ASTR 103 - Astronomy

Glossary - U

UBV photometric system

Standardized magnitude and color system employed by astronomers for comparing intensities in the ultraviolet (U), blue (B), and yellow or visual (V) spectral regions.

ultraviolet

Portion of the electromagnetic spectrum that extends from the shortest visible waves at about 3900 angstroms to about 100 angstroms.

umbra

Dark central region of a sunspot. In an eclipse it is the dark central part of the shadow cast by an illuminated body.

universal time

Universal constant of gravitation: see gravitational constant.

Universe

Everything that we know exists and all that will be found in the future make up the Universe.