Carter Observatory

At the top of the cable car, near the Victoria University of Wellington, is the Carter Observatory; the "National Observatory of New Zealand". The observatory doesn't do any research these days (although that may change in the near future when they acquire a professional CCD camera and search for asteroids) but it has at least two telescopes that are used by members of the public.

I had a visit to the observatory yesterday to check it out and visit their planetarium. The planetarium is fairly small (or big if you are used to an inflatable one as I am) but you get an excellent tour of the southern sky from the "Star Guides". They also cover quite a lot of good astrophysics from measuring distances to spectroscopy and redshifts. I enjoyed the show because I was able to orientate myself in the southern skies; I'm just about coping with Orion being stood on his head.

16 inch telescope
Carter Observatorys 16 inch Crisp telescope CREDIT: Stuart

The first telescope you see is the Ruth Crisp 16 inch telescope which recently had its mirror realuminised. It is a Cassegrain system and is electronically driven. The dome is also motorised. The other big telescope they have is an old cast iron and brass refracting telescope. It is a very elegant, gravity-driven telescope which was built in the north of England; there are marks on the drive mount that look as if they were set for a different latitude.

Carter Observatory telescope CREDIT: Stuart

Another cool thing is the kids climbing frame outside. It is set to point at the south pole and is also supposed to show the northern and southern limits of the Sun.

Climbing frame
Carter Observatory climbing frame CREDIT: Stuart

Posted in astro blog by Stuart on Friday 27th Jan 2006 (23:49 UTC) | Permalink


On my way to New Zealand I stopped over in LA for a few days to break up the journey. I was actually staying in Pasadena so managed to visit the California Institute of Technology (Caltech). Caltech does a lot of astronomy research and is involved with many observatories and instruments such as Palomar, Keck, OVRO and the Cosmic Background Imager in Chile. They also have some smaller instruments that are used by undergraduate students such as a 14 inch Celestron telescope in a dome on the roof of the Robinson building.

Dome on the roof of the Caltech Robinson building. CREDIT: Stuart

While I was at Caltech a TV crew were filming for the television series Numb3rs. I haven't seen the programme but it would appear to involve a mathematician solving crimes in LA. There was a whole line of catering trucks and vans for the 'stars' lined up on one side of the campus and they were filming one scene in the campus bookshop when I went to get some lunch.

Posted in astro blog by Stuart on Wednesday 25th Jan 2006 (23:36 UTC) | Permalink


Although the title may look like gibberish it is actually the catalogue name of the smallest mass extrasolar planet found to date; it is just 5.5 times the mass of the Earth and orbits its star at a distance 2.6AU. Each orbit lasts roughly 3800 days - much longer than it would be in our solar system - because its parent star is only about a fifth the mass of the Sun.

There are several techniques used for finding planets around other stars. The most obvious is to take an image of one. That is incredibly difficult firstly because the system is likely to be too far away to distinguish the planet and parent star and secondly because the parent star is so much brighter. It can be like looking for a glow worm next to a sport stadium's floodlight. A second technique finds planets by looking for the tiny wobble they impart on their star as the planet completes its orbit. This doppler method is easier to detect if the planet is larger and close to its star. A third method requires the plane of the planet's orbit to be lined up with the Earth; every time the planet passes between us and the star the overall amount of light is reduced. This is called the transit method and should be familiar to you if you saw the transit of Venus back in 2004.

OGLE-2005-BLG-390Lb was found using a totally different method; gravitational microlensing. This method relies on the star and planet passing directly infront of a distant bright object. As the closer star passes in front of a distant star it acts as a gravitational lens and magnifies the light of the further object. If you are monitoring the distant object you can plot a light curve - how the brightness varies with time - and you see a shape that looks a bit like a child's drawing of a mountain (see below). When the lensing star has a planet orbiting it, the planet can also add to this effect as it passes by. The light curve below shows the planet as the little 'blip' on the right-hand side of the 'mountain'. Measuring the size of the blip tells you about the mass of the planet that caused it.

