Going Deep

Mercury, July/August 2003 Table of Contents

Image courtesy of NASA, ESA, and Tom M. Brown (STScI).

by Robert Naeye

In January 1996, Space Telescope Science Institute (STScI) director Robert Williams and several colleagues unveiled the deepest optical image of all time. The so-called Hubble Deep Field was a tunnel through time, revealing objects from foreground Milky Way stars to subgalactic clumps less than 1 billion years after the Big Bang. Hubble acquired the image over 10 days by "staring" at a field in Ursa Major the size of a sand grain held at arm's length. The Deep Field captured objects down to 30th magnitude, about the brightness of a cigar’s glow on the Moon as seen from Earth.

Now, thanks to the newly installed Advanced Camera for Surveys, Hubble has taken an even deeper image. Tom Brown of STScI and colleagues directed the Space Telescope to image an area in the halo of the Andromeda Galaxy. With its enhanced sensitivity, the new camera needed only 3.5 days to acquire the image, which shows objects down to 31st magnitude. That’s 10 billion times fainter than the faintest stars you can see with your naked eye.

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