A star catalogue published by Yale University Observatory, including stars down to a nominal magnitude limit of 6.5.

The intensity of radiation from a source. Apparent brightness is the intensity of received radiation, which depends on the source’s distance and its true or absolute brightness. The brightness of astronomical objects is measured in magnitudes, and the word magnitude is commonly used as if it were synonymous with brightness.

A measure of the amount of radiation being emitted from a source. It is defined as the temperature a black body replacing the source would need to be at in order to produce the level of radiation actually observed. Brightness temperature is frequently used by radio astronomers as a measure of the intensity of radiation being received. It is a useful concept, since it indicates whether the source is emitting thermal radiation, in which case the source’s brightness temperature will be measured in hundreds or thousands of degrees, or synchrotron radiation, when the brightness temperature will be billions of degrees.

An organization founded in London in 1890 to promote and encourage popular interest in astronomy and practical work by amateur astronomers in particular. It publishes a bi-monthly journal and an annual handbook, organizes meetings and has a number of sections to coordinate observations undertaken by members. It has an autonomous branch in New South Wales, Australia.

An organization formed in 1933 to promote popular interest in the exploration and use of space. Its activities include publications and conferences.

A very cool star containing insufficient mass for nuclear reactions to be ignited in its core. A number of plausible candidate brown dwarfs have been identified. One of them, Gliese 229 B, has been shown to have water, methane and ammonia present, all of which would be destroyed in the hot atmosphere of a true star.

An intensity interferometer developed by R. Hanbury Brown and Richard Q. Twiss for measuring the angular diameters of bright stars. The first test results were announced in 1956. The only instrument of its type is the one they constructed at Narrabri in Australia. Two flux collectors, each 6.5 metres 21 feet in diameter and formed from several hundred smaller mirrors, were mounted on trolleys on a circular track with a radius of 94 metres 308 feet. The operating wavelength was 433 nanometres and the minimum diameter measurable about 0.0005 arc seconds. Of the order of a hundred stars were accessible, the faintest operating magnitude being 2.5. Diameters were estimated by analysing the correlation between intensity fluctuations at the two light collectors in relation to the separation between them.

A popular name for a faint, diffuse, luminous nebula NGC 7635 in the constellation Cassiopeia. Despite its apparently spherical shape, it seems not to have the characteristics of either a planetary nebula or a supernova remnant.

Asteroid 338, diameter 80 km, of the rare metallic type. It is the prototype of the Budrosa family of unusual asteroids, with six known members. They are grouped at 2.9 AU from the Sun with orbits inclined at 6° to the plane of the solar system.

A name given to the bipolar nebula NGC 6302 in the constellation Scorpius. No central star has been identified, but the central region is hot and active and gas is streaming outwards at velocities up to 400 km/s. The nebula appears red because much of its light is emitted as the red spectral lines of hydrogen and nitrogen.

English name for the constellation Taurus.

Any sudden emission of unusually strong electromagnetic radiation from a celestial object.

gamma-ray burster, X-ray burster.

A representation in graphical form of the way the latitudes at which sunspots appear vary throughout the solar cycle. It was first plotted in 1922 by E. W. Maunder and is also known as the Maunder diagram. On a graph with solar latitude as the vertical axis and time in years as the horizontal axis, a vertical line covering one degree in latitude is plotted for each sunspot group centred at that latitude within a Carrington rotation. The result is a pattern reminiscent of butterfly wings, which gives the diagram its popular name.

A type of flare star in which there are small regular variations in brightness during the quiet phase between flares. The group is named after its eighth magnitude prototype. BY Draconis stars are red dwarfs, of spectral type K or M. Of those known, a high proportion are definitely in binary systems. The variability, which amounts to no more than a few hundredths of a magnitude in a maximum period of a few days, is thought to be due to a luminous spot on the surface of the rotating star. See also: UV Ceti star.