An Etymological Dictionary of Astronomy and Astrophysics
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The → Greenwich Mean Sidereal Time corrected for → nutation. Therefore, it is measured with respect to the → true vernal equinox. GAST and GMST differ by the → equation of the equinoxes.

→ Greenwich Meridian; → apparent; → sidereal; → time.

The → sidereal time related to the angle between the → prime meridian and the → mean vernal equinox, measured in the plane of the equator.

→ mean; → Greenwich Meridian; → sidereal; → time.

The → prime meridian that separates east from west in the same way that the Equator separates north from south. It is defined by the position of the → Airy transit circle.

A borough in southeast London, England, on the Thames River. It is the site of the original Royal Observatory, through which passes the prime meridian, or longitude 0°; → meridian.

The number and fraction of → mean sidereal days elapsed on the → Greenwich meridian since 12h January 1, 4773 BC (mean sidereal).

→ Greenwich meridian; → sidereal; → date.

The integral part of the → Greenwich sidereal date.

→ Greenwich; → sidereal; → day; → number.