First light

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For the book by Richard Preston, see First Light (book).

First light through the Hubble WFPC

First light, in cosmology, refers to the first light emission, billions of years ago, moments after the big bang. ^[1]

In astronomy, first light is when a telescope (or, in general, a new instrument) is first used to take an astronomical image after it has been constructed. This is not often the first viewing using the telescope; optical tests have likely already been performed during daylight to adjust the components. The first light image is normally of little scientific interest and is of poor quality since the various telescope elements must be adjusted for optimum efficiency. Usually, a well-known and spectacular astronomical object is chosen. Despite this, a first light is always a moment of great excitement, both for the people who designed and built the telescope, and for the astronomical community.