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

A colorful halo centered on the zenith, appearing when the solar elevation above the horizon is not too high (< 32°).

→ circum-; → zenithal; → arc.

The intersection of the prolongation of the outward → normal to the → reference ellipsoid at the point in question with the → celestial sphere.

→ geodetic; → zenith.

The point on the celestial sphere directly above the observer's head, opposite to the direction in which gravity acts. Opposite of → nadir.

M.E. cenith, from O.Fr. cenith, from M.L. cenit, senit, incorrect transliteration of Ar. samt (سمت) "path, direction," abbreviation of samt ar-ras (سمت‌الرأس), literally "road above one's head."

Sarsu, literally "the way over the head," from sar→ head + su, → direction.

The angular distance of a celestial body from the zenith. The zenith distance is 90° minus the body's altitude above the horizon (i.e. the complement of the altitude) and hence is also known as coaltitude.

→ zenith; → distance

The number of → meteors expected to be seen under ideal conditions if the → radiant of the → meteoroid stream is at the → zenith of the → observer.

→ zenith; → hour; → rate.

A → telescope that is mounted on a → vertical axis or moves only a small amount from the vertical. It is primarily used to determine positional measurement of stars moving near the → zenith. The advantage is that there is no → atmospheric refraction occurring at the zenith. If a star on one night passes through the center of eyepiece, one must observe it six month later, and see if the star has been offset by the center. A shift would mean a measure of parallax. See also: → zenithal well.

→ zenith; → telescope

Of or relating to the → zenith; located at or near the zenith.

→ zenith; → -al.

1) A well used in Antiquity from bottom of which the sky could be observed during the day with a better contrast. The aperture of the well reduced the light diffused by the sky.
2) A vertical tunnel in → Paris Observatory (built in 1667), from the top roof to the underground vaults, 55m deep. This well had the purpose of observing the stars near the → zenith and measure their → parallaxes resulting from the Earth motion around Sun. A long plumb line was attached to the top of the well. Astronomers thought they could measure the stellar shifts with respect to the plumb line. The problem was, however, the lack of stability of the images, because the well acted in fact as a chimney generating turbulence. So that the zenithal well was hardly used. See also: → zenith telescope.

→ zenithal; → well.