The symbol normally used for redshift.

symbiotic stars.

Wolf sunspot number.

Abbreviation for zero-age main sequence.

Abbreviation for Zodiacal Catalogue.

The splitting of spectral lines into a number of components when the source is in a magnetic field.

The location of the Special Astrophysical Observatory of the Russian Academy of Sciences.

The overhead point. The astronomical zenith is formally defined as the extension upwards to infinity of a plumb line. The geocentric zenith is the continuation of a line from the centre of the Earth through the observer. The geodetic zenith is the normal to the geodetic ellipsoid or spheroid at the observer’s location.

The angular distance from the zenith of a point on the celestial sphere, measured along a great circle.

A telescope mounted to point vertically in order to make positional measurements on stars passing through and near the zenith.

The hypothetical rate at which meteors of a particular meteor shower would be observed by an experienced observer, watching a clear sky with limiting magnitude 6.5, if the radiant were located in the zenith. The lower the altitude of the radiant, the lower the observed rate. To a first approximation the ratio of the observed rate to the zenithal rate is the sine of the altitude angle of the radiant.

For a population of stars, such as a cluster, formed at the same time, the main sequence on the Hertzsprung-Russell diagram as it would have been at the start of their hydrogen-burning phase.

See also: stellar evolution.

Abbreviation for zenithal hourly rate.

A band around the celestial sphere that is imaginary, which lies approximately 9° to each side of the elliptic the perceived annual path of the Sun, in which the Moon and all the planets apart from Pluto sometimes are found. The imaginary band is used in astrology where 12 different names are given that correspond to 12 constellations found in the band.

zodiacal light.