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

The time at which the apparent upper limb of the rising Sun is on the astronomical horizon, that is when the true zenith distance, referred to the center of the Earth, of the central point of the disk is 90°50', based on adopted values of 34' for horizontal refraction and 16' for the Sun semidiameter.

→ Sun; → rise.

The time at which the apparent upper limb of the setting Sun is on the astronomical horizon, that is when the true zenith distance, referred to the center of the Earth, of the central point of the disk is 90°50', based on adopted values of 34' for horizontal refraction and 16' for the Sun semidiameter.

→ Sun; → set.

An area seen as a dark patch on the Sun's surface. Sunspots appear dark because they are cooler (of about 4000 °C) than the surrounding → photosphere (about 6000 °C). They range in size from a few hundred kilometers to several times the Earth's diameter and last from a few hours to a few months. Very small sunspots are called → pores. The number of sunspots varies from maximum to minimum in about 11 years, the → sunspot cycle. Their appearance during a cycle follows the → Sporer law. A typical spot has a central → umbra surrounded by a → penumbra, although either features can exist without the other. Sunspots are associated with strong magnetic fields of 0.2 to 0.4 → tesla. A given sunspot has a single magnetic → polarity. The opposite polarity may be found in other sunspots or in the bright and diffuse → facular region adjacent to the sunspot. The first recorded naked-eye sightings of sunspots were by Chinese astronomers in the first century B.C. Johannes Fabricius (1587-1617) was the first to argue that sunspots are areas on the solar surface.

→ Sun; → spot.

→ solar cycle.

→ sunspot; → cycle.

Periods of time when the → relative sunspot number is low. These periods of time occur approximately every 11 years and represent the minimum in the → sunspot cycle.

→ sunspot; → minimum.

A quantity which gives the number of sunspots at a given time. It is defined by the relationship R = k(10g + f), where R is the sunspot number, k is a constant depending on the observation conditions and the instrument used, g is the number of the groups and f is the number of individual spots that can be counted. Also called the → Wolf number and → relative sunspot number.

→ sunspot; → number.

The loss of energy by high-energy electrons in a → galaxy cluster, which distorts the → cosmic microwave background (CMB) radiation through → inverse Compton effect. When photons from the CMB radiation travel through a hot plasma (with a temperature of around 10⁸ K), in which bathe a galaxy cluster, they collide with energetic electrons and some of the energy of the electrons is transferred to the low energy CMB photons. If we look at the CMB radiation through such a plasma cloud, we therefore see fewer microwave photons than we would if the cloud were not there.

Named after Rashid Sunyaev (1943-) and Yakov Borisovich Zel'dovich (1914-1987), Russian astrophysicists; → effect.

Same as → perigee full Moon.

→ super-; → Moon.

A group of hundreds to thousands of very young stars packed into an unbelievably small volume of a few parsecs in size. These objects represent the youngest stage of massive star cluster evolution yet observed. The most massive and dense SSCs, with ages less than 10⁶ years, may be proto globular clusters. SSCs are thought to dissolve within 10 million years and merge into the field star population.

→ super; → star; → cluster.

A prefix occurring originally in loanwords from Latin, with the basic meaning "above, beyond."

L. adverb and preposition super "above, over, on the top (of), beyond, besides, in addition to," from PIE base *uper "over," cognate with Pers. abar-, as below.

Mid.Pers. abar (Mod.Pers. bar- "on, upon, up"); O.Pers. upariy "above; over, upon, according to;" Av. upairi "above, over," upairi.zəma- "located above the earth;" cf. Gk. hyper- "over, above;" L. super-, as above; O.H.G. ubir "over."

A star whose mass exceeds the → canonical upper limit of the stellar → initial mass function (Kroupa et al. 2012, arXiv:1112.3340).

→ super-; → canonical; → star.

A superluminous → Type Ia supernova which is characterized by a bright → light curve peak, a slow light curve evolution during the photospheric phase, and moderately low ejecta velocities. Modeling suggests ejecta masses far in excess of the → Chandrasekhar limit of mass for non-rotating → white dwarfs and the production of about 1.5 Msun of ⁵⁶Ni. This precludes the interpretation of these events as thermonuclear explosions of Chandrasekhar-mass white dwarfs.

→ super-; → Chandrasekhar limit.

An → extrasolar planet more massive than the Earth but less massive than 10 → Earth masses. The first discovered super-Earth orbits an M4 V star named GJ 876. Its estimated mass is 7.5±0.7 Earth masses and it has an orbital period of 1.94 days. It is close to the host star, and the surface temperature is calculated to lie between 430 and 650 K (Rivera et al. 2005, ApJ 634, 625).

→ super-; → Earth.

A → stellar wind accelerated by radiation pressure in the continuum from a star with a luminosity above the → Eddington limit.

→ super-; → Eddington limit; → wind.

A condition in which there is an excess of the actual temperature gradient over the → adiabatic temperature gradient corresponding to the same pressure gradient. A region with superadiabatic temperature gradient is convectively unstable. → Hayashi forbidden zone.

→ super-; → adiabatic; → temperature; → gradient.

A cavity hundreds of light-years across filled with a hot gas blown into the interstellar medium by multiple supernovae and stellar winds. Examples are the Local Bubble in the Orion Arm of the Milky Way and the N44 Superbubble in the Large Magellanic Cloud.

→ super-; → bubble

1) An aggregation of clusters of galaxies (→ galaxy cluster). Superclusters are typically about one hundred million (10⁸) → light-years in diameter and contain tens of thousands of galaxies. Some examples are the → Local Supercluster, → Centaurus supercluster, → Laniakea supercluster, → Perseus-Pisces supercluster→ Shapley supercluster→ Virgo supercluster.
2) For stellar aggregations, → dynamical stream.

→ super-; → cluster

Grouping of galaxies in supercluster structure.

→ super-; → clustering

The phenomenon in which certain materials, when cooled to a sufficiently low temperature, lose all resistance to the flow of electricity.

→ super-; → conductivity

A material which shows almost perfect conductivity at temperatures approaching absolute zero.

→ super-; → conductor.