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

1) (adj.) Of or from outside the limits of the Earth.
2) (n.) A hypothetical extraterrestrial being; → alien.

→ extra- + → terrestrial.

Life that may exist and originate outside the planet Earth.

→ extraterrestrial; → life.

The scientific attempt to detect → intelligent extraterrestrial → life by surveying the sky to find the existence of → transmissions, especially → radio waves or → light, from a → civilization on a distant → planet. The SETI Institute, that carries out the project, is a private non-profit center founded in 1984. There are many methods that SETI scientific teams use to search for extraterrestrial intelligence. Many of these search billions of radio frequencies that reach Earth from all over the → Universe, looking for an intelligent → radio signal. Other SETI teams search by looking for signals in pulses of light emanating from the stars.

→ search; → extraterrestrial; → intelligence.

Any of the various phenomena observable on the Earth that are caused by the influence of the Sun, such as aurora borealis.

→ solar; → terrestrial; → phenomenon.

The point on the surface of a celestial body where the star is perceived to be directly overhead (in zenith). The sublunar point and subsolar point are the equivalent points for the Moon and Sun, respectively.

→ sub-; → terrestrial.

Pertaining to, consisting of, or representing the Earth as distinct from other planets.

From L. terrestris "earthly," from terra "earth," literally "dry land" (as opposed to "sea"); from PIE base *ters- "to dry" (cf. Pers. tešné "thirsty;" Mid.Pers. tašnak "thirsty;" Av. taršu- "dry," taršna- "thirst;" Skt. trsta- "dry," tars- "to be thirsty;" Gk. teresesthai "to become or be dry," L. torrere "to dry up, roast," Goth. þaursus "dry, barren," O.H.G. derren "to make dry," durst "thirst;" Ger. dürr "arid;" O.E. þurstig "thirsty").

Zamini adj. of zamin, variant zami "earth, floor, land;" Mid.Pers. zamig; Av. zam- "the earth;" cf. Skt. ksam- "the ground, earth;" Gk. khthôn, khamai "on the ground;" L. homo "earthly being" (as in homo sapiens, homicide, humble, humus, exhume), humus "the earth;" O.Russ. zemi "land, earth;" PIE root *dh(e)ghom "earth".

A uniform atomic time scale for apparent geocentric ephemerides defined by a 1979 IAU resolution, which replaced Ephemeris Time. TDT is independent of the variable rotation of the Earth, and the length of the tropical year is defined in days of 86,400 seconds of international atomic time. In 1991 it was replaced by Terrestrial Time.

→ terrestrial; → dynamical; → time.

A parameter representing the product of the → gravitational constant by the Earth's mass. It is 3.987 x 10¹⁴ m³s^-2 or 3.987 x 10⁵ km³s^-2.

→ terrestrial; → gravitational; → constant.

The four innermost planets in the solar system, Mercury, Venus, Earth and Mars. They are called terrestrial because they have a compact, rocky surface like the Earth's. The planets, Venus, Earth, and Mars have significant atmospheres while Mercury has almost none. These planets are approximately the same size, with the Earth the largest. They are considerably denser than the Jovian planets, ranging from a specific gravity of 4 for Mars to 5.5 for the Earth.

→ terrestrial; → planet.

The modern astronomical standard for the passage of time on the surface of the Earth. It is the → coordinate time scale consistent with the theory of general relativity for an observer on the surface of the Earth. TT was renamed from Terrestrial Dynamical Time (TDT) in 1991. The fundamental unit of TT is the day of 86,400 SI seconds. It is related to the International Atomic Time by the relation: TDT = TAI + 32.184 sec.

→ terrestrial; → time.