Ares I rocket will be called Orion. The full press release is here.

More details on the Orion vehicle here and here.

Tuesday, August 22

Seeing Dark Matter?

Dark matter has been the subject of much debate in recent years. Essentially most cosmologists would have us believe that the universe is comprised of 5% 'ordinary matter', 25% dark matter and 70% dark energy.

Image Credit: NASA

Ordinary matter is essentially everything we know about and can detect; galaxies, stars, gas, planets, electromagnetic radiation etc. Dark matter is essentially the additional mass that's needed to explain the observed movement in galaxies and galaxy clusters using Einstein's theory of gravity (general relativity). But one question has been; "Are we assuming that dark matter exists to compensate for a problem with general relativity?". If we had a modified theory of gravity would the need for dark matter disappear?

Recent evidence obtained using the Chandra space telescope strongly supports the existence of dark matter. This article on the Cosmic Variance blog gives more details, and explains the whole issue better than I could.

Check out Planetary Radio

If you haven't already found this then check out this weeks Planetary Radio. The topic this week is not surprisingly the debate of planetary definition. The special guest is author Dava Sobel, author of the excellent books 'Planets'.

At the end of the programme you'll here the poem "Solar System 2.0" by our friend Stuart Atkinson. It's great to hear Stuart getting some real recognition for his excellent poems, and Dava Sobel is complementary as well.

You can check out the radio show here and more of Stu's poems on The 'Verse.

Monday, August 21

The Planets Debate Goes On . . . .

Tomorrow will see a continuation of the debate over the definition of a planet at the IAU conference in Prague. It looks like everything is not quite as clear cut as reports last week suggested. This report from Astronomy Magazine details a number of counter-proposals which are due to be discussed.

You can watch the debate from the conference live on the conference website here. The debate starts at 11:45 BST.

Following tomorrow's debate there will be a final vote on the proposal on Thursday, the closing day of the conference.

August CAS Meeting

Our August CAS meeting is next Tuesday, 29th August. (Not the 31st August, as printed in some of our programmes). This month we'll have all the latest news on the definition of a planet, as well as the main news items from the summer. Also there may be news of another shuttle launch as the next mission is planned for 27th August.

Our main topic will be 'Life in the Universe', a talk by Robin Leadbeater.

I hope to see as many of you there as possible.

Friday, August 18

CAS Observing Evening

Our programme shows an observing evening this weekend, 19th or 20th August. This will not be going ahead, as we still haven't got an observing site arranged.

I am really keen that we get a site identified for September, as observing is a bit part of what we are about. I know that there are lots of 'beginners' who are keen to start observing and these sessions will be an ideal opportunity to learn from some of our more experienced members.

Watch this space!

Thursday, August 17

Our New Solar System

I'm sure you've heard the news already, unless you've been on another . . erm, planet ! Proposals from the IAU to define the term planet now mean that, if accepted, there would be 12 planets in the solar system.

The basic definition of a planet proposed is this . . . .

"(1) A planet is a celestial body that (a) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape1, and (b) is in orbit around a star, and is neither a star nor a satellite of a planet.2"

You can read the IAU press release, question and answer sheet, and the draft of the Resolution "Definition of a Planet", on the IAU website.

What this means is that if all that's approved next Thursday, there will be 12 planets in our solar system. The new ones being Ceres (the largest asteroid), Charon (Pluto's "moon") and 2003 UB313 (or Xena as she is temporarily known). There are also about another dozen objects which could qualify as planets once it's clear whether they pass the roundness test.

Although this definition seems to be a reasonable compromise which is likely to be adopted there is plenty of comment out there on the proposals. Here's a selection.

Phil Plait's views at Bad Astronomy Blog
Stuarts take on things at Cumbrian Sky
Mike Brown (discoverer of 2003 UB313) view

One of the main concerns is the shear number of potential planets under this system. 12 already, another 12 under consideration. Mike Brown reckons there are already 44 trans-neptunian objects discovered which mean the criteria, bringing the number to 53 ! Scientists seriously talk about there being thousands or even millions of icy Pluto sized bodies out there waiting to be discovered.

