In 2004 and 2005, the Cosmic Evolution Survey was granted almost 1000 hours of observing time on the Hubble Space Telescope . COSMOS, an international collaboration of some 90 astronomers headed by Nick Scoville of Caltech, used this extraordinary allotment of scarce HST time to peer at very distant galaxies in a patch of sky about nine times as big as the full Moon.

Not far from the North Pole of our own galaxy, this patch was chosen for its relative freedom from obscuring foreground stars, dust, and local galaxies. The COSMOS exposure has yielded well measured positions and shapes for half a million galaxies out to a redshift z of 3. That's a glimpse all the way back to how galaxies looked 11 billion years ago.

Having completed a gravitational-lensing analysis of that prodigious accumulation of observational data, the collaboration has now reported the most extensive and detailed study...

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