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

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 line connecting the two apsides, i.e. the major axis of an elliptical orbit. → apsis.

Apsides, pl. of → apside; → line.

The point of greatest or least distance of the orbit of a celestial body from a center of attraction. The closest point is the → periapsis, the further point the → apoapsis.

L. apsis "arch, vault," from Gk. hapsis "loop, arch," from haptein "fasten together".

Mod.Pers. habâk "top of the head; the summit of a mountain".

To think carefully about, especially in order to make a decision; contemplate; reflect on (dictionary.com).

M.E. consideren, from O.Fr. considerer "reflect on, study," from L. considerare "to examine, look at closely," literally "to observe the stars," from → com- "with" + sider (stem of sidus) "star, group of stars," → sideral.

Âgâridan, from intensive prefix â- + gâr-, variants gar-, gâl- "to consider, observe," as in engâridan "to suppose," negaristan "to observe, look, notice," segâl "thought," segâlidan "to think, meditate," ultimately from Proto-Iranian *kar- "to observe, to consider;" cf. Av. kar- "to remember; to impress on memory;" Skt. kal- "to observe, consider," kalayati "considers, observes."

1) Rather large or great in size, distance, extent, etc.
2) Worthy of respect, attention, etc.; important; distinguished (dictionary.com).

→ consider; → -able.

The act or an instance of considering.

→ consider; → -tion.

A rural area; he inhabitants of a countryside.

→ country; → side.

Rustâ, from Mid.Pers. rôstâk, rôtastâk "village, district, river-bed;" loaned into Armenian rotstak, ərotastak "district."

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.

The → sidereal time related to the angle between the → prime meridian and the → mean vernal equinox, measured in the plane of the equator.

→ mean; → Greenwich Meridian; → sidereal; → time.

The number and fraction of → mean sidereal days elapsed on the → Greenwich meridian since 12h January 1, 4773 BC (mean sidereal).

→ Greenwich meridian; → sidereal; → date.

The integral part of the → Greenwich sidereal date.

→ Greenwich; → sidereal; → day; → number.

→ Kennelly-Heaviside layer.

English physicist Oliver Heaviside (1850-1925).

A → chemical element that is → geochemically characterized as having a strong → affinity to partition into → metals relative to → silicates. The highly siderophile elements, → ruthenium (Ru), → rhodium (Rh), → palladium (Pd), → rhenium (Re), → osmium (Os), → iridium (Ir), → platinum (Pt), and → gold (Au), are of interest to planetary scientists because they give insights into the early history of → accretion and → differentiation. HSEs prefer to reside in the metal of planetary cores. Therefore, the HSEs found in planetary → mantles are considered to be overabundant relative to their known preferences for metal over silicate. Therefore, it has been inferred that processes other than → equilibrium partitioning have been responsible for establishing the abundances of → mantle siderophiles. A detailed understanding of the absolute → concentrations and relative abundances of the HSEs may therefore give important insights into the earliest history of a planet (Jones et al., 2003, Chemical Geology 196, 21).

From Gk. sidero-, from sideros "iron" + → -phile.

Âhandust, from âhan, → iron, + -dust, → -phile.

One of several layers in the Earth's ionosphere occurring at 90-150 km above the ground. It reflects medium-frequency radio waves whereby radio waves can be propagated beyond the horizon.

Named after the American electrical engineer Arthur Edwin Kennelly (1861-1939) and the English physicist Oliver Heaviside (1850-1925), who independently predicted the existence of the reflecting layer in 1902; → layer.

Of an elliptical orbit, the straight line drawn from the → perigee to the → apogee.

→ line, → apsides.

Local time measured by the apparent motion of the stars. It is the most useful form of sidereal time since it gives the right ascension of a transiting celestial object at a given location.

→ local; → sidereal; → time.

The Moon's hemisphere which is not visible from the Earth. The Moon always shows the same face to the Earth, because Earth and Moon are → tidally locked. This means that the period of → lunar rotation on it axis is the same as its sidereal revolution period around the Earth (→ sidereal month). In other words, the Moon is in → synchronous rotation with the Earth. As a result, the same side always faces the Earth. To be more precise, taking the lunar → libration into account, the Moon presents about 59% of its surface to Earth. → libration in longitude, → libration in latitude, → physical libration, → geometrical libration.

→ lunar; → far; → side.

Same as → sidereal month.

→ lunar; → sidereal; → orbital; → period.

The average time interval between two successive → upper transits of the → mean equinox.

→ mean; → sidereal; → day.