Is Pluto a Planet?

Is Pluto a planet? You'll probably remember that back in August the issue was debated (MP3 - 10.1MB) at the International Astronomical Union's General Assembly and a working definition of a planet was voted upon making Pluto a dwarf planet. The result left many people - including some planetary scientists - upset and several petitions (here, there and elsewhere) were set up in an attempt to re-instate Pluto to "full" planet-hood.

To many, the result of the vote was a terrible attack on poor little Pluto and they were astonished that anyone could change the number of planets in the solar system. After all, everyone knows that there have always been nine. Don't they? Actually, this isn't true and having an historical perspective on how we have got to the current number is a vital part of the debate. Over the past week I've been reading a great new book titled Is Pluto a Planet? by Professor David A. Weintraub (courtesy of the nice people at Princeton University Press), which gives a very thorough background to the history of the definition of a planet as well as listing and discussing all the possible scientific definitions.

Professor Weintraub starts at the beginning with what the ancients knew of as planets - the Sun, Moon, Mercury, Venus, Mars, Jupiter and Saturn - and how they fitted into the universe. The book then charts the list of planets through the middle ages and into modern times adding and removing a whole suite of objects (comets, asteroids, Ceres, Triton, Planet X and Vulcan to name just a few) as they were discovered, and subsequently found not to be suitable for the label "planet", or in some cases not actually exist! The total number of planets has varied quite a bit with as few as six in 1800 to many as 12 by the 1840s.

Perhaps surprisingly given the title, Pluto doesn't really feature in the book until about half way through, but the first half is necessary to understand why Pluto got onto the planet list in 1930. In fact, I hadn't realised until I read this book that Pluto was actually the fourth planet to hold the title of "the ninth planet", the previous three being Jupiter's moon Europa, the asteroid Pellas and the intra-Mercurial Vulcan.

What the book demonstrates brilliantly is that time and time again philosophers and scientists have had to revise their definitions in light of new objects and new understanding. This constant adjustment is fascinating and really demonstrates how preconceived ideas about how the universe should (or is required to) be are challenged by new discoveries. The first good example in the book is Aristotle who was able to dominate our understanding of planets for over a thousand years until his ideas finally became untenable in the face of all the evidence. This is what science is about and this book shows that many times.

So, does Professor Weintraub answer the question he puts forward in the title? Well, he presents all the scientific arguments for and against and ultimately comes down on one side of the fence (to find out which side you'll have to read the book!). He makes many good points and he certainly made me question many of the planet definitions suggested back in August.

I do have some slight quibbles with the book: I thought that the Galilean moons were introduced a little too early on, I found one of the pictures showing Ursa Major a bit confusing and there was no discussion of the IAU vote in August. It would have been interesting to get Professor Weintraub's view on the IAU vote, but it is understandable that this was omitted as books usually have quite a long lead time before appearing in the shops. Still, these are only minor points and don't detract from the rest of the book which was a good read. If you want a good background to planets and the make-up of our solar system, I would definitely recommend that you read this. You'll probably learn something. I did.

Posted in astro blog by Stuart on Tuesday 31st Oct 2006 (22:35 GMT) | Permalink

Hubble Mission is Go

As reported elsewhere more fully (and on the NASA website) the fifth mission (named SM4) to service the Hubble Space Telescope has been given the green light. This mission will fix the broken gyroscopes which are needed to keep the telescope pointing in the right direction. It will also add new batteries and two new science instruments: Cosmic Origins Spectrograph (COS) and the Wide Field Camera 3 (WFC3).

I'm not sure I completely agree with the official press release's statement that the launch of the HST "marked the most significant advance in astronomy since Galileo's telescope", but it certainly has done great things. It has now been allowed to continue to do so until 2013. Thanks NASA.

Update: Everyone tends to forget that ESA are partners in Hubble so I'll point out that there is a video podcast of the news on ESApod. They get sound bites from David Southwood (ESA Director of Science) and Bob Fosbury (ESA).

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Posted in astro blog by Stuart on Tuesday 31st Oct 2006 (17:28 GMT) | Permalink

Astronomy Media Player

Over the past couple of weeks I've been playing with an idea I had. There are quite a few astronomy podcasts (and video podcasts) around these days and I thought it would be nice if they could be brought together and made searchable.

