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

The excess of the equatorial diameter over the polar diameter of a celestial object, such as the Earth or the Moon.

→ equatorial; bulge, from O.Fr. bouge "leather bag," from L. bulga "leather bag," of Gaulish origin.

Barâmadegi, from barâmadan "to grow out; to emerge," from bar- "on, upon, up" (Mid.Pers. abar, O.Pers. upariy "above; over, upon, according to," Av. upairi "above, over," upairi.zəma- "located above the earth;" cf. Gk. hyper- "over, above;" L. super-; O.H.G. ubir "over;" PIE base *uper "over") + âmadan "to come" (Mid.Pers. âmadan; O.Pers. gam- "to come; to go;" Av. gam- "to come; to go," jamaiti "goes;" cf. Skt. gamati "goes;" Gk. bainein "to go, walk, step;" L. venire "to come;" Tocharian A käm- "to come;" O.H.G. queman "to come;" E. come; PIE root *gwem- "to go, come").

An astronomical → coordinate system for indicating the positions of → celestial objects on the → celestial sphere. The system consists of two components, → right ascension and → declination. Right ascension is the angle between the → vernal equinox and the point where the → hour circle intersects the → celestial equator. The right ascension is always measured eastward from the vernal equinox, in the units of hours, minutes, and seconds. Declination is the angle between the celestial equator and the position of the star measured along the star's hour circle. It is measured in degrees, minutes, and seconds north or south of the celestial equator. By definition, the vernal equinox is located at right ascension 0h and declination 0°. Equatorial coordinates change with time due to the → precession of the Earth's → rotation axis.

→ equatorial; → coordinate; → system.

Celestial coordinates in the → equator system.

→ equatorial, → coordinate.

A telescope mounting consisting of a polar axis pointed toward the celestial pole, and a declination axis supporting the instrument at right angles to the polar axis.

→ equatorial; → mounting.

The plane containing a celestial object's equator.

→ equatorial; → plane.

Of a planet, the distance from the center to the equator. For Earth it is 6,378.1370 km. Jupiter has an equatorial radius 11.2 times Earth's value.

→ equatorial; → radius.

A slow, dense → stellar wind (high → mass loss rate) emanating from equatorial regions of a → B[e] star. The equatorial and → polar winds are the two main wind components in B[e] stars. The mechanism suggested to explain this wind morphology is the rotationally induced → bistability mechanism.

→ equatorial; → wind.

A prefix meaning "equal," as in → equinox, → equilibrium, → equipartition.

M.E., from L. aequi-, combining form representing aequus, → equal.

Hamug-, → equal.

Math.: having three axes of the same length. Also equiaxed.
Physics: A crystal exhibiting similar dimensions in all directions.

→ equi-; → axis.

A triangle having three equal sides.

→ equi-, → lateral, → triangle.

Sé-pahlu-barâbar, from sé, → three, pahlu, → side, barâbar, → equal.

A state of balance or rest between the forces operating on or within a physical system. → stable equilibrium; → unstable equilibrium; → dynamical equilibrium.

From L. æquilibrium, from æquus, → equal + libra "a balance, scale."

Tarâzmandi, noun of tarâzmand "in equilibrium," from tarâz "level; a level" + possession suffix -mand. The first component from tarâzu "balance, scales," Mid.Pers. tarâzên-, taraênidan "to weigh;" Proto-Iranian *tarāz-, from *tarā- "balance, scale" (cf. Skt. tulā- "scales, balance, weight," from tul- "to weigh, make equal in weight, equal," tolayati "weighs, balances;" L. tollere "to raise;" Gk. talanton "balance, weight," Atlas "the Bearer" of Heaven;" Lith. tiltas "bridge;" PIE base telə- "to lift, weigh") + Av. az- "to convey, conduct, drive," azaiti drives" (cf. Skt. aj- "to dive, sling," ájati "drives," ajirá- "agile, quick;" Gk. agein "to lead, guide, drive, carry off;" L. agere "to do, set in motion, drive," from PIE root *ag- "to drive, move," → act).

A concept whereby chemical → concentrations among geological or environmental media are at equilibrium, and therefore the partitioning of metals in those media can be predicted based on → partition ratios.

→ equilibrium; → partitioning.

The position of an oscillating body at which no net force acts on it.

→ equilibrium; → position.

A state in which a → thermodynamic system is in → thermodynamic equilibrium.

→ equilibrium; → state.

The date on which the day and night have exactly the same length. Contrary to the widespread statement, the day and night are not equal at the → equinox. The higher the → latitude, the greater the difference. In fact the day and night lengths are equal at the equinox only if the strict theoretical definition is used, according to which sunset and sunrise are the moments when the center of the Sun crosses the → horizon. There are two reasons for this inequality: 1) The Sun is a disk, not a point source. It is about 30 arc minute wide, hence sunrise corresponds to the moment the top of the disk (and not its center) emerges out of the horizon. Similarly, sunset is when the last part of the disk sinks below the horizon. The Sun takes about a minute to move from its center to its edge (the Earth rotates about 1 degree in 4 minutes). This sums to two minutes (a minute for sunset and a minute for sunrise) that adds to 4 minutes in the total difference. 2) The atmosphere acts as a lens, and slightly bends the Sun's rays because of the → atmospheric refraction. When we look at the setting Sun, the fact is that it was already set. Unlike the equinox, which is a fixed date all-over the globe, the date of the equilux is dependent upon the → latitude of the observer. Between the poles and about 20 degrees latitude, it is generally a few days before the → vernal equinox or a few days after the → autumnal equinox .

→ equi-; → lux.

Of or relating to an equinox or to the equality of day and night.

Adjective of → equinox.

The great circle of the celestial sphere through the celestial poles and equinoxes; the hour circle of the vernal equinox. → colure.

→ equinoctial; → colure.

One of the two points of intersection of the ecliptic and the celestial equator. Same as equinox.

→ equinoctial; → point.

1) One of the two points on the → celestial sphere where the → celestial equator intersects the → ecliptic, that is when the apparent → ecliptic longitude of the Sun is 0° or 180°.
2) Either of the times at which the center of the Sun's disk passes through these points. → autumnal equinox; → vernal equinox.
At equinox, the length of the day and the night are equal all over the globe. The equinox is not a fixed point; it moves due to → precession and → nutation. If only precession is considered, we deal with the → mean equinox of date. If nutation is also taken into account, then we are concerned with the → true equinox.

M.E., from O.Fr. équinoxe, from M.L. equinoxium "equality of night (and day)," from L. æquinoctium, from æquus, "→ equal" + nox "→ night" (gen. noctis). In Gk. isimeria "equal day," from isos "equal," → iso-, + hemera "day."

From hamug, → equal, + -ân suffix denoting time and place.

1) General: Equal sharing of the → total energy among all → components of a → system.
2) In the → kinetic theory of gases, the → theorem according to which → molecules in → thermal equilibrium have the same average energy (¹/₂ kT) associated with each independent → degree of freedom of their motion.

→ equi-; → partition.