A rare type of asteroid, interpreted as being similar to the class of meteorites known as chondrites. Only Apollo and a few other Earth-approaching asteroids are known to belong to this class.

Abbreviation for quasi-stellar object. quasar.

An instrument for measuring the altitudes of stars and the angular separation between celestial objects, consisting of a graduated quarter-circle and a movable sighting arm. Prior to the invention of the telescope, such instruments were the only ones available to astronomers for positional measurements. Tycho Brahe 1546-1601, for example, used a large mural quadrant, built on to a specially constructed wall lying along the north-south direction. On instruments made after the invention of the telescope, telescopic sights were often employed. The modern equivalent is the transit circle.

An annual meteor shower, the radiant of which lies in the constellation Boötes, near the border with Hercules and Draco. The name dates from the time when this area of sky was identified as the constellation Quadrans Muralis, now no longer used. The peak of the shower occurs on about 3 January and the normal limits are 1-6 January. The narrow stream of meteors is not associated with any known comet, and the shower is somewhat variable, peak rates occurring over a relatively short time period.

The position of the Moon or of a planet when its angular distance from the Sun, as viewed from the Earth, is 90°.

A theory, not yet developed, that aims to unite Grand Unified Theories and a theory of the gravitational interaction into a single unified theory in which all interactions in physics are described by a unified set of equations. If achieved, it would unify General Relativity and quantum theory. In a rigorous form, the theory would describe conditions in the universe about 10 to the power of -43 seconds after the onset of the Big Bang.

Originally the days of the solstices and equinoxes, dividing the year into four quarters. In the English legal system, the quarter days for collecting rents, and so on are: 24 June, 26 September, 25 December and 25 March.

A small extragalactic object that is exceedingly luminous for its angular size and has a high redshift. The word originated as a contraction of quasi-stellar radio source, the term given in 1963 to a class of apparently star-like objects, emitting radio waves and having high redshifts. Quasars are now generally believed to be the most luminous type of active galactic nuclei. Around a small number, the faint nebulous light of a surrounding galaxy has been detected. Many thousands of quasars have been catalogued. In general, quasars have a spectrum that shows emission lines, high redshifts typically from 0.5 to 4, although VALUES (higher and lower than these have been recorded, and they are so compact that they appear as sharp as stars on photographs. Although the quasars discovered in the 1960s were all radio sources, most of those now known are not strong radio sources. Quasars have the largest redshifts found, and their importance in astronomy stems primarily from this feature. If the redshifts follow from the expansion of the universe, Hubble’s law can be applied. It follows that they are the most distant objects observable, some of them more than 10 billion light years from our Galaxy. The light from quasars has reached us from long ago, so in principle it can tell us about the state of the universe billions of years in the past. The light from distant quasars shows the Lyman-alpha forest of numerous absorption lines of hydrogen at a variety of lower redshifts. This absorption occurs in hydrogen clouds near the quasar. If the light from a distant quasar passes through an intervening galaxy, a gravitational lens effect may be seen. The fact that we see such remote objects means that they are intrinsically very luminous, from a few to a hundred times the luminosity of a normal galaxy. The presence of emission lines implies that energy is generated through non-thermal mechanisms. Very-long-baseline interferometry shows that the central energy source in quasars is confined to a volume of space similar to the size of the solar system. This implies that the energy source is probably the infall of matter to a supermassive black hole.

quasar.

quasar.

Asteroid 1915, diameter 0.4 km, discovered in 1953 when it made a close approach to the Earth. It is a member of the Amor group.

The Sun when it is at the minimum level of activity in the solar cycle, with little evidence of solar activity.