First light (astronomy)

This article is about the testing of telescopes. For the first light of dawn, see Twilight § Nautical twilight. For the cosmogonical age, see first light (cosmology).

In astronomy, first light is the first use of a telescope (or, in general, a new instrument) to take an astronomical image after it has been constructed. This is often not the first viewing using the telescope; optical tests will probably have been performed to adjust the components.

First light image from the Kepler space telescope^[1]

Characteristics

Hubble Space Telescope's first light with its impaired WFPC, 1990

The first light image is normally of little scientific interest and is of poor quality, since the various telescope elements are yet to be adjusted for optimum efficiency. Despite this, a first light is always a moment of great excitement, both for the people who design and build the telescope and for the astronomical community, who may have anticipated the moment for many years while the telescope was under construction. A well-known and spectacular astronomical object is usually chosen as a subject.^{[citation needed]}