A collective name for a group of subatomic particles including protons and neutrons together termed nucleons and a number of particles of short half-life that produce a nucleon when they decay.

A volcanic igneous rock, consisting primarily of the silicate minerals pyroxene and plagioclase.

A member of a group of meteorite types, including eucrites and howardites, which are similar to terrestrial basalts. See also: achondrite.

A large, shallow, circular structure on the surface of a planet, created by the impact of a large meteorite. Basins may show concentric rings; some have been filled in by lava in subsequent volcanic activity. See also: crater.

The letters of the Greek alphabet, used in conjunction with constellation names as in Alpha Leonis, to identify the brighter stars. Johann Bayer 1572-1625 was responsible for compiling the first complete star atlas, called Uranometria, which was published in 1603. In it he introduced the system of naming the brighter stars in each constellation by Greek letters, which he allocated approximately according to brightness or, in some instances, in order of position on the sky. The system was rapidly adopted and is still in use today

Abbreviation for Bonner Durchmusterung.

A B star that shows emission lines of hydrogen superimposed on the absorption lines in its spectrum. Supergiants, which may also show such emission, are excluded from this classification.

The area of sky being observed at any one time by a radio telescope.

The angular extent of the beam of a radio telescope. The half-power beamwidth is the angular extent over which the power received is at least half the maximum measured when the radio telescope points directly at a point source. It gives a measure of the resolving power of the antenna.

A name sometimes given to the galaxy NGC 2537.

English name for the constellation Boötes.

One of the brightest of all astronomical sources of infrared radiation. It was discovered by Eric Becklin and Gerry Neugebauer in 1967 and is located in the Kleinmann-Low Nebula, within the Orion Nebula. It is thought to be a very young, massive star of spectral type B, hidden behind so much dust that it appears very feeble in visible light. There are other infrared sources near by in what is believed to be a region of very active star formation.

English name for the open star cluster Praesepe.

The astrophysical research institute of the Chinese Academy of Sciences, founded in 1958. Facilities for radio astronomy, optical astronomy, solar observations and time-keeping are located at five observing stations.

One of the small satellites of Uranus discovered during the Voyager 2 encounter with the planet in 1986.