As a first step towards that aim, I've made a test version of an Astronomy Media Player (AMP) which is partly influenced by things like the BBC's Radio Player. The AMP currently features 20 podcasts and lets you play them within a web browser window using the Flash plugin (for the MP3s) and the Quicktime plugin (for the MP4 video). Each podcast gets its own page and the player will display the latest 20 episodes of each. Appropriate links to the media files and back to the podcast's homepage are also included. Eventually, I would also include a search feature to find content but this is just a test of the basic concept. Try it out:

launch AMP

Is it useful or was it a complete waste of my time? Are there any problems with it? Are there any good astronomy podcasts that I've missed out? Do you have a better name for it than Astronomy Media Player? I would appreciate any feedback good or bad (leave in the comments below), especially about usability.

Posted in astro blog by Stuart on Monday 30th Oct 2006 (19:14 GMT) | Permalink

V838 Mon: the movie

The Hubble Space Telescope (HST) has just released another couple of images in a series of the object V838 Monocerotis. V838 Mon as it is known to its friends is a very strange variable star that underwent a sudden outburst back in 2002. It temporarily became 600,000 times more luminous than our Sun although with it being about 20,000 light years away it didn't outshine the Sun in the sky! What makes this particular outburst quite spectacular is that we can see a light echo; just like a sound echo in a cave, the light is being scattered from clouds of interstellar dust. That means that as time goes on we get to see different parts of the dust clouds illuminated. This makes for a very cool probe of the dust and makes a beautiful series of images as the shell of light expands outwards.

The ESA HST site has an animation fading between the two new images (November 2005 and September 2006) but I decided to make my own movie including all the HST images that now exist. It took a while to rotate and align each image and I then faded between the individual frames and made some MPEG movies. The smaller version should appear below but there is also a larger version. Enjoy!

By the way, the earlier images had much smaller fields of view than the later ones so some stars may suddenly appear but they were there all along.

Posted in astro blog by Stuart on Friday 27th Oct 2006 (20:01 BST) | Permalink

Leafy Moon

Back in September I took a picture of the Moon as it was coming up from behind a house. It has the upper branches of a tree silhouetted against it and I think it turned out quite well.

The Moon on 10th September 2006 CREDIT: Stuart
Pointless trivia: several miles away in the same direction as the Moon, Robbie Williams was performing at Roundhay Park. The concert was very loud as I could make out the tunes.

Posted in astro blog by Stuart on Tuesday 24th Oct 2006 (19:56 BST) | Permalink

See the space station tonight

Since I mentioned viewing the International Space Station last week I've either been plagued by bad weather or it has been too low above the horizon for me to see. However, the weather looks a bit more promising this evening so I'll be outside looking out for it. You may be able to see it from where you live too over the next 10 days or so. Go to Heavens Above and select your country, enter the nearest town and then click on 10 day predictions for the ISS. In general, tonight you will be able to see the ISS towards the south at around 19:25 BST. You will have better viewing (brighter and higher) the further south you are. I'll make things easier by linking to some UK city predictions directly: Birmingham, Cardiff, Dover, Edinburgh, Leeds, London, Manchester, Middlesbrough, Norwich, Nottingham, Oxford, Portsmouth, Stirling.

Posted in astro blog by Stuart on Tuesday 24th Oct 2006 (12:01 BST) | Permalink

Double trouble

Following my post on the damage to telescopes on Hawaii following last Sunday's earthquake, it seems that the Faulkes Telescope Project suffered a double whammy of natural disasters this week. The Faulkes Telescope North (based on Maui, Hawaii) was taken off-line because of the earthquake and the Faulkes Telescope South (based at Siding Spring, Australia) suffered a direct lightning strike on Monday taking it out of action too. This unfortunate timing means that they currently have no functioning telescopes. Faulkes Telescope South should be fixed by early next year and Faulkes Telescope North may forego some planned upgrades in order to provide a working instrument from November onwards.

It has been a bad week for observational astronomy.

Posted in astro blog by Stuart on Friday 20th Oct 2006 (11:27 BST) | Permalink

What is the point of astronomy?

