An Etymological Dictionary of Astronomy and Astrophysics
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A binary system in Leo the brighter component of which (magnitude 2.6) is a giant K star and the partner a giant G (magnitude 3.8). The angular separation of just over 4'' means that the two stars are at least 170 AU apart, for a distance of 126 → light-years, and have an orbital period of over 500 years.

Algieba, from Ar. Al-Jabhah "the forehead" (of the Lion).

The production of → light elements, roughly three minutes after the → Big Bang when the temperature of the → Universe dropped from 10³² K to approximately 10⁹ K. In a short time interval → protons and → neutrons collided to produce → deuterium. Most of the deuterium then fused with other protons and neutrons to produce → helium and a small amount of → tritium. The element → lithium 7 could also arise form the coalescence of one tritium and two deuterium nuclei. According to the Big Bang nucleosynthesis theory, roughly 25% of the mass of the Universe consists of helium. It also predicts about 0.01% deuterium, and even smaller quantities of lithium. These predictions depend critically on the → baryon-photon ratio. Same as → primordial nucleosynthesis.

→ Big Bang; → nucleosynthesis.

The Chameleon. A small inconspicuous → constellation in the southern hemisphere near → Crux, lying at approximate position: R.A. 11 h, Dec. -80°. Abbreviation: Cha; genitive form: Chamaeleonis;

From O.Fr. chaméléon, from L. chamaeleon, from Gk. khamaileon, from khamai "on the ground" (akin to chthon "earth;" cf. Av. zam- "the earth," Mid.Pers. zamig, Mod.Pers. zami, zamin "the earth," Skt. ksam, L. homo "earthly being" and humus "the earth," PIE *dh(e)ghom "earth") + leon "lion."

Âftâbparast "chameleon," literally "sun adorer," from âftâb "Sun, sunlight" + parast "worshipper,"

The → mass extinction event that destroyed the dinosaurs and a majority of other species on Earth approximately 65 million years ago. This event is believed to have been the impact of a 10 km-size → asteroid or → comet nucleus and its aftereffects, including a severe → impact winter. The collision would have released the energy equivalent to 100 million megatonnes (teratonnes) of → TNT, i.e. more than 10⁹ times the energy of the atomic bomb dropped on Hiroshima on August 6, 1945. Same as the → Cretaceous-Tertiary event.

→ Cretaceous; → Paleogene; → extinction; → event.

The second brightest star, of magnitude V = 2.14, in the constellation → Leo. A → main sequence star of → spectral type A3 V.

Denebola, from Ar. dhanab al-asad (ذنب الاسد) "tail of the lion," referring to the lion in Gk. mythology.

Širdom "tail of the lion," from šir "lion" → Leo + dom "tail," → comet. Zanab-ol-asad from Ar., as above.

The explosive processes that are believed to occur in supernovae. Explosive carbon burning occurs at a temperature of about 2 × 10⁹ degrees and produces the nuclei from neon to silicon. Explosive oxygen burning occurs near 4 × 10⁹ degrees and produces nuclei between silicon and calcium in atomic weight.At higher temperatures, still heavier nuclei are produced.

→ explosive; → nucleosynthesis.

A space mission whose main goal was to explore → Jupiter and its moons and rings. The spacecraft was launched on October 19, 1989, arrived at Jupiter in December 1995. It disappeared on September 21, 2003, after eight years orbiting Jupiter, when mission controllers crashed it into → Jupiter's atmosphere. On December 7, 1995, Galileo's probe dived into Jupiter's atmosphere, and measured atmospheric pressure, density, and composition, and explored the planet's → radiation belts. Galileo had two parts: an orbiter and a descent probe that parachuted into Jupiter's atmosphere. The orbiter sent back hundreds of pictures of the four large → Galilean satellites of Jupiter (→ Io, → Europa, → Ganymede, and → Callisto). It made many discoveries during its eight years looping around Jupiter. It found evidence for layers of salt water below the surface on Europa, Ganymede, and Callisto, and measured high levels of volcanic activity on Io. When → Shoemaker-Levy slammed into Jupiter in 1994, Galileo had the only direct view of the → comet striking Jupiter's atmosphere. Galileo determined that → Jupiter's rings are formed from dust hurled up by → meteorite impacts on planet's inner moons. Measurements by the orbiter's → magnetometer revealed that Io, Europa, and Ganymede have metallic cores, while Callisto does not. Also, Galileo discovered that Ganymede possesses its own → magnetic field; it is the first moon known to do so. The orbiter also found that the Galilean satellites all have thin atmospheres. During it's trip from Earth to Jupiter, Galileo passed by and studied two asteroids: → Gaspra in 1991 and → Ida in 1993, around which it discovered → Dactyl, the first moon orbiting an asteroid (windows2universe.org).

