15 billion km on the clock

The Voyager 1 spacecraft set off from the Earth in 1977 and has clocked up quite a few miles since. On 16th August it is due to reach a whopping 100 AU - 14,959,787,069 km or 9,295,573,000 miles - from the Sun. Although 15 billion kilometres is peanuts by the standards of our local stars, that is well beyond all the planets in our Solar System and is the furthest that any artificial object from the Earth has ever been.

Voyager 1 is now heading away from the Sun at a speedy 17 km/s (38,250 mph) through the heliosheath and should pass beyond the heliopause - the point where the wind from the Sun is balanced by the wind from other stars which demarks interstellar space - within the next 10 years. The flight controllers expect that Voyager 1 (and Voyager 2) will still keep returning data up until 2020, so hopefully our first interstellar travellers will then be able to send back some interesting information about the heliopause.

For more information check out the Voyager website and listen to a nice JPL podcast (13.3 MB).

Posted in astro blog by Stuart on Monday 31st Jul 2006 (20:01 CEST) | Permalink

Glorious Galaxies

Galaxies - like most other things in astronomy - come in many shapes and sizes. Hubble (the astronomer rather than the telescope) grouped galaxies into three or four main types. Actually, astronomers like to endlessly classify things, so these classes also break into many sub-groups, but basically there are spiral, elliptical, lenticular and irregular galaxies.

The most familiar shape is probably that of the whirlpool and our own galaxy - the Milky Way - is a spiral galaxy with several spiral arms. How exactly these arms were discovered, considering that we are embedded in it so can't look back at it from afar, is a nice piece of detective work and I'll keep it for another post sometime. Spiral arms are interesting places; they are regions where gas and dust gets compressed and new stars form. The centres are exciting too as they are usually very dense and contain a supermassive black hole. Spirals are the poster-galaxies of the universe and they are always pretty whichever way you look at them.

NGC 908
Image of Starburst Galaxy NGC 908 obtained with FORS2 on the Very Large Telescope between 13 and 14 August 2000. CREDIT: ESO
The second class, and perhaps the most boring to look at, are the elliptical galaxies. As with spiral galaxies they consist of hundreds of billions of stars, but they resemble large, diffuse, football-shaped (in both the American football or the soccer sense) collections of stars. They don't tend to get as much coverage as the flashier galaxies that look like pinwheels, whirlpools or sunflowers.

Next are the lenticulars. These look a bit like a strange cross between an elliptical and a spiral galaxy as they have a disc of material but with a huge bulge of stars too. The Sombrero Galaxy is a brilliant example of a lenticular galaxy.

The last class are the irregular galaxies. This group basically covers all the galaxies which don't neatly fall into one of the other three. Two of our neighbours (the Large and Small Magellanic Clouds) are nice examples of irregular galaxies. These odd-shaped, relatively small galaxies are really interesting because they have either undergone or are in the process of being ripped up or smashed together by the tidal effects of the bigger galaxies. In the case of the LMC and the SMC, our galaxy is messing them up although not quite as badly as it has done to our closest satellite galaxy the Sagittarius dwarf galaxy.

The European Southern Observatory recently published a nice image of NGC 1427A (above) which is about 60 million light years away in the direction of the constellation Fornax.

NGC 1427A
Colour composite image of NGC 1427A, based on observations collected with FORS1 (2002/2003). CREDIT: ESO
This galaxy is moving at a heady 600 kilometres per second towards the centre of the Fornax group of galaxies. This high velocity causes the galaxy to get squashed at the front as it hits gas sitting between the galaxies and this encourages new stars to form. Any life developing on planets orbiting those stars would have a very different view to the one we have as they wouldn't have a milky band across the night sky. They would also have to contemplate their galaxy finally being ripped apart and its contents spread into the space between the other galaxies in the cluster. Mind you, we can't be too smug sat here in our pretty large spiral galaxy. After all, we are due for a close gravitational encounter with the Andromeda galaxy in only three billion years. We too could be thrown out.