OGLE-05-390L b
The light curve of a planet 5.5 times the mass of the Earth CREDIT: PLANET, OGLE

This is exciting because it allows us to detect much smaller planets than is currently possible with the other techniques. The only trouble is that microlensing events are rare as they rely on a planetary system passing in front of another star. They are also one off events, so follow-up may have to wait for future space-based missions. Still, gravitational microlensing events such as this may find the first Earth-mass planet.

Posted in astro blog by Stuart on Wednesday 25th Jan 2006 (22:37 UTC) | Permalink

3D Star map

Just before I started out on my holiday, one of my friends sent me a link to an artist who makes geometric sculptures. These are inspired by maths and science and are quite striking. I particularly liked the 3D star map sculpture that shows all the stars within 5 parsecs (16.3 lightyears) of the Sun. It was etched within a glass cube using lasers. Neat.

Posted in astro blog by Stuart on Tuesday 24th Jan 2006 (00:04 UTC) | Permalink

The longest sunset

My flight from London Heathrow to LA set off in the late afternoon. As we were heading west at about 530 mph, we were partially compensating for the rotation of the Earth. That meant that it took the Sun quite a while to set; finally dipping below the horizon when we were somewhere near Greenland. At that point I caught sight of a bright light in the East. I assumed it was a planet because it wasn't twinkling, but as I spotted a few more pin-pricks of light nearby I realised that it was actually the bright star Rigel. I then realised that it wasn't really twinkling because I was at something like 36,000ft so a big chunk of turbulent atmosphere was below me.

I had my camera with me and wondered if I could do some astrophotography. It can be a bit tricky to do a long exposure photograph from a plane as it is moving and shaking and it can be difficult to keep the camera steady. I had a few attempts at a 15 second exposure and the best one is below. I don't think it is too bad all things considered.

The constellation Orion taken from the plane whilst over southern Canada CREDIT: Stuart

The really odd thing about travelling west was that the sunset took a long time to happen and the stars almost seemed frozen in the sky. The sunset sky, blending from orange to dark blue, was beautiful and made even more so by the snow covered mountains and frozen rivers of Canada passing by below.

After finding Orion I was able to find another pin-prick of light stunning in its amber glory. It was Mars; another cold world not too far from the one below.

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Posted in astro blog by Stuart on Monday 23rd Jan 2006 (09:12 UTC) | Permalink

Leaving LA

I'm writing this sat in the terminal at LA paying $0.25 per minute so this will be short. I've had a good couple of days at Pasadena/LA and I'll write a bit more about them once I get to New Zealand and can upload some images.

I got a picture of Orion from the plane while on the Canadian/U.S. border which I thought was pretty cool. I've not been able to visit the Griffith or Mt Wilson observatories because one was closed for renovation and the other was closed until April. Shame. I did get to see the original (I think) drawings of the 200 inch telescope drawn by R.W.Porter which are on the walls of the astronomy department at Caltech. They are very cool and it was great to see them in real life.

Until I reach Wellington, clear skies.

Posted in astro blog by Stuart on Saturday 21st Jan 2006 (01:33 UTC) | Permalink

Half a world away

Last year I was very busy, although I did manage to fit in a short ...umm... break at the DPS2005 conference. In fact, I haven't really had a real holiday in a good few years. My contract finished at Christmas and I thought I would take the chance to get a better idea about the size of this here planet Earth. So, I'm off to California (only briefly), New Zealand, Australia and Japan with an 'Around the World' ticket. Why these countries? Mainly because I have relatives in them and the fact that I've never been to them. For practical purposes this means that there will be fewer posts over the next eight weeks. Having said that, I plan to visit at least one observatory and a planetarium while I'm away and I'll be reporting back on those. Plus, I will get to see the amazing southern skies and possibly a comet.

I'll be leaving from London tomorrow afternoon heading for Los Angeles. Last night I suddenly realised that I will be up in the air over North America during the launch of New Horizons - the spacecraft bound for Pluto. It is extremely unlikely that I would see the launch however as long-haul flights tend to follow Great Circles, so I shall probably be over Canada during the launch window. At an altitude of 10 km, the horizon is about 350 km away (not taking into account refraction and extinction) and even allowing for the fact that the rocket is going up, I wouldn't really stand even the slightest chance of seeing it until it was at least 800 km up (if our ground separation was 3,500 km). Plus it will be heading in the opposite direction to me. I won't see it. Shame. Rob might though, so check out his blog.