→ Galileo; → mission.

In the absence of air resistance, any two bodies that are dropped from rest at the same moment will reach the ground at the same time regardless of their mass.

Galileo (1564-1642) was the first to determine, at the start of the seventeenth century, the law of constant acceleration of free-falling bodies. → law; → fall; → body.

An approach in which terms reconstructed in the → proto-language are used to make inferences about its speakers' culture and environment.

→ language;→ paleontology.

The Lion. One of the most conspicuous → constellations in the northern hemisphere, at 10h 30m → right ascension, 15° north → declination. Leo is a constellation of the → Zodiac crossed by the Sun from August 10th to September 16th. Leo is visible from February through June. Its brightest star, α Leonis or → Regulus, is of the first magnitude. Abbreviation: Leo; Genitive: Leonis. The neighboring constellations are → Cancer, → Coma Berenices, → Crater, → Hydra, → Leo Minor, → Lynx, → Sextans, → Ursa Major, and → Virgo. Leo contains many bright stars, many of which were individually identified by the ancients. There are four stars of first or second magnitude, which render this constellation especially prominent. Apart from Regulus, the constellation is home to the bright stars → Denebola, the nearby star Wolf 359, and to a number of famous deep sky objects, among them galaxies Messier 65, Messier 66, Messier 95, Messier 96, Messier 105, and NGC 3628. There are two → meteor showers associated with the constellation. The → Leonids usually peak on November 17-18 every year and have a → radiant near the bright star Gamma Leonis. The January Leonids are a minor shower that peaks between January 1 and 7. Leo has 11 stars with known planets.

→ lion.

The Lesser Lion. A faint constellation in the northern hemisphere, at 10h 20m right ascension, 35° north declination. Abbreviation: LMi; genitive: Leonis Minoris.

→ Leo; Minor, from L. minor "lesser, smaller, junior," from PIE base *min- "small."

Šir, → Leo; kucak "small," (Mid.Pers. kucak "small"), related to kutâh "short, small, little," kudak "child, infant," kutulé, → dwarf, Mid.Pers. kôtâh "low," kôtak "small, young; baby;" Av. kutaka- "little, small."

A → dwarf galaxy recently discovered near the Milky Way in → neutral hydrogen → 21-centimeter line observations. Optical imaging observations indicate that it is located between 1.5 and 2.0 Mpc from the Milky Way. This places Leo P in the → Local Volume but beyond the → Local Group. The dwarf galaxy has extreme properties: it is the lowest-mass system known that contains significant amounts of gas and is currently forming stars (Katherine L. Rhode et al. 2013, AJ 145, 149).

→ Leo.

A → meteor shower emanating from an apparent point in the constellation → Leo that occurs from November 14-20, with a maximum on November 17-18. It is due to the annual passage of the Earth through the orbit of the comet → Tempel-Tuttle and encounter with the dust debris from the comet.

From L. Leon, → Leo, + → -ids.

A constituent of the atomic nucleus, i.e. a proton or a neutron.

From nucle(us), → nucleus, + -on a suffix used in the names of subatomic particles, probably extracted from → ion.

Haston, from hast(é)→ nucleus + -on, as above.

The practical applications of nuclear physics, and the techniques associated with those applications.

From → nucleon + → -ics.

The process by which → nuclear reactions at very high temperatures and pressures produce the various → chemical elements of the → periodic table, either in the → Big Bang or in stellar interiors. See also → primordial nucleosynthesis, → stellar nucleosynthesis, → explosive nucleosynthesis.

From nucleo-, combining form of → nucleus + → synthesis.

Haste-handâyeš, from hasté→ nucleus + handâyeš→ synthesis.

Produce through → nucleosynthesis.

→ nucleosynthesis; → -ize.

Of, pertaining to, proceeding by, or involving → nucleosynthesis.

Adj. of → nucleosynthesis.

The era following the leptonic era, between 1 second and 1000 seconds after the Big Bang, when neutrons were abundant and helium and deuterium were synthesized.

→ nucleosynthetic; → era.

A process involving → nucleosynthesis, such as → r-process and → r-process.

→ nucleosynthetic; → process.