First light

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

First light through the Hubble WFPC

First light is when a telescope is first used to take an astronomical image after it has been constructed. The term is also sometimes used to refer to the first image taken with a new instrument.

The term is also used in amateur astronomy to refer to the first use of a telescope for astronomical viewing. 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.

In cosmology, First Light also refers to the moment, millions of years after the big bang, when stars and galaxies first formed out of a dark universe.^[1]