Until I next find a computer and something astronomical to write about, I leave you in the capable hands of all the excellent astronomy bloggers in the list to the right. Clear Skies.

Posted in astro blog by Stuart on Monday 16th Jan 2006 (19:52 UTC) | Permalink

Density Waves

When you see a nice spiral galaxy it is tempting to think of the spirals arms as fixed collections of stars, gas and dust that orbit the centre of the galaxy as a solid rather as if you had drawn them onto a frisbee. However, this isn't the case.

The Whirlpool Galaxy (M51) taken with the HST's ACS. CREDIT: NASA, ESA, and G. Bacon (STScI)
If you measure the velocity of the gas, or dust, or stars you find that the velocity remains pretty much the same for stars nearer the centre as those nearer the edge of the galaxy (this isn't true for those in the middle but I'll ignore those). So if they are moving at the same speed doesn't that mean that they all go around together? Well, no and it is all to do with circles. Everything would stay together if it was going in a straight line, but in a spiral galaxy it is going in circles around the nucleus; the stuff near the middle will complete an orbit quicker than stuff further out because it has much further to travel.

If you start off with a bar of stars (or gas, or dust) sticking out from the centre of a galaxy, pretty quickly it will twist itself up so much that you can't really see the arms. By quick I mean a few orbits around the galaxy. This is considerably less than the lifetime of a galaxy, so for us to see spiral arms there must be more to it.

It turns out that the spiral arms we see are not actually solid groups of stars as you might draw on a disc. Instead they simply represent areas where there are more stars, gas and dust (sort of obvious if you think about it). So what is the difference? The individual stars (and clouds of gas and dust) move through these over-dense areas (the spiral arms) while orbiting the centre of the galaxy.

This can be a difficult concept to get your head around, but I saw a good example of it a few weeks ago. On a long stretch of very busy motorway somebody is bound to apply their brakes for one reason or another. If there is a lot of traffic, the car behind will also have to brake a bit and the car behind that one will too and so on. As well as slowing the traffic down, this reduces the space between cars and can result in a traffic jam. Now if you were to watch a long stretch of motorway from a distance you would see that the place where the jam was had more cars in it than a similar-sized patch of motorway where the traffic was flowing freely. Although the passengers may feel that they aren't getting anywhere, the cars are moving through the over-dense region. In fact, the location of the dense region (jam) may even move backwards up the motorway resulting in phantom jams - jams that you come out of wondering why it was there. From a distance you see the dense patch slowly moving backwards while the cars are moving forwards. Now replace the traffic jam with 'spiral arm' and the cars with stars and you'll not think that density waves are so odd.

So, density waves can move around the galaxy much more slowly than the stars/gas/dust and can last for quite a few orbits. This helps solve the problem of spiral arms getting wound-up too quickly. Another feature of this density wave is that the clouds of gas and dust get a bit compressed at the edge of the arm the enter at. This helps start their collapse leading to the formation of new stars. The newly formed stars will then continue through the arm but only the longer lived ones will make it out. The result is that short lifetime stars are mainly to the spiral arms.

The density wave idea seems to agree with observations of spiral arms in many galaxies and is the preferred explanation, but there are still some questions that need answers such as how do you set up a spiral arm in the first place.

Posted in astro blog by Stuart on Sunday 15th Jan 2006 (23:42 UTC) | Permalink

Stardust re-entry

The sample return capsule of the Stardust spacecraft is due to land in a little under 10 hours at 10:05am GMT. Before that, in about four hours, the capsule will be remotely released and head towards the USA, entering the atmosphere at 9:57am GMT. If you live in the western states, you may have a chance of seeing the re-entry - it will be the middle of the night and should look impressive as it slams into the atmosphere at about 48,000 km/hour (28,800 miles/hour). It will be the fastest re-entry of any recorded man-made object. Worth looking out for.

