A pulsating variable star that changes in brightness slowly and in an irregular way. Such stars belong mainly to spectral types K, M, C and S.

Abbreviation for Infrared Telescope Facility.

A 2.5-metre 98-inch reflecting telescope in the Isaac Newton Group at the Observatorio del Roque de los Muchachos, La Palma, Canary Islands. It is operated by the Royal Greenwich Observatory. Observing time is shared between the collaborating countries, which are the UK, Spain and the Netherlands. The telescope was originally installed at Herstmonceux, the UK base of the Royal Greenwich Observatory until 1990. It was rebuilt and provided with a new primary mirror on removal to La Palma, where it came into operation in 1984.

The Japanese national space agency.

Abbreviation for International Sun-Earth Explorer.

One of the major upland areas on the planet Venus, comparable in size with the continent of Australia. It includes the highest mountain peaks on Venus, Maxwell Montes.

An obsolete term, formerly used to mean a giant galaxy. It is associated particularly with the philosopher Immanuel Kant 1724-1804, who introduced it in 1755. It was used until the 1920s in popular writing.

Abbreviation for interstellar medium.

Abbreviation for Infrared Space Observatory.

A line connecting points of equal light intensity on a map showing the distribution of brightness over, for example, an area of sky.

The property of being the same in every direction. Liquid water is isotropic, whereas a snowflake, which has sixfold symmetry, is not. The universe on the largest scales is believed to be isotropic. It is observed to be expanding isotropically to a high degree of precision, and the cosmic background radiation is equally isotropic.

Abbreviation for International Ultraviolet Explorer.

Asteroid 1627, diameter 6.2 km, discovered in 1929 by Ejnar Hertzsprung. It is a member of the Amor group.