Charles Thomas Kowal (November 8, 1940 – November 28, 2011) was an American astronomer known for his observations and discoveries in the Solar System. As a staff astronomer at Caltech's Mount Wilson and Palomar Mountain observatories between 1961 and 1984, he found the first of a new class of Solar System objects, the centaurs, discovered two moons of the planet Jupiter, and discovered or co-discovered a number of asteroids, comets and supernovae. He was awarded the James Craig Watson Medal for his contributions to astronomy in 1979.
In the 1960s, Kowal observed with the Palomar 48" Schmidt telescope, contributing observations to noted cosmologistFritz Zwicky's six-volume Catalogue of Galaxies and of Clusters of Galaxies.[nb 1] Kowal also began to search for Type Ia supernovae in other galaxies, in an effort led by Zwicky to calibrate the magnitudes of these exploding stars so that they could be used as standard candles, reliable measures of the distance of their host galaxies (work which in the present has led to accurate measurements of the expansion of the universe).[3] In the course of these Palomar supernovae surveys with the 48" Schmidt,[4] Kowal personally discovered 81 supernovae, including SN 1972e.
Kowal provided observations of new Solar System discoveries and reports of new supernovae via the IAU circular system throughout the 1970s,[6] and searched for new objects. He discovered two moonsofJupiter: Leda in 1974 and Themisto in 1975, the 13th and 14th moons of Jupiter to be found.[7] Themisto was later lost (i.e. its orbit was not known well enough to reobserve it) and was not rediscovered until 2000.
Between December 1976 and February 1985, Kowal searched 6400 square degrees of sky in the ecliptic plane for distant, slow-moving Solar System objects.[8] Only one object was found beyond Jupiter: 2060 Chiron, discovered in 1977, which had the unusual characteristic of features both like an asteroid and a comet. It became recognised as the first object in the centaur class after a second one was discovered 15 years later. Centaurs are objects with unstable orbits which orbit between Jupiter and Neptune. They are probably drawn in from the Kuiper belt by alignments with larger planets. Chiron remains one of the largest such worlds known, and one of a handful that have a comet-like coma.
Kowal also discovered or co-discovered the periodic comets 99P/Kowal, 104P/Kowal, 134P/Kowal-Vavrova, 143P/Kowal-Mrkos, and 158P/Kowal-LINEAR.
Kowal moved to the new Space Telescope Science Institute in 1985, where he monitored the instruments of the Hubble Space Telescope as one of the operations astronomers. His book Asteroids: Their Nature and Utilization was published in 1988, and a second edition in 1996.
^The 48" Schmidt was then fully automated, and used for a successor survey, the Near Earth Asteroid Tracking (NEAT) survey, which ran on the Schmidt from April 2001 to April 2007.
