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

→ annual motion.

→ annual; → apparent; → motion.

General: Open to view, visible; appearing as actual to the eye or mind.
In astronomy, observed.

O.Fr. aparant, from L. apparentem, pr.p. of apparere "to appear," from ad- "to" + perere "to come forth, be visible".

Padidâr "appearing, manifest," from padid "in sight, evident, clear," from Mid.Pers. patdit, from O.Pers./Av. patiy-/paiti "toward, against, back" (cp. Skt. prati- "near, toward, against, in return," Gk. proti, pros "face to face with, toward, in addition to") + O.Pers./Av. di-/dâ(y)- "to see" (Skt. dhi- "to think"), Mod.Pers. didan "to see".

The angular diameter of a celestial body expressed in degrees, minutes, and seconds of arc, or in radians.

→ apparent; → diameter.

The angular distance between two celestial bodies (e.g. the components of a binary star system), expressed in degrees, minutes and seconds of arc.

→ apparent; → distance.

The angular diameter of the circle of light that the eye sees through an eyepiece.

→ apparent; → field.

The circle determined by the intersection of the heavens with a → cone whose → vertex is the → eye, and whose elements are tangent to lines of the Earth's surface. Same as → visible horizon. Assuming that there is no → atmospheric refraction, apparent horizon coincides with → geometric horizon. See also → sea horizon.

→ apparent; → horizon.

A measure of a star's observed brightness (opposed to → absolute magnitude); symbol m. It depends on the star's → intrinsic brightness, its distance from the observer, and the amount of → interstellar absorption. The brightest star → Sirius has an apparent magnitude of -1.46, while the weakest stars visible with the naked eye in the most favorable observation conditions have magnitudes of about +6.5. The stars of magnitudes less than +23 are measured by professional observatories, whereas those of magnitudes less than +30 by a telescope such as the → Hubble Space Telescope (M.S.: SDE).

→ apparent; → magnitude.

The moment when the center of the Sun crosses the meridian. Same as true noon.

→ apparent; → noon.

Same as → apparent position.

→ apparent; → place.

1) The position on the celestial sphere at which a heavenly body would be seen from the Earth at a particular time.
2) A position given by the coordinates calculated for a star, if it were seen from the Earth's centre, relative to the → real equator and the → real equinox, at a certain date. It includes the displacements from one heliocentric direction, given in a stellar catalogue, due to → precession, → nutation, → aberration, → proper motions, → annual parallax, and light gravitational deviation (M.S.: SDE).

→ apparent; → position.

The instant of time when the object is in the East and the geometric → zenith distance is equal to 90° plus the → horizontal refraction plus the semidiameter minus the → parallax.

→ apparent; → rising.

The instant of time when the object is in the West and the geometric → zenith distance is equal to 90° plus the → horizontal refraction plus the semidiameter minus the → parallax.

→ apparent; → setting.

The time interval between two successive → upper transits of the → true equinox of date.

→ apparent; → sidereal; → day.

The → mean sidereal time corrected for the → nutation and shift in the obliquity of the ecliptic that occurs as a result of the Moon's gravitational effect. Apparent sidereal time differs from mean sidereal time in that the → true vernal equinox point is used.

→ apparent; → sidereal; → time.

The duration of one rotation of the Earth on its axis (→ Earth's rotation), with respect to the → apparent Sun. It is measured by successive transits of the apparent Sun over the lower branch of a → meridian.

→ apparent; → solar day.

The time based on the motion of the → apparent Sun and kept by dividing the day into 24 equal hours.

→ apparent; → solar; → time.

The → true Sun as seen by an observer on Earth. The term "apparent Sun" is used in contrast to → mean Sun, which refers to an average of the Sun's position). See also: → apparent solar time and → mean solar time.

→ apparent; → Sun.

→ Apparent magnitude in the visual wavelengths, around 5600 Å. → visual magnitude.

→ apparent; → visual; → magnitude.

Judging from what is apparent. As far as one knows or can see.

→ apparent; → -ly.

The → Greenwich Mean Sidereal Time corrected for → nutation. Therefore, it is measured with respect to the → true vernal equinox. GAST and GMST differ by the → equation of the equinoxes.

→ Greenwich Meridian; → apparent; → sidereal; → time.