Thursday, 21 October 2010

48 hour exposures

An image from the Hubble deep-field telescope has revealed the most distant, and therefore oldest, object ever discovered. It is a galaxy known as UDFy-38135539. A small one, but a galaxy nonetheless and the light from it has taken over 13 billion years to reach us; starting its journey only 600 millions years after the big bang. It is also receding so quickly that its light is red-shifted by a factor of 8.6, such that any visible light is shifted down to the deep infrared. You can see the starfield image on the ESO web site. The story on the BBC web site reveals that this was a 48 hour exposure and the ESO web site tells us that the teams responsible were NASA, ESA, G Illingworth (UCO/Lick Observatory and University of California, Santa Cruz) and the HUDF09 Team.

Lick Observatory has historically played a significant part in our infrared imaging story. During the 1920s and 30s scientists at the observatory experimented with infrared photography, as I mentioned in an earlier post. The infrared comparison photos that WH Wright took of Mars in 1924, which proved that Mars has an atmosphere to speak of, were taken there (and are included in the Infrared 100 exhibition at the RPS in Bath this month). If you're interested there is a 2006 paper on the Lick photographs in the Journal of Astronomical History and Heritage (Vol 9, No 2, p 181-184) but it's not available online.

And the 48 hours? There's a delicious coincidence which brings me to another historic infrared photograph taken at another famous American observatory, Mount Wilson. In this case the date is 1930, the photographer is HD Babcock and it is a blurry and unassuming image of some objects on a shelf. It is also the first photograph taken in total darkness.

Infrared photograph taken in total darkness by HD Babcock in 1930
I had a telephone conversation with an archivist at Mount Wilson but, so far, we have been unable to find out whether a real copy of this photo still exists. The one you see here is taken from an old edition of Clark, who says that the 'light' source was one or more under-run electric heaters. The plate was sensitised with neocyanine and the exposure was 48 hours at f/2.

So here we have the darker recesses of the universe, one distant and one very close. Both unobservable except using infrared imaging and both taking 48 hours to shoot.

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