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

A burst that happens gradually, in contrast to a sudden burst.

→ gradual; → burst.

1) To divide into or mark with degrees or other divisions, as the scale of a thermometer.
2) To receive a degree or diploma on completing a course of study (often followed by from).
3) To confer a degree upon, or to grant a diploma to, at the close of a course of study, as in a university, college, or school.
4) A person who has received a degree or diploma on completing a course of study, as in a university, college, or school (Dictionary.com).

M.E., from M.L. graduatus, p.pa. of graduari "to take a degree," from L. gradus "step, → grade."

1, 3) Padâk dâdan, compound infinitive, padâkidan simple infinitive, both from padâk, → grade, + dâdan "to give, grant," → datum, and -idan, → -fy.
2) Padâk gereftan, from padâk + gereftan "→ take, hold."
4) Padâkmand, from padâk + -mand suffix of possession and ability, → -al; padâkidé, p.p. of padâkidan, as above.

1) Marking the scale of an instrument, e.g. the stem of a thermometer is graduated in degrees.
2) An act of graduating; the state of being graduated.

Verbal noun of → graduate.

The → energy transported by → gravitational waves. Gravitational radiation is to → gravity what light is to → electromagnetism.

→ gravitational; → radiation.

Same as → Larmor radius.

→ gyro-; → radius.

A blue-white → giant star of → spectral type B1 III with a visual magnitude of V = 0.61 lying in the constellation → Centaurus. It lies at a distance of 350 → light-years and is the eleventh brightest star of the night sky. Also called → Agena

Hadar, from Ar. haZâr (حضار) "white camel."

Any elementary particle which experiences the strong nuclear force. There are two sorts of hadrons: mesons, which have zero spin, and baryons, which have spin 1/2 or 3/2.

Hadron, from Gk. hadr(os) "thick, bulky" + -on a suffix used in the names of subatomic particles (gluon, meson, neutron), quanta (photon, graviton), and other minimal entities or components (magneton).

The interval lasting until some 10^-5 seconds after the Big Bang when the Universe was dominated by radiation and its temperature was around 10¹⁵ kelvins. It is preceded by → Planck era and followed by → lepton era.

→ hadron; → era.

Of or related to → hadrons.

→ hadron; → -ic.

Ordinary matter composed of → hadrons.

→ hadronic; → matter.

A number that is divisible by the sum of its digits. For example, 18 is a Harshad number because 1 + 8 = 9 and 18 is divisible by 9 (18/9 = 2). The simplest Harshad numbers are the two-digit Harshad numbers: 10, 12, 18, 20, 21, 24, 27, 30, 36, 40, 42, 45, 48, 50, 54, 60, 63, 70, 72, 80, 81, 84, 90. They are sometimes called Niven numbers.

The name Harshad was given by Indian mathematician Dattaraya Kaprekar (1905-1986) who first studied these numbers. Harshad means "joy giver" in Sanskrit, from harṣa- "joy" and da "to give," → datum.

The radiation produced by a → black hole when → quantum mechanical effects are taken into account. According to quantum physics, large fluctuations in the → vacuum energy occurs for brief moments of time. Thereby virtual particle-antiparticle pairs are created from vacuum and annihilated. If → pair production happens just outside the → event horizon of a black hole, as soon as these particles are formed they would both experience drastically different → gravitational attractions due to the sharp gradient of force close to the black hole. One particle will accelerate toward the black hole and its partner will escape into space. The black hole used some of its → gravitational energy to produce these two particles, so it loses some of its mass if a particle escapes. This gradual loss of mass over time means the black hole eventually evaporates out of existence. See also → Bekenstein formula, → Hawking temperature.

Named after the British physicist Stephen Hawking (1942-2018), who provided the theoretical argument for the existence of the radiation in 1974; → radiation.

1) That part of anything that forms or is situated at the top, summit, or upper end.
2) The → nucleus and surrounding → coma of a → comet.

Head, from O.E. heafod "top of the body," also "chief person" (cf. O.S. hobid; Goth. haubiþ Ger. Haupt "head"), from PIE *kauput- "head;" cf. Skt. kaput-, kapala- "skull;" L. caput "head;" Pers. dialect Lori: kapu "head," kapulek "skull, middle of the head;" Kurd. kapol "skull;" Pashto kaparay "skull."

Sar "head," soru, sorun "horn" (karnâ "a trumpet-like wind instrument," variant sornâ "a wind instrument"); Mid.Pers. sar "head," sru "horn;" Av. sarah- "head," srū- "horn, nail;" cf. Skt. śiras- "head, chief;" Gk. kara "head," karena "head, top," keras "horn;" L. cornu "horn," cerebrum "brain;" P.Gmc. *khurnaz (Ger. Horn, Du. horen; cognate with E. horn, as above, from PIE *ker- "head, horn;" O.E. horn "horn of an animal," also "wind instrument;" E. horn); PIE base *ker- "head, horn, top, summit."

A member of the class of radio galaxies (→ radio galaxy) that have a strong radio emission coming from a bright "head" and a more diffuse emission from a "tail." They are often found in clusters.

→ head; → tail; → galaxy.

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 huge → dark cloud of → interstellar dust that is shaped like a horse's head. It is luminous at its edges because it is in front of the bright → emission nebula IC 434. Its height and width are about 5 and 2.5 → light-years respectively. It is located at a distance of about 1500 light-years in the constellation → Orion. Also known as Barnard 33.

→ horse; → head; → nebula.

The size of the observable Universe as derived from the ratio c/H₀, where H₀ is the → Hubble-Lemaitre constant and c the → speed of light. Same as → Hubble distance, → Hubble length, and → cosmic horizon.

→ Hubble; → radius.

A young, nearby cluster of stars (spectral types A1-K) visible to the naked eye in the constellation → Taurus about 150 light-years away. Its individual stars (more than 200) appear to spread out in space. → Aldebaran is a foreground star in that region of the sky.

In Gk. mythology, a group of nymphs and sisters of Hyas, or else his daughters, and when Hyas died while hunting, killed by a lion or a boar, they grieved his death exceedingly, and turned into the stars called Hyades.

Huâdes, from Gk., as above.

The process of adding several usually low-exposure images to create an image having a significantly higher signal/noise ratio.

→ image; → co-; → add.

A paradox raised in 1976 by S. Hawking (1942-2018) whose analysis of the thermodynamic properties of → black holes led him to the prediction that black holes are not in fact black, but radiate due to quantum effects. This implied that, due to the → Hawking radiation, a black hole would eventually evaporate away, leaving nothing. This deduction presented a problem for → quantum mechanics, which maintains that information can never be lost. This topic is a matter of intense debate. Many solutions have been proposed, but all of them have serious drawbacks. In order to analyze better these solutions one needs a quantum gravity theory, which does not exist at the moment. In brief, either the idea of → quantum unitarity must be given up, or a mechanism should be found by which information is not lost after it falls into a black hole.

→ information; → paradox.