A member of a class of eclipsing variable stars in which the two components are stars of spectral type F or G that are similar in brightness and almost in contact. The primary and secondary minima of the light curve are nearly equal and the periods are typically several hours.

Cepheid variable.

A type of German radar dish used from 1944 in the UK and the Netherlands for the first systematic observations in radio astronomy.

A large, flat-floored lunar crater, particularly one that has been flooded by lava.

The part of the cycle of the Moon’s phases when the illuminated fraction of the visible disc is decreasing. The opposite is waxing.

English name for the constellation Aquarius.

The group of stars Gamma γ, Eta η, Zeta ζ and Pi π in the constellation Aquarius, normally shown as the Water Carrier’s jar in representations of the mythological figure associated with the constellation.

English name for the constellation Hydra.

The shortest distance between two points in a wave train that have the same phase.

The part of the cycle of the Moon’s phases when the illuminated fraction of the visible disc is increasing. The opposite is waning.

Wolf-Rayet Star.

Comet West.

A Dutch national radio astronomy observatory which is part of the Netherlands Foundation for Research in Astronomy NFRA, or ASTRON. The administrative headquarters are at Dwingeloo Observatory. The instrument at Westerbork Observatory is called the Westerbork Synthesis Radio Telescope WSRT. It is a fourteen-element aperture synthesis instrument, and came into operation in 1970. A major extension in 1980 increased the baseline from 1,500 to 3,000 metres 0.9 to 1.8 miles.

English name for the constellation Cetus.

Fred Lawrence Whipple Observatory.