Visible from space

I was getting my hair cut this morning when I heard an advert on the radio claim that the only man-made structure visible from space was the Great Wall of China. I chuckled to myself and told the hairdresser that it wasn't true. I told him about the first Chinese astronaut, Yang Liwei, to be launched by the China National Space Administration last October. He orbited for 21 hours but didn't manage to see the Great Wall. Astronaut Eugene Cernan claims you can see it (or possibly the shadow cast by it) while astronauts William Pogue and Jay Apt claim not to have seen it.

So does that mean that astronauts can't see any man-made objects from space? Not quite. It depends on how big something is and whether they are using a pairs of binoculars! To make out details of something it is important to have a high enough resolution, although it is quite possible to see something smaller is there if there is enough contrast with the background. After all, the angular size of stars is extremely small but we can still see that they are there - we just can't make out any details on them.

So to round up, we can see man-made objects from space if there is enough contrast between them and their surroundings or if we use a pair of binoculars or a small telescope. The wall can also be 'seen' by radar. However if we can make out the Great Wall of China, we should also be able to see the M62!

Posted in astro blog by Stuart on Wednesday 26th May 2004 (13:03 UTC) | Permalink

Armageddon

When all the big asteroid films came out a few years ago, I somehow managed to miss Armageddon. From what I saw of the reviews I didn't miss much. Last night it was on Channel 5 in the UK so I thought I would see what I made of it. How wrong can the physics be? It was awful. Gravity (or lack of) was only taken into account when they felt like it - they spent most of their time in space seemingly working with 1g (the same as on Earth). This was true in both the MIR space station (even if they did try to get around it by spinning MIR up) and also on the asteroid which was only the size of Texas. At one point they claimed the asteroid would have a similar gravity to the Moon (wrong) which itself provides only about 1/6th as much as we experience at the Earth's surface. Someone send the makers a G.C.S.E science text book please.

At the very start I also noticed that they had the Moon the wrong way round. The camera showed the near-side of the Moon before 'flying' past it to reveal the Earth inhabited by the dinosaurs. This is bad because the Moon is tidally locked with the Earth so that we only ever see one side - actually it slightly wobbles to let us see slightly around the edges. Even 65 million years ago it was locked so the near-side would still have been the near-side and therefore not visible in that shot. However, I was pleasantly surprised that they managed to get both the Earth and Moon in the same phase which shows that the computer simulation software at least knew some physics of light sources even if the film makers didn't.

Posted in astro blog by Stuart on Monday 24th May 2004 (19:16 UTC) | Permalink

The Core

I've just finished watching the DVD of "The Core" and wasn't too impressed by its physics. Phil Plait has a Bad Astronomy review of the film which discusses most of the problems. The most obvious is the premise for the whole film; the core of the Earth stops spinning causing all sorts of problems with Earth's magnetic field.

Now they don't say if it stops spinning completely or just relative to the crust. Either way, that means that a ball of iron the size of Mars just suddenly comes to a stop. Where does all that rotational energy go? Incidentally, it seems that the core takes only slightly less than one day to rotate 360° and so its motion relative to the crust is not as great as you might imagine. According to the Harvard Gazette it takes between 120 and 360 years for the core to 'lap' the crust which works out at about half a mile a day difference. Pretty slow really.

They also have 'beams of microwaves from outer space' which cause havoc in San Fransisco by destroying the Golden Gate bridge. These 'beams' are apparently let in by the collapsing magnetic field. Microwaves are just part of the electromagnetic spectrum - like light and radio waves - and are not kept away by magnetic fields. However, the Earth's magnetic field does keep out lots of charged particles such as high energy protons (usually found with neutrons in the centre of atoms). They tend to get focussed towards the Earth's poles and are what causes the northern and southern lights. Microwaves do reach us from space all the time although most of them are absorbed by water vapour and oxygen in the atmosphere. This fact is well known to astronomers who try to observe the cosmic microwave background radiation (CMB) at microwave frequencies. To get around the problem of absorption they have to find very high and dry sites (Tenerife, Chile or Antartica) or go into space. So losing our magnetic field doesn't cause dangerous 'beams' of microwaves and we probably wouldn't suffer too much from cosmic rays (protons and alpha particles) as the atmosphere does a pretty good job of stopping them too.

I did watch some of the extra features on the DVD which were quite interesting though. I like to see how special effects sequences are built up and there is one section where they describe simulating thousands of pigeons going crazy in Trafalgar square. They start hurling themselves at buildings (the pigeons not the special effects people) and passers by like 'pigeons of death'. However, the Director points out that one of the pigeons is in fact a fish and sure enough if you watch the scene there it is!

Posted in astro blog by Stuart on Sunday 23rd May 2004 (00:58 UTC) | Permalink

Zubenelgenubi

No I haven't just typed a random selection of letters on my keyboard! Zubenelgenubi is one of the most interesting star names that I know of (although Zubeneschamali comes close). Just the other week I noticed that zubenelgenubi.com had been bought up by one of those domain naming companies that just sit on the name hoping that someone will come along to pay them lots of money for it.

Anyway, enough of the complaints and back to the point. I just noticed that today's astronomy picture of the day shows Zubenelgenubi near the eclipsed Moon. The two Zubenes are in Libra and used to form the northern and southern claws of Scorpius.

Posted in astro blog by Stuart on Friday 14th May 2004 (16:57 UTC) | Permalink

The X Prize

The X Prize is a $10 million prize that is for the first private rocket to carry three people into space. For the purpose of the prize, space is defined as being 100 km (about 62 miles) above the surface which is still quite close by. Not only does the ship have to take the crew up and down safely, it has to repeat the whole process within two weeks. The point of this is to show that it is possible for a private organisation to build a reuseable launch vehicle which might lead to an explosion (sorry about the pun) in space tourism.

The latest news is that the Scaled Composities team have managed to reach an altitude of 64km (211,000ft). One of the UK's attempts in the competition is called StarChaser who had claimed that they would be about ready by 2003 but this clearly didn't happen - they currently seem to be taking their rocket on a tour of Britain. Various people say that the X Prize could be won within the next few months but I won't hold my breath just yet.

Posted in astro blog by Stuart on Friday 14th May 2004 (16:32 UTC) | Permalink

Transit of Venus

There is now less than a month to go until the transit of Venus; it starts at around 05:20 GMT on Tuesday 8th June. A transit is where a planet or moon passes directly in front of another object in the sky. In this case, Venus will pass infront of the Sun. The last time this happened was in 1882 so no currently living person has observed a transit of Venus. We are having a special transit party at Jodrell Bank.

On Friday we were filmed for a programme that will be shown, on the BBC, in the run up to the transit. The producer had us observing the Sun with the Lovell telescope in the background. The production crew were quite friendly and were from Screenhouse Productions in Leeds. We all had to sign release forms so they could show us on TV, but it seems that the Open University have big expansion plans as they plan to use the footage "throughout the universe".

Posted in astro blog by Stuart on Sunday 09th May 2004 (12:53 UTC) | Permalink
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