If you live in Florida you shouldn't be disappointed about missing Stardust re-entry as you should get the chance to see the launch of the New Horizons mission as it heads off to Pluto. The launch window is set for the afternoon (local time) on Tuesday. Does anyone out there know the maximum distance away from the launch site that you can still see the launch from?

Posted in astro blog by Stuart on Sunday 15th Jan 2006 (00:34 UTC) | Permalink


Today I visited the UK Swift Science Data Centre, at the University of Leicester, to learn how to analyse data from the Swift gamma-ray satellite. This satellite observes the universe at gamma-ray, x-ray and ultra violet energies and has three instruments: the Burst Alert Telescope (BAT), the X-ray Telescope (XRT) and the UltraViolet-Optical Telescope (UVOT).

Cassiopeia A in X-ray
The supernova remnant Cassiopeia A seen by the XRT instrument on Swift CREDIT: Swift/NASA
It was a very challenging day for me as I attempted to understand a whole new set of jargon and techniques that I am not used to. It was fun and I met some really interesting astronomers in the process.

The excellent folks that were training us spend a lot of their time on call and have to drop everything if the BAT detects a gamma-ray burst (GRB). It seems that they have been especially busy this week as they have had six GRBs to deal including two on the same day.

Posted in astro blog by Stuart on Saturday 14th Jan 2006 (01:13 UTC) | Permalink

Youngest binary pulsar

Considering all the great stuff that has been announced at the AAS meeting, I haven't seen anyone mention the discovery of the youngest binary pulsar found to date.

A pulsar is an end-product of a large star (large compared to the Sun) exploding as a supernova; while the outer parts of the exploding star blast off into space, the middle collapses down to form a rotating neutron star. If the magnetic fields are strong enough, these neutron stars will emit beams of radio waves and are the radio-wave equivalents to lighthouses. This flashing (or ticking if you connect your radio telescope to a speaker) nature gives them the name pulsar.

There are around 1700 pulsars known to date, many of which have companions. These are known as binary pulsars and should not be confused with the double pulsar. The latest discovery is exciting because the pulsar in the binary system seems to be only about 112,000 years old. That is very young by the standards of astronomers. In fact, it is only slightly younger than the modern human - Homo sapiens sapiens - is thought to be. Finding such a young binary pulsar suggests that these systems may be more common than was previously thought (although it may just be chance) and this provides good news for the gravitational wave detectors such as GEO600, LIGO and LISA.

These instruments are (and will be) trying to detect very slight ripples in the fabric of space caused by large moving masses such as neutron stars or black holes. This is a painfully difficult thing to do because the ripples are so tiny and you have to seriously dampen out oscillations if you are to stand a chance of detecting anything. Despite the gravitational wave astronomers improving their instruments enormously over recent years they are still a long way off being able to detect anything. But, the pulsar observations help from the other direction. The new result hints that there may be more binary pulsars than were thought, so there will be more gravitational waves out there to be detected. Hopefully, in the not-too-distant future, a gravitational wave will be detected and then we will have a whole new window on the universe.

Posted in astro blog by Stuart on Saturday 14th Jan 2006 (00:41 UTC) | Permalink

The 100 top...

In the UK, Channel 4 have been making a seemingly never-ending number of programmes called "The 100 best....". I am told that next week they will broadcast "The 100 Hottest Web Searches
2005". This in itself may not be very interesting, but one of those top 100 searches (possibly between 60 and 80 from the sounds of it) is for the term "aurora borealis". This is not surprising considering the show the Sun gave last year. Apparently the good folks at the University of Lancaster's Aurora Watch were filmed for the programme.

Posted in astro blog by Stuart on Friday 13th Jan 2006 (00:30 UTC) | Permalink

The orbit of Venus

I've been quiet for the last few days partly because I've been busy, but also because I assume you will all be reading the live blogging from the AAS 207th meeting. There is a lot of exciting stuff happening there and Aaron, Pamela, Travis and Phil are doing a great job of communicating that. However, on a different point, I just saw an animation on APoD (via Rob at Dirty Skies) showing the change in the phase and size of Venus created with real images taken during 2004 and the end of 2005. The animation is simply amazing. If ever you doubted that Venus went around the Sun, this is for you. Even if you didn't, you should still have a look at it. This was one of those moments where the universe gave me a slap on the face to remind me how fantastic it is.