Posted in astro blog by Stuart on Friday 28th Jul 2006 (10:03 CEST) | Permalink

Pre-launch testing

OK, so I haven't been keeping the blog updated too much recently and that is because I have been kept very busy. In fact I haven't really been able to keep up with much of the news and have hardly had time to read Tom, Ian, Dave or Phil's blogs either. Instead, I've been helping to test some extremely sensitive scientific instruments that will be launched into space in a couple of years time.

It is amazing just how much testing is actually required to make sure everything works as well as it possibly can. Every single component has to be tuned and its response to different inputs carefully measured. There is a strong motivation to know everything you possibly can about the instrument's behaviour because once it is in space you can't really get there to fit a spare part. OK, that was done for the Hubble Space Telescope, but then that is only a few hundred kilometers up. This instrument will be placed 1.5 million kilometres from the Earth; quite a bit beyond human spaceflight (even beyond human spaceflight of the 1970s).

The tests are pretty intensive with many tens of people involved from many different countries. It is a great environment to work in as everyone is pulling together to get everything done. Plus, northern Italy does a pretty good job on the pasta and gelato fronts. Anyway, I should really get back to work and generate some reports for tomorrow.

Posted in astro blog by Stuart on Thursday 27th Jul 2006 (20:08 CEST) | Permalink

Astronaut Reflections

Today's astronomy picture of the day shows a really cool image of the International Space Station, Piers Sellers and the Earth reflected in the visor of Michael Fossum during the recent Discovery mission.

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Posted in astro blog by Stuart on Wednesday 19th Jul 2006 (21:00 CEST) | Permalink

Space Shuttle Landing

The space shuttle is due to land about now. No doubt it will be on NASA TV. I only wish I was able to watch from where I am but alas my internet connection won't allow it.

Posted in astro blog by Stuart on Monday 17th Jul 2006 (15:11 CEST) | Permalink

Venusian Veil and Vortex

ESA's Venus Express spacecraft is now officially in the operational phase of its mission and is starting to produce quite a lot of science output. The craft is basically a clone of Mars Express so has many of the same instruments. Unlike Mars, Venus has a pretty exciting and substantial atmosphere so Venus Express will not be taking amazing 3D images of the surface like Mars Express, but monitoring the clouds, winds, distribution and chemical composition of Venus' thick blanket. That doesn't make it boring though because Venus is throwing up some surprises.

Let me start by giving you a lovely animation showing the approach of Venus Express towards Venus on 22 May. The animation is created from UV images taken by the Venus Monitoring Camera (VMC) as the spacecraft was approaching the northern hemisphere. It starts out at a distance of about 39,100 from the surface and ends at 22,600 kilometres. Beautiful.

UV images taken by the Venus Monitoring Camera (VMC) on board ESA’s Venus Express spacecraft on 22 May 2006. Full resolution animation (2 MB) CREDIT: ESA/MPS, Katlenburg-Lindau, Germany
If you remember the first image to be sent back by Venus Express in May, you will perhaps recall the dark, double-eye vortex seen over the south pole of the planet. Amongst the latest release of images/videos is an animation showing the vortex changing over time (below). Pretty amazing stuff.

Vortex on Venus
An animation of infrared images taken by the Ultraviolet/Visible/Near-Infrared spectrometer (VIRTIS) on board ESA’s Venus Express. It shows a close-up view of the double-eyed vortex at the south pole of Venus. Full resolution image (4.1 MB) CREDIT: ESA/VIRTIS/INAF-IASF/Obs. de Paris-LESIA

Each wavelength of light in the VIRTIS instrument, is able to examine different depths (altitudes) in the atmosphere so it has also been possible to build up a more three dimensional idea of the feature. According to Pierre Drossart, VIRTIS co-Principal Investigator, from the Observatoire de Paris, France

"It is like if we were looking at different structures, rather than a single one. And the new data we have just started gathering and analysing reveal even stronger differences".

