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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 uses a wide assortment of telescopes/observatories operating across the electromagnetic spectrum including the Chandra X-ray Observatory, XMM-Newton, Far Ultraviolet Spectroscopic Explorer (FUSE), the Hubble Space Telescope, the Infrared Telescope Facility, and the Very Large Array, and optical telescopes including Keck, Lick, and Kitt Peak.
Between 1900 and 1908, he accompanied four eclipse expeditions and was in charge of the one sent from Lick Observatory to Sumatra in 1901.