One Million Second Camera Exposure

Really. Back in 2004 when the Hubble telescope took the immediately famous Ultra Deep Field image, it required over 800 21 minutes exposures taken over a 4 month period and 400 orbits. That's 1,000,000 second exposure.

Collecting photons for that long period, the telescope's Advanced Camera For Surveys (ACS) was able to see back to within 5% of the beginning of time, the Big Bang. The youngest galaxies visible in the image (circled) emerged about 800 million years after the Big Bang. Over 10,000 galaxies appear in the Hubble image.



In order to take images of distant, faint objects, Hubble must be extremely steady and point very accurately. The telescope is able to lock onto a target without deviating more than 7/1000th of an arcsecond, or about the width of a human hair seen at a distance of 1 mile. That's the same as keeping a laser pointer steady on a dime that's 200 miles away.

The Hubble Ultra Deep Field is called a "pencil beam" survey because the observations encompass a narrow piece of sky. It would take about 50 Ultra Deep Fields to cover an area the size of the Moon. For Hubble to observe the entire sky in the same way, it would take almost 1 million years of uninterrupted observing.

Hubble's keen vision, its resolution, is equivalent to reading the date on a quarter that's a mile away.

The ACS recently experienced an apparent electrical short and probably can't be fixed from the ground or even by the next Shuttle repair mission in September 2008.

To see the Hubble in your night sky go here, for a schedule.

TH

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