There are a whole slew of other exciting results concerning the depth of the atmosphere as observed in stellar occultation measurements, tracking of cloud motions to infer wind speeds and the confirmation that 'UV absorbers' - which absorb almost half of the solar energy received by the planet - exist high in the atmosphere. Head over to the ESA press release to gore yourself on the details and pretty pictures.

Posted in astro blog by Stuart on Thursday 13th Jul 2006 (12:03 CEST) | Permalink

Saturn and Rhea

The Cassini spacecraft is about half way through its mission and just keeps producing spectacular images that don't quite seem real. Astronomy Picture of the Day has a great image showing Saturn's moon Rhea occulting a cresent Saturn. The image is part of a 60 second long animation (5.1 MB) showing Rhea gliding serenly by Saturn.

Rhea and Saturn
Rhea and a cresent Saturn CREDIT: Cassini Imaging Team, SSI, JPL, ESA, NASA

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Posted in astro blog by Stuart on Tuesday 11th Jul 2006 (20:10 CEST) | Permalink

World Cup Moon

Unless you've been living in a cave for the past month you will be aware of the football (soccer) World Cup. I've been working in Italy for the duration of it, watching the ups and downs and seeing the various nationalities either overjoyed or depressed by their team's performance. I'm pretty glad that I was in Italy for the final (Italy vs France) and to see the reaction of a country winning first hand; that isn't going to happen back home for some time yet going by England's performance throughout the competition.

During the second half of the match I managed to take this photo of the full Moon from the window whilst keeping one eye (and both ears) on the game.

The Moon during the World Cup final, taken from northern Italy CREDIT: Stuart

Overjoyed Italian supporters with the Moon in the background CREDIT: Stuart
Of course as soon as the game finished, on nail-biting penalties, the whole of Italy seemed to erupt with the sound of horns and whistles.

Cheers of "Campioni del Mondo!", and other things I couldn't catch, echoed around the city I'm staying in. It was a fantastic atmosphere with everyone so happy and friendly. Everyone from little old ladies, to young men and women, to entire families were out in the streets celebrating the victory over France in the World Cup final.

I took some pictures, but as you might expect fast moving people at night in poor lighting without a tripod is a difficult thing to do. So, my picture shows some rather blurry (but ecstatic) people with a rather blurry Moon in the background.

Congratulations Italy!

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Posted in astro blog by Stuart on Monday 10th Jul 2006 (12:26 CEST) | Permalink

Our Local Stars

I'm my comments I got a pretty nice question from a gentleman named Peter who works at the Museum of Science and Technology in Syracuse, New York. He wanted to know how many stars systems there were within 100 light years of the Earth. Why? Well, the first radio transmissions on Earth have had around 100 years to travel out into the Galaxy, so any potential civilizations living in nearby star systems could have picked us up. Could intelligent shades of purple be listening to Marconi's first messages or watching us take our first steps on our neighbour in space? They might be, but first lets work out how many star systems there are. Peter does a pretty good calculation which goes like this:

A number of web sites list the closest 25 stars which fall within 12 light years of Earth. If star density is equal, I estimate that the sphere of radius of 100 light years would include ~ 14,600 individual star systems, which is a very small % of the number in the Milky Way.

NASA's Ask an Astrophysicist came up with the same answer as Peter back in 1998 using data from the Gliese Catalogue 3rd Edition (1991) to work out the average density of stars and then using that to work out how many stars there might be within a volume of radius 100 lightyears.

I love back-of-the-envelope calculations and this got me thinking. There have been a few projects over the last 20 years which have measured accurate distances for many nearby stars. The first of these which springs to mind is Hipparcos which measured positions for over 118,000 stars. However, the main Hipparcos catalogue only contains measurements for all stars over a certain brightness and that means that it misses stars that are faint and closer than 100 lightyears. Tycho would probably be more complete but the uncertainties on the distance measurements (actually the parallax) in that database can be quite large. NASA Ames produced a database named NStars back in 1998 to collect good quality data on all stars closer than 25pc (81.5 lightyears) as this would be useful for the future Terrestrial Planet Finder mission.

