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James Edward Keeler (September 10, 1857–August 12, 1900) was an American astronomer.

Keeler worked at Lick Observatory beginning in 1888, but left after being appointed director of the University of Pittsburgh's Allegheny Observatory in 1891. He returned to Lick Observatory as its director in 1898, but died not long after in 1900. He had married in 1891 and left a widow and two children.

Along with George Hale, Keeler founded and edited the Astrophysical Journal, which remains a major journal of astronomy today.

Keeler was the first to observe the gap in Saturn's rings now known as the Encke Division, using the 36-inch refractor at Lick Observatory on 7 January 1888. After this feature had been named for Johann Encke, who had observed a much broader variation in the brightness of the A Ring,^[1] Keeler's contributions were brought to light^[2]. The second major gap in the A Ring, discovered by Voyager, was named the Keeler Gap in his honor.

In 1895, his spectroscopic study of the rings of Saturn revealed that different parts of the rings reflect light with different Doppler shifts, due to their different rates of orbit around Saturn.^[3] This was the first observational confirmation of the theory of James Clerk Maxwell that the rings are made up of countless small objects, each orbiting Saturn at its own rate.

Keeler discovered two asteroids, one in 1899 and one in 1900, although the second was lost and only recovered about 100 years later.

He won the Henry Draper Medal in 1899.

In 1880, Allegheny Observatory director Samuel Pierpont Langley, accompanied by Keeler and others, went on a scientific expedition to the summit of Mount Whitney. The purpose of the expedition was to study how the Sun's radiation was selectively absorbed by the Earth's atmosphere, comparing the results at high altitude with those found at lower levels. As a result of the expedition, a 14,240-ft. peak near Mount Whitney was named the "Keeler Needle".

In addition to the Keeler Gap in Saturn's rings, craters on Mars and the Moon are named in his honor, as is the asteroid 2261 Keeler.

1. ^ David M. Harland, Mission to Saturn: Cassini and the Huygens Probe, Chichester: Praxis Publishing, 2002.
2. ^ D.E. Osterbrock and D.P. Cruikshank, "J.E. Keeler's discovery of a gap in the outer part of the A Ring", Icarus 53, 165-173 (1983)
3. ^ J.E. Keeler, "A spectroscopic proof of the meteoric constitution of Saturn's rings", Astrophysical Journal 1, 416-427 (1895)

• Campbell, W.W. (November 1900). "James Edward Keeler". ApJ 12: 239-253. doi:10.1086/140764.  obituary, includes extensive list of published writings
• H. H. T. (February 1901). "List of Fellows and Associates deceased during the past year". Monthly Notices of the Royal Astronomical Society 61: 197-199. 

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