ASTR 103 - Astronomy

Glossary - B

Balmer series

Series of lines in the visible spectral region arising from transitions between the second energy level of the hydrogen atom and its higher levels.

barred spiral galaxy

A spiral-type galaxy whose spiral arms extend from a barlike feature containing the nucleus.

basalt

A type of igneous rock resulting from the cooling of lava, common on the terrestrial planets.

base

In biochemistry, one of the four chemical structures made up of carbon, nitrogen, and oxygen molecules in the DNA molecule (adenine, guanine, cytosine, thymine). In the RNA molecule, thymine is replaced by uracil.

basin

Large depressed plain known as a mare on the Moon, Mercury, or Mars.

beta particle

An electron.

big bang

A cosmological theory in which the Universe begins expanding from a dense, superhot state of radiation and matter; this expansion of space presumably started some 15 to 20 billion years ago and produced the cosmic background radiation.

binary

Pair of stars, galaxies, or any other astronomical bodies held by mutual gravitational attractions.

binary system

 

biochemical evolution

The development of living organisms through a sequence of chemical combinations producing organic molecules, followed by combinations of organic molecules to form single cell, and later multicellular organisms.

biosphere

Portion of Earth's atmosphere, ground, and water where life can flourish.

bipolar group

(see also sunspot).

blackbody

Ideal body capable of absorbing all radiation falling on it and reemitting it without loss; the spectrum of blackbody radiation is a continuous one and is characterized by the absolute temperature of the blackbody; see Planck's law, Stefan-Boltzmann law, Wien's law, and thermal radiation.

black dwarf

Small dense compact star, no longer radiating, which is the final state of a white dwarf or results when a star is too small to initiate nuclear fusion.

black hole

Superdense configuration that a body assumes when it collapses gravitationally in such a way that its powerful gravitational field prevents radiation or matter from escaping into external space; see event horizon.

BL Lacertae object

 

blueshift

A wavelength shift toward shorter wavelengths due to approach of the emitting object; see Doppler effect.

blue stellar object

Non-radio-emitting quasar identified by its bright ultraviolet radiation and pronounced redshift.

blue supergiant

 

Bode's law

Empirical rule whose progression of numbers represents the approximate distances of the planets in astronomical units from the Sun.

Bohr atom

Model of the atom developed by Niels Bohr in which the electrons orbit the nucleus at specified distances.

bolide

Unusually bright meteor that sometimes explodes with a loud sound into fiery fragments.

bolometric correction

 

bolometric magnitude

The magnitude of a celestial body for all wavelengths. It is a measure of the energy emitted in all wavelengths per unit time.

bow shock wave

Conical interface formed between a high-speed flow of gas in a medium and an obstacle it encounters.

breccia

Mixture of lunar soil and rock fragments formed by impact or high pressure.

bright giant

Luminosity class II stars that are 100s to 1000s of times more luminous than the Sun.

bright-line spectrum

see emission spectrum

brown dwarf

 

B star

A blue-white star of spectral type B with a surface temperature of about 11,000 to 28,000 K, whose spectrum is characterized by absorption lines of neutral helium.