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

A person, usually an official, who is in charge of the records, correspondence, minutes of meetings, and related affairs of an organization, company, association, etc. (Dictionary.com).

M.E. secretarie "one trusted with private or secret matters; confidant," from M.L. secretarius "confidential officer, confidant, clerk, notary," from L. secretum "a secret, a hidden thing."

Dabir, from Mid.Pers. dipîr, contraction of dipîvar (Mid.Pers. dip, dīp "document;" dīb "letter"); from O.Pers., from Proto-Ir. *dipī-uara- "he who preserves the documents;" cf. O.Pers. dipī- "inscription" + *Huar- "to cover;" cf. Av. vār- "to cover, hide, protect."

The head or chief administrative officer of a secretariat.

→ secretary; → general.

1) Free from or not exposed to danger or harm; safe.
2) To get hold or possession of; procure; obtain.

From L. securus "free from care, quiet, easy," also "careless, reckless;" of things, "free from danger, safe," from *se cura, from se "without, free from," + cura, → care.

Zilé, from Tabari zil, zilé "firm, fixed," zil hâkerdan "to fix, fasten," of unknown origin.

To separate or set apart from others or from the main body or group; isolate.

From M.E. segregat, from L. segregatus, p.p. of segregare "separate from the flock, isolate, divide," from se- "apart from" + greg-, ablative of grex, gregis "herd, flock, crowd," cf. Gk. gergera "swarm, flock;" maybe related to Old Khotanese -gris- in hamgris- "to assemble."

Savâyidan, from savâ "separate, apart;" probably related to Mid.Pers. s'w- "to crush," sây- "to rub, wear, tear;" cf. Kurd. (Hawramân) sawa, Roshani sêw-/sêwt, Bartangi siw-/siwd, Yazghulani saw-/sed, Bajui sâw-/sâwd "to rub, smear, grind" (Cheung 2007); Mod.Pers. sây-/sudan "to rub, wear, tear, grind, dissolve;" cf. Skt. śā- "to sharpen, whet."

The act or practice of segregating. The state or condition of being segregated. → mass segregation.

Verbal noun of → segregate.

The → state or → condition of being aware of one's own → personality or → individuality.

→ self-; → awareness.

Half the → latus rectum. For an ellipse, semilatus rectum has the expression l = b²/a, where a and b are semi-major and minor axes of the ellipse. It can also be expressed in terms of → eccentricity, e, as: l = a(1 - e²).

→ semi-; → latus rectum.

A type of giant or supergiant pulsating variable star, with intermediate or late spectra, showing noticeable periodicity in its light changes, accompanied or sometimes interrupted by various irregularities. Periods lie in the range from 20 to more than 2000 days, while the shapes of the light curve may be rather different and variable with each cycle. The amplitudes may be from several hundredths to several magnitudes (usually 1-2 magnitudes in the V filter). Examples are Betelgeuse, Antares, and Rasalgethi. Semiregular variables are classified in several subtypes: SRA, SRB, SRC, and SRD.

→ semi-; → regular; → variable.

Same as → sampling theorem.

→ Shannon entropy; → sampling; → theorem.

1a) The full or proper portion or part allotted or belonging to or contributed or owed by an individual or group.
1b) One of the equal fractional parts into which the capital stock of a joint-stock company or a corporation is divided.
2a) To divide and distribute in shares; apportion.
2b) To use, participate in, enjoy, receive, etc., jointly (Dictionary.com).

M.E., from O.E. scearu "a cutting, shearing; a part or division," related to sceran "to cut;" O.H.G. scara "troop, share of forced labor," Ger. Schar "troop, band," properly "a part of an army," O.N. skör "rim;" from PIE root *(s)ker- "to cut."

Bâš, from Kurd. (Sorani) baš "share, part;" variant of baxš "share, portion;" baxšidan "to divide," → division; bâž "tribute, toll, impost," → distribute.

A burst of very bright → ultraviolet or → soft X-ray radiation expected to occur in → core-collapse supernovae at the instant when the → supernova shock breaks out of the stellar surface. During the collapse of the progenitor → massive star, the density in the iron core increases drastically. Once the core material reaches → nuclear density, the core rebounds generating a → shock wave that moves outward through the star. When the shock reaches the outermost layers, it ejects them out into space at → relativistic speeds.

→ shock; breakout "a forceful escape from being confined or restrained," from break, from M.E. breken, O.E. brecan (cf. Du. breken, O.H.G. brehhan, Ger. brechen), from PIE base *bhreg- "to break" (see also → fraction) + → out.

Borunzani "emergence, evasion," from borun, → out, + zani verbal noun of zadan "to strike, beat," from Mid.Pers. zatan, žatan; O.Pers./Av. jan-, gan- "to strike, hit, smite, kill" (jantar- "smiter"); cf. Skt. han- "to strike, beat" (hantar- "smiter, killer"); Gk. theinein "to strike;" L. fendere "to strike, push;" Gmc. *gundjo "war, battle;" PIE *g^when- "to strike, kill."

Of, relating to, or determined by or from stars.

From M.Fr. sidereal, from L. sidereus "starry, astral," from sidus (genitive sideris) "star, constellation."

Axtari, pertaining to axtar "star," probably a variant of setâré→ star.

The period of → Earth's rotation around its axis, the mean value of which is about 23h 56m 04.092s (23.934 470 hours). In other words, the interval between two successive passages of a star across a given → meridian. The sidereal day is 3 minutes 56 seconds shorter than the → mean solar day. The reason is that Earth moves a little less than a degree around the Sun during the time it takes for one full axial rotation. So, for the Sun to appear on the same meridian in the sky again after one full axial rotation, the Earth has to rotate one extra degree to bring the Sun into the same apparent meridian in the sky. This is also why the stars rise and set about 4 min earlier each day.

→ sidereal; → day.

The angle on the celestial sphere measured westward from the hour circle of the vernal equinox to that of the celestial body.

→ sidereal; → hour angle.

The time taken by the Moon to complete one → revolution around the Earth with respect to a background, → fixed star. The average time is 27.321 661 days (27d 7h 43m 11.5s). Same as → lunar sidereal orbital period.

→ sidereal; → month.

→ sidereal revolution period; → sidereal rotation period.

→ sidereal; → period.

The time taken by a planet or satellite to complete one revolution about its primary with respect to stars. For Earth, same as → sidereal year. Sidereal periods of the solar system planets, interms of the sidereal year, are as follows: Mercury 0.240846 (87.9691 days); Venus 0.615 (225 days); Earth 1 (365.25636 solar days); Mars 1.881; Jupiter 11.86; Satrurn 29.46; Uranus 84.01; and Neptune 164.8. That of the Moon is 0.0748 (27.32 days) and for → Sedna 12050.

→ sidereal; → revolution; → period.

The rotation period of a celestial body with respect to fixed stars. For Earth, same as → sidereal day.

→ sidereal; → rotation; → period.

The time based upon → Earth's rotation with respect to the stars, with the → sidereal day as the unit of measurement. At the moment when the → vernal equinox crosses the → meridian in → upper culmination, sidereal time is equal to zero hours for that observing position. The → hour angle of the vernal equinox is equal to sidereal time.

→ sidereal; → time.

The interval between two successive passages of the Sun, in its apparent → annual motion around the → celestial sphere, through a particular point relative to stars. It is equal to 365.256356 days for the J2000.0 epoch and is 20m 24.5s longer than the → tropical year.

→ sidereal; → year.