Fr.: arc circumzénithal
A colorful halo centered on the zenith, appearing when the solar elevation above the horizon is not too high (< 32°).
Fr.: zénith géodésique
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
durâ-ye sarsu, duri-ye ~
Fr.: distance zénithale
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.
teleskop-e sarsu, dvrbin-e ~
Fr.: télescope zénithal
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.
Of or relating to the → zenith; located at or near the zenith.
Fr.: puit zénithal
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.