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

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 in 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 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.

For example, the 5.08-metre (200 in) Hale Telescope saw first light January 26, 1949, targeting NGC 2261[2] under the direction of American astronomer Edwin Powell Hubble. The image was published in many magazines and is available on Caltech Archives.

The Isaac Newton Telescope had two first lights: one in England in 1965 with its original mirror, and another in 1984 at La Palma island.[3] The second first light was done with a video camera that showed the Crab Pulsar flashing.[4]

Elation at first light images by the Hubble Space Telescope in 1990 soon gave way to disappointment when a flaw prevented adjustments for proper operation.

The Large Binocular Telescope had its first light with a single primary mirror on October 12, 2005, which was a view of NGC 891.[5][6] The second primary mirror was installed in January 2006 and became fully operational in January 2008.[7]

The 10.4 m Gran Telescopio Canarias had a first light image of Tycho 1205081 on 14 July 2007.[8]

The IRIS solar space observatory achieved first light on July 17, 2013.[9] The PI noted, "The quality of images and spectra we are receiving from IRIS is amazing. This is just what we were hoping for ..."[9]


In physical cosmology, first light refers to the light emitted from the first generation of stars, known as population III stars, which formed within a few hundred million years after the Big Bang.[10]

These stars were the first source of visible light in the universe, apart from a brief period very early on, when it first became transparent and was briefly filled with a brilliant pale-orange 4000K glow during recombination and photon decoupling, at about 377,000 years of cosmic time. However, the photons from decoupling only provided visible light for very few million years, since they were quickly redshifted to infrared and then radio/microwave frequencies, by the expansion of the universe. The first stars were therefore the first occasion when the kind of light now seen, appeared in the universe.



  1. ^ Atkinson, Nancy. "Kepler's "First Light" Images". Universe Today. Retrieved 13 October 2012.
  2. ^ Kardel, Scott (2009-01-26). "January 26: 60th Anniversary of Hale Telescope "First Light"". Retrieved 2012-02-04.
  3. ^
  4. ^ Information, Reed Business (16 February 1984). "New Scientist". Reed Business Information. p. 16.
  5. ^ Archived December 2, 2008, at the Wayback Machine
  6. ^ "Large Binocular Telescope Successfully Achieves First Light". 2005-10-26. Retrieved 2012-02-04.
  7. ^ "Giant telescope opens both eyes". BBC News. London. March 6, 2008. Retrieved 2008-03-06.
  8. ^ "First Light for the Gran Telescopio Canarias". 14 July 2007. Retrieved October 3, 2015.
  9. ^ a b Zell, Holly (9 March 2015). "IRIS Telescope's First Look at Sun Atmosphere".
  10. ^ Ellis, Richard. "Searching for first light in the Early Universe". Retrieved 2007-01-21.