The NStars database contains 2633 stellar objects in 2029 systems. However, the authors think that this only represents about 30% of the true number of stars in that volume because there are a lot of faint stars out there that haven't been measured yet. Scaling up the volume they cover to a radius of 100 lightyears from 81.5 lightyears and using this 'best guess' we get an answer of around 12,500 systems (16,200 stars). Of course this is a bit hand-wavy and has pretty big uncertainties on it, but it is a handy rough guide. Putting it in context, the Milky Way galaxy (the one we live in) contains around 100,000,000,000 stars, so Peter is spot on when he says that 16,000 is a tiny fraction.

Getting back to the issue of other civilizations listening in to us, our radio leakage is actually quite weak and once you factor in those huge distances between stars, the chance of another civilization actually being able to detect anything more than 'noise' is pretty small. After all, with the largest of our radio telescopes you can pick up a signal equivalent to a mobile phone (cell phone) on Mars, but the nearest star other than the Sun is more than 500,000 times further away and the phone would appear around 300 billion times fainter from there! You would be hard-pushed to pick that up.

Of course all this was assuming the transmissions spread out into space in all directions. This is generally the case, but in 1974 there was a deliberate transmission directed at the M13 star cluster. This message was sent by the Arecibo telescope and covered quite a small patch of sky so the number of stars it will have passed so far is much, much less than 16,200. There still remains one question: would aliens appreciate The Simpsons?

Posted in astro blog by Stuart on Saturday 08th Jul 2006 (01:06 BST) | Permalink


I like to stick to astronomy here but I thought I would just take a moment to remember the terrible events that took place in London one year ago. There will be a national two-minute silence at 12 noon BST (11 am GMT).

Posted in astro blog by Stuart on Friday 07th Jul 2006 (10:01 BST) | Permalink

We like the Moon

OK, now for something very silly - and a little weird - that I saw via the comments on Dave P's blog. It is called "We Like the Moon" and is a Flash animation/song about the Moon by some singing furry creatures one of which is playing a guitar whilst the other is sitting on a small floating Moon. Bizarre!

Posted in astro blog by Stuart on Thursday 06th Jul 2006 (09:35 BST) | Permalink

Big astronomy and credit

In recent years, the number of astronomers/engineers working on individual projects has been increasing as things become more difficult and expensive to achieve. With large groups comes the thorny topic of assigning credit (or blame). Particle physicists are used to papers where the author list can go over several pages and astronomy is now starting to head that way. For instance, the first issue of Astrophysical Journal in 1895 saw 31 out of 32 papers with only one author. By 2000 only 15% of papers had a single author and 15% were written by six or more people.

Long lists of authors names are required to attribute credit to those who have put a lot of time and effort into a particular project. But, if you are a starting-out astronomer, having your name buried in amongst tens of others doesn't exactly help your reputation and a reputation is what is required if you want to get your next job. This is one of the topics discussed in a paper titled Large Surveys in Cosmology: The Changing Sociology

that can be found on the pre-print server astro-ph (via Astrophysics Jobs Rumor Mill). The paper arose from discussions amongst astronomers at the University of Cambridge and the experiences of the author in the 2dFGRS project. As well as attribution it talks about the role of PhD students and young Post-Docs in big projects and the use of email and the internet. An interesting read.

Posted in astro blog by Stuart on Monday 03rd Jul 2006 (18:16 CEST) | Permalink

M82 Vodcast

The Spitzer Space Telescope has a new vodcast named Hidden Universe. This is like their exising podcasts except it comes with fancy graphics and you need Quicktime to view it. The latest (well, second) episode features the starburst galaxy M82. That should make Megan happy.

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Posted in astro blog by Stuart on Monday 03rd Jul 2006 (11:10 CEST) | Permalink
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