But I'm reasonably happy. The IAU was selected a definition which is scientific and does not (for the most part) rely on arbitrary limits of size, mass or location. If we apply this definition and it results in thousands of planets in the solar system, that's because there are thousands of planets. If school children can't remember all of them, so what? We don't expect people to remember all the stars, we don't even name all the stars, just the interesting ones and the ones nearby. (come to think of it, can school children name all nine or our current planets ?).

We'll probably need to further subdivide planets in the future, particularly as we learn more about other planetary systems, just like we have for stars. Again that's no problem.

Things are likely to be confusing for a while, as best summed up in Stuart's brand new poem. But looking on the positive side, this is a great opportunity to get people talking about and interested in astronomy. Just yesterday at least half a dozen people at work asked me about the news and what it meant. We should use the opportunity to promote astronomy. I can see the next public event now, "Come and meet the new solar system" . . . .

Wednesday, August 16

Defining a planet

You may well have heard some recent media coverage on a decision to be made soon on the status of Pluto.

Credit: NASA, ESA, A. Stern (SwRI) and Z. Levay (STScI)

There has been much speculation in recent years on the question "what is a planet?". The recent press coverage stems from the 2006 International Astronomical Union (IAU) meeting in Prague, which takes place this week. The IAU will be debating the issue, and has promised to announce a definitive definition in September. LATE NEWS - Phil Plait at the Bad Astronomy Blog is saying there will be some sort of news later today on Pluto.

It worth remembering that this is not a debate just about Pluto, and whether it is a planet or not. The debate is much wider than that. Any definition has to take account, not only of the many Trans-Neptunian Objects in our own solar system, but also the many other planetary systems we have discovered around other stars, in the last 10 years or so.

So should Pluto be a planet or not ? Well my view is yes. Not for the sentimental reasons some people advocate. I'm really not that bothered whether Pluto survives as a planet or not. Lets face it Pluto has only been know as a planet for 76 years (Halley's comet make one orbit of the sun in that time, and we've known about Halleys comet for hundreds of years). Before Pluto was discovered asteroids like Ceres and Vesta were discovered and considered as planets, until our understanding improved and there were 'demoted' to minor planets.

If you somehow exclude Pluto as a planet you have to do it by some arbitrary limit in either size or orbital distance. If you do that you are basing your system on what you know about our own solar system. For example you might say anything smaller than Mars isn't a planet, or anything bigger than Pluto is. But how does that apply if you discover a body only slightly smaller or bigger than the limit? Or what about a similar sized body around another star? Using orbits as an example if we class anything orbiting further away that Neptune as something other than a planet, how does that relate to other planetary systems. Many of the extrasolar planets we have found orbit their stars in a zone closer than Mercury orbits our sun. Does that mean they shouldn't be planets because they orbit too close ?

The most logical and universally applicable definition I've seen is this one;

"A planet is a body that directly orbits a star, is large enough to be round because of self gravity, and not so large that it triggers nuclear fusion in its interior"

That clears up a lot of the confusion, and applies to any foreseeable planetary system we may discover. Under this scheme Pluto, UB 2003 313 and several other objects in the solar system would be planets.

However, there are still some problems. What do we mean by 'round'? Jupiter is certainly a planet by most people's definition but is not spherical because it bulges significantly at the equator ! Also what does "directly orbits a star" mean? What does a 'star' mean for that matter? What about a 'planet' that orbits a brown dwarf?

Some astronomers have suggested terms like 'Fusor' and 'Planemo' to further refine the definitions.

All of which goes to show that there is no easy answer. Perhaps it's time we abandoned the term planet altogether ! Anyway I'm sure the combined brains of a couple of thousand planetary scientists will come to a sensible conclusion. We just have to wait and see. Hopefully we'll soon know the definitive answer to that seemingly simple question "How many planets are there in the Solar System?".

Thursday, August 10

Perseid Meteor Shower this weekend

Don't forget that this weekend is the Perseid meteor shower, when we expect to see far more 'shooting stars' than on a normal night. This year the moon will be bright, making the sky bright enough to block out some of the meteors, but it's still worth getting out and looking up.

Stuart has lots of information on Cumbrian Sky. Also there is information at the Planetary Society website here and here.