Using Meteors to watch Polish TV

September 27, 2007

One man’s poison is another man’s meat. One man’s noise is another woman’s project. Radio telescopes see some odd things. Amateur astronomers miss half the best meteor showers. Polish TV is a nuisance. Or is it ? As Goethe said, connect, only connect. (Or was it E.M.Forster ?)

On Wednesday I was attending a meeting of the LOFAR-UK consortium. LOFAR is a project to construct a low frequency radio telescope array several hundred km across. It’s basically a Dutch project, but they are bringing foreign partners on board, partly to raise money and partly to expand the baselines. The UK consortium is planning several possible stations in the UK, maybe including one just outside Edinburgh, near where Dolly the Sheep was cloned. (A LOFAR station is hard to recognise as a telescope, being a collection of mesh tiles and odd looking metal spiders in a field…but all connected to an ultra-fast fibre link.)

LOFAR is appealing to a broad range of scientists. Years back, classical radio astronomy was entirely about exotic and violent things like quasars and pulsars, gravitationally collapsed and/or squirting out relativistic plasma. But now its part of the mainstream, with useful data on the interstellar medium, the early universe, star formation, stellar coronae, etc. Now the solar physicists and the space plasma folk are really interested too.

Ger De Bruyn gave a talk showing results from the first test station in the Netherlands. They made a map of the whole Northern Sky, and rediscovered the same sources Cambridge radio astronomers found in 1959. So far so good. But he also showed lots of raw data showing all the artefacts and radio frequency pollution you have to deal with. Some of this is cute. As Low Earth Orbit Satellites fly past, you can see them change frequency due to the Doppler effect. Some of it is very loud noise – Cas A and the Sun are horribly bright, and the Sun has a nasty habit of flaring erratically, as he showed in some data with 21 msec resolution. Suddenly Lyndsay Fletcher from Glasgow got excited. “Ooo give me that data” says she. “Are you sure?” says Ger, “its just a test run to see if we can clean the data”. “Yes I am sure” says Lyndsay, “we’ve got data at every other wavelength on the same flare – this is the missing link”. OK – science with LOFAR has started !

Next Ger showed how at one frequency Danish TV gets in the way, and at another frequency its Polish TV. (77 MHz if you want to tune in). The plot had a whole bunch of spikes. “That” says he “is the Perseid Meteor Shower”.

Being a dumb X-ray astronomer at heart I checked this with old hand Adrian Webster. Was the Polish TV signal really bouncing off the meteors ? Not quite, it seems. The meteors create an ionised trail as they burn through the atmosphere, and it is these trails which reflect the radio waves. So is this a discovery ? Nope, says Adrian. Bernard Lovell found the same thing at Jodrell in the 1950s, and claimed that all the best meteor showers were in the daytime…. There is a website run by the Marshall Space Flight Center which has a good explanation, and where you can even listen to radio meteor trails.

Ok, so I am catching up. Its still new to me. But the more I think about it the more bizarre and beautiful it seems. We bring together a field full of wire that can look at the edge of the Universe and an oscillating signal encoding pictures of people in Poland, and suddenly we can see small pieces of rock, unaltered for four billion years, finally streaking into oblivion above our heads.