After watching a rather ill-informed CBS opinion piece (via the Bad Astronomer) it made me think about a question that I get asked on a regular basis. "Why do we pay for space science/astronomy?" Strangely, in my experience the question generally comes from men (and occasionally women) of a certain age. I've not answered it here before so I thought I would take a few minutes to give a non-exhaustive list of some of the benefits and space science and astronomy:

  • Satellites (where do I begin?!)
    • Huge advances in weather monitoring and weather prediction have been made possible which has been used by the agriculture industry on a wide scale.
    • Monitoring of global climate by Earth observation satellites which has shown up the problem of global warming.
    • Satellite TV
    • Satellite telephones which allow people in remote places to keep in contact.
    • Disaster monitoring and warnings: think of the advance notice for hurricanes in the US each year, monitoring the spread of forest fires, monitoring crop disease and other forms of remote sensing.
    • GPS that now lets people navigate their way around.
    • GPS has given us tests of General Relativity
    • GPS can be used for weather monitoring (tracking the amount of water vapour) and a network of GPS stations are routinely used by the UK MET Office.
  • Miniturized electronics/microprocessor technology driven by weight reduction considerations for the space programme.
  • WD40 - the famous water dispersant - was developed for the Mercury space programme
  • The pumps used in the portable life support system for the Apollo EVA space suits were used in the design of artificial hearts.
  • Monitoring of the Sun not only tells us about the variation in the Sun's output (which contributes a bit towards warming and heating of the Earth) but knowledge of solar flares heading our way can help protect important infrastructure such as national grids (that keep the electricity flowing to your home and offices) and gives us advance notice of radio interference caused when the high energy particles from the solar flare hit our atmosphere.
  • Optical astronomers demand for better detection of photons of light was a large driver in making CCD technology cheaper and more reliable. CCDs are essential in digital cameras but is also used in things like stereotactic breast biopsy machines used to detect tumour positions.
  • Software created by astronomers to automatically identify stars in images has been adapted to identify cancerous areas in mammograms.
  • Radio receiver technology is partly driven by radio astronomers trying to make lower and lower noise amplifiers/receivers to pick up the faint signals from space. The mobile phone industry has benefited from this.
  • Radio interferometry can be used to precisely identify the positions of telescopes on the Earth and can be used in studies of continental drift, earthquakes.
  • X-ray detector technology and X-ray focussing (needed for X-ray telescopes in space) has improved the technology used in a range of medical imaging devices and in techniques which focus X-rays to destroy cancerous tumours.
  • Simulations of astrophysical objects using magnetohydrodynamic codes (modelling moving particles in a magnetic field) and simulations of plasmas are being used to help harness fusion power.
  • Huge astronomical databases are being used to improve database search software.
  • Astronomers find extreme environments (incredibly dense neutron stars, supermassive black holes etc.) which can test our understanding of the physics (and chemistry) of the Universe.
  • Watching for Earth impacting asteroids may be incredibly useful in the future as plenty of advanced notice would give us time to do something about it.
  • Astronomy and space science produce large numbers of scientists and engineers who go into a whole range of other professions.
  • Oh, and it produces some awe-inspiring images.
That is quite a big list and makes no reference to teflon or velcro! For more information on the benefits of astronomy check out the US National Academy Press which has a good book on the subject.

Posted in astro blog by Stuart on Thursday 19th Oct 2006 (02:05 BST) | Permalink

And the winner is...

Back in August I mentioned that the US's National Radio Astronomy Observatory (NRAO) was having another competition to find nice images made by the radio telescopes and interferometers that they operate. I've just seen (via Universe Today who, incidentally, mistakenly describe it as a photograph which it certainly isn't) that the winners have been announced. The winning image was created by combining data taken by the Greenbank radio telescope, the Very Large Array in New Mexico and the Midcourse Space Experiment satellite. It shows a huge - we're talking 1000 lightyears across - interstellar bubble that was probably created by the wind from a few hot, massive stars. As this is actually radio emission we are observing, the colours are not the true colours but are chosen to give you an idea of the different chemicals in the image. Read the full press release for more. I must admit, my eye was more slightly more taken by the zoo of galaxies that took second place.

NRAO 2nd image contest winner
Interstellar bubble 30,000 light years from Earth measuring 1,100 by 520 light years. Image create with data from Greenbank, VLA and MSE spacecraft. CREDIT: Image courtesy of NRAO/AUI and Jayanne English (U. Manitoba) & Jeroen Stil, supported by Russ Taylor (U. Calgary); NRAO/AUI & MSX

Posted in astro blog by Stuart on Tuesday 17th Oct 2006 (19:06 BST) | Permalink

Hawaiian Earthquake Damage

The earthquakes that hit Hawaii on Sunday have affected many of the telescopes based on the islands. The W. M. Keck Observatory report (seen via Slackerpedia Galactica) no injuries and they are currently trying to get all their instruments and telescope back to full operation. The Canada-France-Hawaii telescope also report no injuries but have had quite a bit of damage: the dome has moved on its track (which stopping it rotating), the Right Ascension encoder has been damaged and their conference room and library have also suffered. Gemini North report some debris on the surface of the primary mirror and the telescope mount has shifted with respect to the azimuthal track but otherwise they seem to be optimistic about returning to normal service soon.

