Vernal equinox. Also called FIRST POINT OF ARIES


Related Terms

AIR ALMANAC

1. A periodical publication of astronomical data designed primarily for air navigation, but often used in marine navigation. 2. A joint publication of the U.S. Naval Observatory and H. M. Nautical Almanac Office, Royal Greenwich Observatory, designed primarily for air navigation. In general the information is similar to that of the Nautical Almanac, but is given to a precision of 1' of arc and 1s of time, at intervals of 10m (values for the sun and Aries are given to a precision of 0.1').

S.H.A.

Sideral hour angle the angular distance between the GHA of Aries and the GHA of a star (measured in a westward direction).

SHA

Sideral hour angle the angular distance between the GHA of Aries and the GHA of a star (measured in a westward direction).

LONGITUDE OF THE ASCENDING NODE

1. The angular distance in the ecliptic from the vernal equinox to the ascending node of the orbit. 2. The angular distance, always measured eastward, in the plane of the celestial equator from Greenwich through 360°.

CELESTIAL LONGITUDE

Angular distance east of the vernal equinox, along the ecliptic; the arc of the ecliptic or the angle at the ecliptic pole between the circle of latitude of the vernal equinox at the circle of latitude of

LOCAL SIDEREAL NOON

Zero hours local sidereal time, or the instant the vernal equinox is over the upper branch of the local meridian. Local sidereal noon at the Greenwich meridian is called Greenwich sidereal noon.

LONGITUDE OF THE MOON’S NODES

The angular distance along the ecliptic of the moon’s nodes from the vernal equinox; the nodes have a retro- grade motion, and complete a cycle of 360° in approximately 19 years.

VERNAL

Pertaining to spring. The corresponding adjectives for summer, fall, and winter are aestival, autumnal, and hibernal.

EQUINOCTIAL COLURE

The great circle of the celestial sphere through the celestial poles and the equinoxes; the hour circle of the vernal equinox

GREENWICH SIDEREAL NOON

Local sidereal noon at the Greenwich meridian; zero hours Greenwich sidereal time, or the instant the vernal equinox is over the upper branch of the Greenwich meridian.

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