An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

The great circle on the → celestial sphere, passing through the two → celestial poles and the observer's → zenith.

→ celestial; → meridian.

A fictitious meridian that rotates independently of the Earth at the uniform rate implicitly defined by → Terrestrial Dynamical Time (TDT).

→ ephemeris; → meridian.

The → ellipse through the point in question which passes through the → geodetic poles.

→ geodetic; → meridian.

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 meridian through any particular place, serving as the reference for local time, in contrast to the Greenwich meridian.

→ local; → meridian.

A meridian passing through the Earth's → magnetic poles.

→ magnetic; → meridian.

1) Geography: An imaginary line on the Earth's surface joining the north and south poles at right angles to the equator. See also → local meridian, → prime meridian.
2) Astron.: An imaginary great circle on the → celestial sphere that passes through its poles and the observer's → zenith.

M.E., from O.Fr. meridien, from L. meridianus "of noon, southern," from meridies "noon, south," from meridie "at noon," altered by dissimilation from *medi die, locative of medius "mid-" + dies "day."

Nimruzân, coined by Pers. astronomer (A.D. 973-1048) in his at-Tafhim, from nim "mid-, half" (Mid.Pers. nêm, nêmag "half;" Av. naēma- "half;" cf. Skt. néma- "half") + ruz, → day, + -ân suffix denoting time and place.

Same as hour angle.

→ meridian; → angle.

A telescope with a graduated vertical scale, used to measure the declinations of heavenly bodies and sometimes to determine the time of meridian transits.

→ meridian; → circle.

An instrument designed to observe objects when they cross the meridian.

→ meridian; → observation.

The observation of a star when it crosses an observer's meridian.

→ meridian; → observation.

The moment when a celestial object crosses an observer's meridian. Same as meridian transit.

→ meridian; → passage.

The line connecting the Moon's north pole with its south pole, and passing through the center of the lunar disk. The longitude of the Moon's prime meridian is zero degrees.

→ Moon; → prime meridian.

The meridian at which longitude is defined to be 0°. The meridian running through Greenwich.

→ primary; → meridian.