Posted in astro blog by Stuart on Tuesday 17th Oct 2006 (18:45 BST) | Permalink

Beautiful image

One of the great things about astronomy is that it produces pretty pictures. This new image from the Hubble Space Telescope is one of the most beautiful I've seen in a while. It is like a shining, jewel encrusted piece of embroidary. The image shows the central regions (the yellow/orange blobs) of the Antennae galaxies, in the constellation of Corvus, which have been colliding together for around 500 million years.

Antennae Galaxies
HST image of the Antennae galaxies merging together and forming new stars CREDIT: NASA, ESA, and B. Whitmore (Space Telescope Science Institute). Acknowledgement: James Long (ESA/Hubble).
The collision is causing lots of new stars to form (the blue bits) as clouds of hydrogen (the pink bits) and dust (the dark bands) smash into one another. There is so much interesting astrophysics you can do with something like this; from stellar physics to the interstellar medium to galaxy mergers. Fantastic! Anyway, I've got to rush off to give a talk so I'll send you to the press release for the full details and of course the bigger version of the image.

Posted in astro blog by Stuart on Tuesday 17th Oct 2006 (14:00 BST) | Permalink

See the International Space Station

Regular readers to this blog will know that it is possible to see the International Space Station (ISS) from the ground. This can be a really cool thing to see and you can amaze your friends and neighbours by predicting its appearance to within a few seconds.

Unfortunately, during the recent visit of the space shuttle Atlantis, its orbit meant that in the UK we were unable to see it during the evening (although day time passes can produce spectacular sights too). However, over the next few weeks, people in the UK will be able to get prime-time viewing opportunities. According to, we should start to see some visible passes from 20th October. The ISS should appear brighter and higher from 24th October with better viewing the further south you are. If you have never seen the ISS before you should check it out. Find out when and where to look by selecting your location in

Posted in astro blog by Stuart on Monday 16th Oct 2006 (11:20 BST) | Permalink

Galaxy mergers

How do you form a large galaxy? Does it just start out as a big galaxy or do you build it up by colliding and merging little galaxies? Numerical simulations that attempt to model large parts of the Universe seem to show that larger galaxies can be created from the mergers of dwarf galaxies in a "bottom up" approach. Of course they are just simulations, so is there evidence that that is actually happening? The short answer is yes. A nice example is in a new image just released by the Hubble Space Telescope (HST) showing a galaxy undergoing this very process of eating smaller galaxies and putting on the lightyears around its middle.

MRC 1138-262
Composite of separate exposures made by the ACS on the HST. It shows the Spiderweb Galaxy at the centre surrounded by hundreds of other galaxies. CREDIT: NASA, ESA, George Miley and Roderik Overzier (Leiden Observatory, the Netherlands)
The image shows the galaxy MRC 1138-262 - or the Spiderweb Galaxy - sitting in the centre of a large swarm of smaller galaxies, a few of which are being consumed. Of course, as we have come to discover in recent years, the centres of large galaxies tend to be the home of supermassive black holes and the Spiderweb Galaxy seems to be no different. The effects of this central "engine" can be seen by radio telescopes which show huge jets of material being flung out of the galaxy in opposite directions. It seems like a very interesting galaxy but I'm glad I don't live there.

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Posted in astro blog by Stuart on Thursday 12th Oct 2006 (13:31 BST) | Permalink

Critical density

There is something about night time and astronomy that seems to give people an excuse to have pretty random conversations about the big questions. We shouldn't need the excuse but having one is good. Also, if you're like me, you may find yourself trying to work out something crazy such as the average density of the Sun from your own back garden without knowing how far away it is or how much mass it has. I have a thing for crazy numbers.

Recently, someone I know was preparing a talk about dark energy and was trying to think of ways to make the huge/tiny numbers involved in cosmology and particle physics easier for people to understand. This is a common problem in physics because not many people truly comprehend how much, say, 6,000,000,000,000,000,000,000,000 kg actually is (that is about the mass of the Earth in case you were wondering). For this talk the aim was to put the critical density of the Universe in context.

