An Etymological Dictionary of Astronomy and Astrophysics
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Same as → A star.

A, letter of alphabet used in the → Harvard classification; → type; → star.

The same as eclipsing binary stars, the prototype of which is Algol.

→ Algol; → variable.

The original pattern or model from which all things of the same kind are copied or on which they are based; a model or first form; prototype (Dictionary.com).

→ arche-; → type.

A division of → C-type asteroids whose members have relatively low albedos (0.04 to 0.08) and the → ultraviolet absorption below 0.5 μm is small or absent. Examples include → 2 Pallas, 379 Huenna (diameter 62 km), and → 101955 Bennu.

→ type; → asteroid.

Same as → B star.

B, letter of alphabet used in the → Harvard classification; → type; → star.

An → asteroid that belongs to the family of → carbonaceous asteroids. They are → depleted in → hydrogen and → helium, have chemical ratios akin to solar composition, and show low → albedo (0.03-0.09). C-type asteroids are the most common variety, forming around 75% of known asteroids. They inhabit → main belt's outer regions.

C stands for → carbonaceous; → type; → asteroid.

An → ionization front of → H II regions whose expansion speed is comparable to the → sound speed in the gas (~ 10 km/sec for hydrogen at 10⁴ K). A D-type ionization front results from → R-type ionization front when its propagation speed decreases as the volume of gas ahead of the ionization front grows. If front velocity is equal to a lower limit (C₁² / 2C₂, where C₁ and C₂ are the sound speed ahead and behind the front respectively), the front is called D critical.

D referring to a dense gas; → type; → ionization; → front.

Same as → enstatite chondrite.

→ enstatite; → type; → chondrite.

In the → Hubble classification, galaxies on the left part of the → Hubble sequence. Early-type galaxies tend to have redder colors, higher average surface brightnesses, and lower → neutral hydrogen content than → late-type galaxies. This terminology is based on the obsolete and erroneous idea that → elliptical and → lenticular galaxies might be evolutionary precursors to → spiral and → barred spiral galaxies.

→ early; → type; → galaxy.

Hot, luminous stars of → spectral type O, B, A, and F0 to F5. They were originally thought, wrongly, to be at an earlier stage of evolution than → late-type stars. See also → spectral classification.

→ early; → type; → star.

A star whose spectrum is characterized by strong → absorption lines of ionized → calcium, Ca II (→ H and K lines), which become much stronger than the hydrogen lines of the → Balmer series. A multitude of fainter metallic lines are also present. Ca II lines strengthen to later types. → Main sequence F stars, of which → Procyon is an example, have a → surface temperature of 6,000 to 7,400°C and a mass of 1.1 to 1.4 → solar masses (Habets & Heintze, 1981, AASS 46, 193).

B, letter of alphabet used in the → → Harvard classification; → type; → star.

A yellowish star whose surface temperature is about 6000 K and its spectrum is dominated by H and K lines of ionized calcium (Ca II 3968 Å and 3934 Å).

G from the alphabetical sequence of spectral types; → type; → star.

A relatively uncommon → carbonaceous carbonaceous asteroid whose spectrum contains a strong → ultraviolet  → absorption feature below 0.5 μm (→ Tholen classification). In the → SMASS classification it corresponds to the Cg and Chg types , depending on the presence or absence (respectively) of the absorption feature at 0.7 μm. The most remarkable "asteroid" in this type is → Ceres (now classified as a → dwarf planet).

→ type; → asteroid.

Same as → G star.

→ G star; → type.

In the → Hubble classification, a galaxy on the left part of the → Hubble sequence. See also → early-type galaxy.

→ late; → type; → galaxy.

A star of → spectral type K, M, S, or C, with a surface temperature lower than that of the Sun. → early-type star. See also → spectral classification.

→ late; → type; → star.

A type of → asteroid that consists of metallic → iron and displays high → albedo (0.10-0.18). M-type asteroids inhabit the middle part of the → asteroid belt.

M for → metallic; → type; → asteroid.

A → metal-poor, → irregular galaxy like the → Large Magellanic Cloud or the → Small Magellanic Cloud. Other examples are: NGC 4449, NGC 4214, and NGC 3109.

→ Magellanic; → type; → galaxy.

The conductivity in a semiconductor caused by a flow of electrons, whereas p-type conductivity is caused by a flow of holes.

n standing for → negative; → type; → conductivity.

Same as → O star.

O, letter of alphabet used in the → Harvard classification; → type; → star.