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

Of or relating to the sky or visible heavens.

M.E., from O.Fr., from M.L. celestialis, from L. cælestis "heavenly," from cælum "heaven, sky."

Âsmâni related to âsmân, → sky.

The Earth's axis extended to the → celestial pole.

→ celestial; → axis.

→ astronomical object.

→ celestial; → body.

Any system of coordinates used to define a point on the celestial sphere (zenith distance, altitude, celestial latitude, celestial longitude, etc.).

→ celestial; → coordinates.

An imaginary great circle on the sky half-way between the → celestial poles. It is the projection of the → equator of the Earth on the sky.

→ celestial; → equator.

A small globe representing the celestial sphere, on which the apparent positions of the stars are indicated.

→ celestial; → globe.

A great circle on the → celestial sphere having a plane that passes through the center of the Earth at a right angle to the line formed by an observer's → zenith and → nadir.

→ celestial; → horizon.

Angular distance → north or → south measured from the → ecliptic to a → celestial object.

→ celestial; → latitude.

Angular distance to an object measured eastward along the → ecliptic from the → vernal equinox.

→ celestial; → longitude.

Derežnâ, → longitude; âsmâni→ celestial.

The branch of astronomy that deals with the calculation of motions of celestial bodies under the action of their mutual gravitational attractions.

→ celestial; → mechanics.

Mekânik, → mechanics; âsmâni, → celestial.

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

→ celestial; → meridian.

→ astronomical object.

→ celestial; → object.

The point of the sky, north or south, where the projection of the Earth's axis of rotation intersects the → celestial sphere. They are at 90° relative to the → celestial equator. Because of → precession, the celestial poles describe a circle around the ecliptic's poles every 25,800 years.

→ celestial; → pole.

An imaginary sphere, of large but indefinite dimension, used as a basis to define the position coordinates of celestial bodies. The center can be the Earth, the observer, or any other point which plays the role of origin for a given system of coordinates. Seen from the Earth, the celestial sphere rotates around the → celestial axis every 23h 56m 04s (the → sidereal day), as a result of the Earth's rotation. Two important circles on the celestial sphere are the → celestial equator and the → ecliptic. The angle between them, about 23.40 degrees, is known as the → obliquity of the ecliptic. The celestial equator and the ecliptic intersect at two points, → vernal equinox and → autumnal equinox. The positions of the → celestial poles and therefore that of the → celestial equator move gradually on the celestial sphere, due to → precession.

→ celestial; → sphere.

The point in the → northern hemisphere where the → rotation axis of Earth touches the → celestial sphere. The star → Polaris, also called the Pole Star, is located very near this point, at an angular separation of 42 degrees (about 1.4 lunar diameters).

→ north; → celestial; → pole.

The point in the → southern hemisphere where the → rotation axis of the Earth touches the → celestial sphere. In contrast to the → north celestial pole, no bright star is visible in that direction.

→ north; → celestial; → pole.

The → celestial equator of date, which is the → great circle on the → celestial sphere perpendicular to the instantaneous axis of rotation of the Earth. Its interaction with the → ecliptic defines the → vernal equinox of date and the → autumnal equinox of date.

→ true; → celestial; → equator.

The direction of the Earth's instantaneous rotation pole. It differs from the pole due to the short time-scale (days or decades) variations called → nutation.

→ true; → celestial; → pole.