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Posted in astro blog by Stuart on Thursday 12th Jan 2006 (12:11 UTC) | Permalink

AAS 207th meeting

The American Astronomical Society or AAS (pronounced double A S) 207th meeting will be on from Sunday 8th to Thursday 12th in Washington D.C.. I won't be there, but there are other astronomy bloggers who will be. Aaron, Pamela and Travis of Slacker Astronomy will be live blogging as will be the folks at SCSU Astronomy. With at least 2748 people registered so far, there will be a lot of new results coming out this week.

Posted in astro blog by Stuart on Sunday 08th Jan 2006 (02:22 UTC) | Permalink

The size of Charon

In this week's edition of Nature, there is a report detailing observations of Pluto's moon Charon occulting a background star. The observations were made using part of the Very Large Telescope, the 0.5m Campo Catino Austral Telescope and the 2.5m Jorge Sahade telescope which are all based in South America.

At each of the three sites they saw the star passing behind a different part of Charon and this allowed accurate measurements of the diameter. The diameter is now found to be 603.6 km (±5.0km) which is incredibly accurate for a measurement of something so far away. Once you have a diameter for Charon you can also combine that with the mass of the moon to work out the average density. It turns out to be about 1.7 gm/cm³ which is equivalent to "an icy body with about slightly more than half of rocks". You can listen to this on the Nature podcast or read the ESO press release for more details.

Pluto is making the news quite a lot at the moment. It should get even more exciting soon as the first mission to Pluto should be launching in about 12 days time.

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Posted in astro blog by Stuart on Thursday 05th Jan 2006 (08:51 UTC) | Permalink

Happy Perihelion!

Today is quite a special point in the year. Obviously, it isn't the start of the calendar year (that was Jan 1st) and it isn't an equinox (those are on March 20th and June 21st this year). It is actually the point when the Earth is closest to the Sun in its orbit. In fact, according to the US Naval Observatory, that is due to occur at roughly 15:00 Universal Time (currently the same as GMT) which is … right now!

The Earth's orbit is slightly elliptical, so for some of the year it is closer than the average distance from the Sun and at other points it is slightly further away. The point in the orbit where the separation is greatest is known as aphelion and the closest approach - happening right now - is perihelion.

At this moment in history, the Earth is closest to the Sun during winter in the northern hemisphere which makes it slightly warmer than it would be if we were on a circular orbit. By the same reasoning, the southern hemisphere experiences slightly hotter summers too. But all this will change in time because of the precession of the Earth's axis (it tilts at 23.5 degrees). In about 13,000 years the northern hemisphere will be tilted towards the Sun during perihelion and summers (for us northern hemisphere folk) will be a bit hotter and the winters a bit colder.

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Posted in astro blog by Stuart on Wednesday 04th Jan 2006 (15:25 UTC) | Permalink

Orion's sword

In the ancient Greek legend, Orion was a hunter. In fact he was such an important character that a constellation was named after him.

The constellation of Orion is prominent in the winter night sky and is found by looking for the three stars in a line that make up Orion's belt. From the belt hangs a small sword (or dagger) and with the unaided eye this usually looks like a few faint stars and smudge of light. Back in December I took several 15 second exposures of the sword using my digital camera set to full zoom. I had forgotten about them, so I've only just got around to adding the frames together. To take the pictures I placed my camera on a mini tripod which remained fixed during each exposure. Despite each exposure lasting only 15 seconds the apparent movement of the stars, due to the Earth's rotation, causes the stars to look like lines.

Sword of Orion
Orions sword. Created by adding six 15 second exposures. CREDIT: Stuart
In the middle of the sword you can even make out the smudge that is M42 - the Orion Nebula. My image isn't as brilliant or as beautiful as some, but I'm still impressed by such a simple setup.

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Posted in astro blog by Stuart on Tuesday 03rd Jan 2006 (21:06 UTC) | Permalink
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