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

A comet with orbital period of more than 200 years. → short-period comet; → periodic comet.

→ long; → period; → comet.

A type of → variable star in which variations in brightness occur over long time-scales of months or years. The term generally refers to → Mira variable types.

→ long; → period; → variable.

The angular distance on the Earth's surface, measured east or west from the prime meridian at Greenwich to the meridian passing through a position, expressed in degrees (or hours), minutes, and seconds.

L. longitudo "length," from longus "long," cognate with Pers. derâz, as below, Gk. dolikhos "elongated;" O.H.G., Ger. lang, O.N. langr, M.Du. lanc, Goth. laggs "long;" PIE base *dlonghos- "long."

Derežnâ, from derež (Kurdi, Laki), variants darg "length; long, tall" (Zâzâ), darγ (Ossetic), derâz "long" + -nâ noun forming suffix from adjective, as in derâznâ, pah(n)nâ, farâxnâ, tangnâ, tiznâ. The first element from Mid.Pers. drâz "long;" O.Pers. darga- "long;" Av. darəga-, darəγa- "long," drājištəm "longest;" cf. Skt. dirghá- "long (in space and time);" PIE *dlonghos- "long," as above.

One of the → orbital elements used to specify the orbit of an object in space. It is the angle from the reference direction, called the origin of longitude, to the direction of the → ascending node, measured in the reference plane.

→ longitude; → ascending node.

Of or pertaining to longitude or length. Extending in the direction of the length.

Adj. of → longitude.

1) A → magnetic field whose lines of force (→ line of force) run parallel to the long axis of the → magnet. Longitudinal magnetization of a component can be accomplished using the longitudinal field set up by a → coil or → solenoid. It can also be accomplished using permanent magnets or electromagnets.
2) In → stellar magnetic field observations, the magnetic field along the → line of sight.

→ longitudinal; → magnetic; → field.

In special relativity theory, the mass of a body when the acceleration is parallel or anti-parallel to velocity: m_l = m₀ / [1 - (v/c)²]^3/2, where m₀ is the → rest mass, v is the velocity, and c the → velocity of light. → transverse mass.

→ longitudinal; → mass.

A wave vibrating along the direction of propagation, such as a → sound wave. → transverse wave.

→ longitudinal; → wave.

The → Zeeman effect when the emitting source is viewed in the direction of the magnetic field. In the normal longitudinal effect, each spectral line is split into two components with frequencies ν ± Δν. The line with the frequency ν - Δν shows left-hand → circular polarization and that with frequency ν + Δν shows right-hand circular polarization. → transverse Zeeman effect.

→ longitudinal; → Zeeman effect.

Elongated, usually from the square or circular form.

Late M.E. oblonge, from L. oblongus "rather long," from ob- a prefix meaning "toward, to, on, over, against" + longus, → long.

Derâzak, from derâz "long," → length + -ak suffix.

Of → Saturn, the angle measured with respect to the sub-observer point (a line connecting the observer to Saturn) in the direction of the orbital motion.

→ ring; → longitude.

The ecliptic longitude of the Sun. It varies from 0° (at the vernal equinox) to 360° during the year. By Kepler's Second Law, the rate of change of the solar longitude is such that the Earth sweeps out equal areas on the ecliptic plane in equal times.

→ solar; → longitude.

→ supergalactic coordinate system.

→ supergalactic; → longitude.

A technique in radio interferometry in which the individual telescopes are not directly connected together, but instead make their observations separately with very accurate timings. The data are later sent to a central correlator to be combined. With this technique the individual telescopes can be arbitrarily far apart, and so the technique provides the highest resolution images in astronomy, typically down to a few milliarcseconds.

→ very; → large; → baseline; → interferometry.

The position of a planet when it is visible in the eastern sky before dawn.

→ western; → elongation.