B

Barred spiral

A spiral galaxy with a bright bar through its nucleus. The arm extend from the two ends of the bar.

 

Barycenter

The center of mass (gravity) around which two bodies orbit.

 

Big bang theory

A cosmological theory which states that the universe evolved from a primeval axplosion.

 

Binary star

A double star system held together by mutual gravitation with its components revolving around their barycenter.

 

BL Lacertae

A peculiar variable galaxy showing no strong spectral features but emitting radiowaves. It was originally mistaken for a star.

 

Black body

A theoritically perfect radiator-abody that absorps and reemits all the radiation that fall on it.

 

Black dwarf

A star whose mass is too small for nuclear reaction to occur. It is therefore nonluminous.

 

Black hole

An object that has suffered gravitational collapse. The gravitational attraction at its "surface" or horizon is so large that not even light is able to escape. Matter falling into a black hole is similarly unable to escape, and loses its identity. Black holes may be remnants of supernovae.

 

Bode-Titius relationship

A sequence of number (empirical relationship) which gives the approximate mean distances of the planets in astronomical units.

 

Bolide

A very bright meteor that often breaks up with a loud sound; a fireball.

 

Bolometric magnitude

Stellar magnitude based on the radiation emitted at all wavelengths from the star. The measurement is based on the radiation of the entire electromagnetic spectrum corrected for the effect of the earth's atmosphere.

 

Brigthness

A measure of luminosity of a body.