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

The part of the arm between the → elbow and the → wrist.

From fore- a prefix meaning "before; front; superior," related to → per-; → arm.

Araš, variant ârenj "elbow;" Mid.Pers. âranj; O.Pers. arašan- "cubit;" Av. arəθnâ- "elbow;" Skt. aratni- "elbow," Iranian stem aratan-, araθn-, borrowed from Iranian into General Slavic as aršin "ell."

The time taken for the Sun to revolve once around the center of the Milky Way, amounting to about 220 million years.

→ galactic; → year.

1) A hollow muscular organ that pumps the blood through the circulatory system by rhythmic contraction and dilation. In vertebrates there may be up to four chambers (as in humans), with two atria and two ventricles.
2) The heart regarded as the centre of a person's thoughts and emotions, especially love or compassion (OxfordDictionaries.com).

M.E. herte, from O.E. heorte "heart breast, soul, spirit, will, desire; courage; mind, intellect;" cf. O.Saxon herta, O.Frisian herte, O.Norse hjarta, Du. hart, O.H.G. herza, Ger. Herz; cognate with Pers. del, as below; PIE root *kerd- "heart."

Del "heart" (Pashtu z'rrah, zyah; Baluci zirde "heart, mind, soul;" Kurd. zar; Sogd. žyâwar); Mid.Pers. dil; Av. zərəd-; cf. Skt. hrd-; Gk. kardia; L. cor "heart" (Fr. cœur; Sp. corazon, It. cuore); Russ. serdtse; Arm. sirt; E. heart, as above.

A high-precision echelle spectrograph built for exoplanet findings and installed on the ESO's 3.6m telescope at La Silla Observatory in Chile. The first light was achieved in February 2003. HARPS has discovered dozens of exoplanets, making it the most successful planet finder behind the Kepler space observatory. HARPS can detect movements as small as 0.97 m s^-1 (3.5 km h^-1), with an effective precision of the order of 30 cm s^-1, and a → resolving power of 120,000 (Mayor et al., 2003, ESO Messengar 114, 20).

→ high; → accuracy; → radial; → velocity; → planet; → search; → -er.

A → linear differential equation if the right-hand member is zero, Q(x) = 0, on interval I.

→ homogeneous; → linear; → differential; → equation.

A molecule that is composed of only one type of → chemical element, e.g. the → molecular hydrogen and → ozone.

→ homo-; → nuclear; → molecule.

→ obliquity of the ecliptic.

→ inclination; → Earth; → equator.

A → near-Earth object whose → orbit lies always inside Earth's orbit.

→ inner; → Earth; → object.

A period of 365.25 days adopted in the Julian calendar for the length of the year.

→ Julian calendar; &rarr ;year.

Shearing motion of an ensemble of particles, each on a nearly circular, → Keplerian orbit. → Orbital velocity decreases as orbital radius increases, yielding shear. Viscous drag on such shear, due to ring-particle collisions, plays a key role in ring processes (Ellis et al., 2007, Planetary Ring Systems, Springer).

→ Keplerian; → shear.

In solar calendars the year that contains 366 days, instead of 365, in order to keep the calendar in pace with the real solar time.

→ leap; → year.

The three criteria that identify → leap years in the → Gregorian calendar: 1) The year must be evenly divisible by 4; 2) If the year can be evenly divided by 100, it is not a leap year, unless; 3) The year is also evenly divisible by 400. This means that in the Gregorian calendar, the years 1600, 2000, and 2400 are leap years, while 1700, 1800, 1900, 2100, 2200, 2300 and 2500 are not leap years.

→ leap; → year; → rule.

→ light-year

→ light; → year.

The distance that light travels in one year at about 300,000 km per second, i.e. 9.5 x 10¹² km. It is equal to about 63,000 → astronomical units. See also → parsec.

→ light; → year.

Confined to first-degree algebraic terms in the relevant variables.

Adj. of → line.

The rate of change of the → linear velocity with time. It is defined by the expression Δv/Δt and is equal to the → first derivative of the → linear velocity.

→ linear; → acceleration.

Taking the first term in the Taylor series as an approximation to a mathematical function at a given point. → first approximation.

→ linear; → approximation.

A version of → planispheric astrolabe in which the → celestial sphere and the various circles of altitude and declination are projected on to a line represented by a staff. The staff is equivalent to the meridian line and contains markings to indicate the centers of these circles and their intersections with the meridian. By attaching three ropes to the appropriate points on the staff to act as radii, the circles and their intersections can be reconstructed. One of the ropes was attached to a plumb line. A scale giving chord lengths in the meridian circle extended the linear astrolabe's range of applications. It was invented by the Iranian mathematician and astronomer Sharafeddin Tusi (c1135-1213), but no early example has survived. Same as → Sharafeddin's staff and Tusi's staff.

→ linear; → astrolabe.

A measure of how well data points fit a straight line. When all the points fall on the line it is called a perfect correlation. When the points are scattered all over the graph there is no correlation.

→ linear; → correlation.

The real physical diameter, as opposed to angular diameter.

→ linear; → diameter.