spaces in the radial distribution of asteroids due to commensurabilities and resonances of orbital period with that of Jupiter. There are notable gaps corresponding to orbital period ratios of 4:1, 3:1, 5:2, 7:3 and 2:1. Any asteroids formerly in such orbits would be perturbed by regular gravitational interactions with Jupiter. The explanation was first given by Daniel Kirkwood in 1857. However, beyond 3.5 AU from the Sun, resonances correspond not to gaps but to isolated groups of asteroids at ratios of 3:2, 4:3 and 1:1. The reason for this is not fully understood.

A mountain-top observatory site near Tucson, Arizona, which is home to one of the largest collections of astronomical research instruments in the world. These include the Kitt Peak National Observatory, facilities of the US National Solar Observatory, and the WIYN Telescope operated by the US National Optical Astronomy Observatories. A number of universities and other research organizations also lease space on Kitt Peak for astronomical work.

A facility of the US National Optical Astronomy Observatories located at Kitt Peak in Arizona. The largest telescope is the 4-metre 160-inch Mayall Telescope. The other instruments include a 2.1-metre 82-inch telescope and the Burrell Schmidt camera.

An extended source of infrared radiation in the Orion Nebula. It is a region of star formation in the central dark part of the nebula, lying behind the optically luminous gas.

Comet Kohoutek.

One of the Hirayama families of asteroids, at a mean distance of 2.88 AU from the Sun. The members are very similar silicaceous types and are presumed to come from the break-up of a single parent body about 90 km 56 miles in diameter. The largest member is 208 Lacrimosa, which is about 45 km 28 miles in diameter. The family is named after 158 Koronis, diameter 35 km 22 miles, discovered in 1876.

Abbreviation for Kitt Peak National Observatory.

An acronym given to a group of basaltic rocks found on the Moon, which are particularly rich in potassium symbol K, rare earth elements REE, and phosphorus P, though the composition varies widely between different types. Samples of KREEP were returned from the Oceanus Procellarum by the Apollo 12 mission. These were rich also in uranium, thorium and zirconium.

sungrazer.

A faint binary star in the constellation Cepheus. The two members of the system, magnitudes 10 and 11, orbit each other in a period of 44 years. Since the orbit is seen face on and the two stars are easily resolved, the relative motion shows clearly in photographic sequences taken over a period of decades. Both are dwarf M stars and the fainter component is a flare star. At a distance of 13 light years, it is one of the nearest stars to the solar system.

Abbreviation for Kennedy Space Center.

A 0.915-metre 36-inch Cassegrain reflecting telescope mounted in a Lockheed C141 Starlifter jet transport aircraft, which was operated between 1975 and 1996 by NASA as a national facility in the USA. It was based at NASA’s Ames Research Center, Mountain View, California. Important discoveries made with the observatory include the ring system around the planet Uranus. Its replacement, SOFIA, is due to begin operations in 2001.

A population of small icy bodies, similar in size to asteroids, occupying a ring-shaped region in the plane of the solar system extending from the orbit of Neptune 30 AU from the Sun out to possibly 100 or 150 AU. This population, members of which are variously described as Kuiper Belt objects, trans-Neptunian objects or ice dwarfs, is believed to be the source of short-period comets. The name of Gerard Kuiper, a distinguished Dutch-American planetary scientist, became associated with the belt because, in 1951, he predicted its existence from theoretical work on the origin of the planetary system. However, an Irish writer and theorist, Kenneth E. Edgeworth, had published similar arguments in 1943 and 1949. In recognition of his contribution, the belt is also sometimes termed the Edgeworth-Kuiper Belt. The first observational evidence for the existence of the Kuiper Belt was the discovery in 1992 of the faint object known as 1992 QB1 in a near-circular orbit about 50 AU from the Sun. About 30 further objects in similar orbits were found in the following few years. It has been suggested that Pluto is the largest member of the Kuiper Belt.