Any roughly circular or spherical distribution of light or matter around another object. See also: galactic halo.

A star belonging to the population forming the galactic halo.

The brightest star in the constellation Aries. It is a giant K star of magnitude 2.0. The name is derived from the Arabic for sheep.

English name for the constellation Lepus.

A book by Johannes Kepler 1571-1630 published in 1619. It included the third of Kepler’s laws of planetary motion. Kepler himself believed his greatest achievement was the discovery of musical harmonies for the planets reflecting the divine harmony of the universe, and named the work accordingly.

A member of a class of galaxies characterized by their blue colour and narrow emission line spectra.

A test for the optical quality of a mirror. The mirror is covered with a screen in which there is a pattern of regularly spaced holes. The quality of the mirror can be judged from the image produced in the focal plane.

Henry Draper Catalogue.

The observatory of Harvard College, established in 1839. In 1847 it was equipped with a 0.38-metre 15-inch refracting telescope, which is still in its original building, the Sears Tower on Observatory Hill. In 1973, the Harvard-Smithsonian Center for Astrophysics was formed by combining the resources of the Smithsonian Astrophysical Observatory and Harvard College Observatory under one director, George Field.

Harvard College Observatory.

The full Moon nearest the time of the autumnal equinox. At this time of the year the inclination of the Moon’s orbit to the horizon is low and the Moon rises at approximately the same time each evening for a short period.

A radio astronomy observatory in California operated by the radio astronomy laboratory of the University of California, Berkeley.

An observatory in southern France, 100 km 62 miles north of Marseilles, at an altitude of 650 metres 2,100 feet in the foothills of the Alps. It was established in 1937 as a national facility for French astronomers and is owned by the Centre National de la Recherche Scientifique CNRS. The main instrument is a 1.93-metre 76-inch reflector which has been operated since 1958. A 1.52-metre 60-inch telescope, operating since 1967, is equipped only with a coudé focus and a modern spectrograph introduced in 1989. There are also 1.2-metre 47-inch and 80-centimetre 31-inch telescopes, and a 60/90-centimetre 24/36-inch Schmidt camera.

The evaporation of mini black holes. In general, black holes are an end-point for matter. However, Stephen Hawking showed that quantum physics allows mini black holes less than 10 to the power of -5 grams to evaporate matter and antimatter in equal quantities, possibly leaving a naked singularity behind.

The evolutionary track on the Hertzsprung-Russell diagram of a protostar, before it becomes a main-sequence star. The track shows the changes in luminosity and surface temperature that occur in the early phases of a star’s life. The exact position of the track on the diagram depends on the star’s mass. Hayashi tracks are named after the Japanese astrophysicist, Chushiro Hayashi, who pioneered the theoretical work in the 1960s.