The critical density is the average density that everything - light, matter, dark matter, dark energy and tax returns - would have to be for the Universe to be mathematically 'flat' rather than 'open' or 'closed'. In standard models of the Universe, it turns out that this density is very small indeed. It is equivalent to about 0.000,000,000,000,000,000,000,000,000,01 grams per cubic centimetre; an incredibly tiny number! In slightly more manageable terms, it is equivalent to about 0.01 grams - about the same mass as a grain of sand - spread over the volume of the planet Earth.

Until now, I don't think I had fully realised quite how sparse the Universe really is.

Posted in astro blog by Stuart on Tuesday 10th Oct 2006 (20:20 BST) | Permalink


The trouble with the internet is that websites come and go. Its not easy to know that they will stay in the same place - or even exist - from one year to the next. I don't plan on moving this site anywhere soon, but I do sometimes worry what would happen if, for some reason beyond my control, my site was to disappear. Well it would appear that it will be safe. Rather bizarrely, my blog has been archived by the British Library as part of the UK Web Archiving Project. Quite why they picked my blog over the many thousands of science websites I'm not entirely sure. I assume it is because I'm based in the UK which seems to be the limit of their remit and have a Creative Commons copyright policy. I must say, it is nice to think that the British Library is keeping a copy of everything I write here. However, I now have a horrible feeling of responsibility.

Posted in astro blog by Stuart on Tuesday 10th Oct 2006 (01:04 BST) | Permalink

Hubble finds planets

The Hubble Space Telescope appears to have found 16 extrasolar planets - planets orbiting stars other than the Sun - that are all around 26,000 light years away from the Earth near the centre of our Galaxy. That is a pretty amazing feat and, if they are all confirmed, will add to the ever increasing list of exoplanets which currently stands at 208.

Hubble spots planets
HST view of the Sagittarius Window. The field contains approximately 150,000 stars, down to 30th magnitude. Green circles identify stars orbited by planets CREDIT: NASA, ESA, K. Sahu (STScI) and the SWEEPS science team
The latest slew of planets were found by the Sagittarius Window Eclipsing Extrasolar Planet Search (SWEEPS) in the central bulge of our galaxy. The region of sky covered by SWEEPS has an angular area less than two percent of that of the full Moon and contained 180,000 stars! The planets that were found were not actually directly imaged; they were found by the transit method which spots the slight dip in light from the parent star when a planet passes in front of it. Of course, this method only finds those planets which happen to pass between us and their star which is a very small fraction of the total number that are likely to be out there.

Taking into account the difficulty in detecting planets at that distance and the tiny fraction that can be found using the transit method, the team claim that this supports the hypothesis that the Milky Way contains around 6 billion Jupiter-sized planets. That is about one for every 30 or so stars. I don't know what the uncertainty on that extrapolation is and I wouldn't have thought you could be too confident extrapolating from 16 to 6 billion. I'll have to wait until the results are published in the journal Nature tomorrow to find out what the uncertainty on that figure is. Still, finding 16 planets is good going.

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Posted in astro blog by Stuart on Wednesday 04th Oct 2006 (19:04 BST) | Permalink

COBE scientists share Nobel Prize

Two of the scientists that headed up the team behind the Cosmic Background Explorer (COBE) satellite have been named as the winners of the 2006 Nobel Prize for Physics. The astrophysicists - John Mather (Goddard Space Flight Centre) and George Smoot (Univ California at Berkeley) - both worked on the mission which was the first to confirm the temperature of the cosmic microwave background radiation left over from the big bang. I've previously written about the CMB, and how you can even detect a little of it in your own living room, so I won't repeat myself here.

Their measurements showed that this primordial radiation, which has been cooling since a time around 300,000 years after the big bang, now has a temperature of 2.7 Kelvin or -270.5 Celcius! Not only did COBE detect this very cool temperature, but it was able to detect miniscule changes in that temperature - we're talking about 100,000th of a degree - when looking in different directions. It was a staggering result when it was announced back in the early 1990s. Hey, it still is even though we now have WMAP and in the future we should have Planck which do (or will do) even more accurate measurements of this. COBE was the experiment that lead the way. My congratulations to both the winners and the rest of the COBE team.

As it happens, there is an interview about the Cosmic Microwave Background (MP3 - 10.7MB) including COBE and WMAP on the October edition of the Jodcast (shameless plug).

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Posted in astro blog by Stuart on Tuesday 03rd Oct 2006 (16:40 BST) | Permalink
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