Van Allen belts At least two doughnut-shaped regions of magnetically trapped charged particles high above Earth's atmosphere.

variable star A star whose luminosity changes with time.

vernal equinox Date on which the Sun crosses the celestial equator moving northward, occurring on or near March 21.

visible The small range of the electromagnetic spectrum that human eyes perceive as light. The visible spectrum ranges from about 400 to 700 nm, corresponding to blue through red light.

visible light The small range of the electromagnetic spectrum that human eyes perceive as light. The visible spectrum ranges from about 400 to 700 nm, corresponding to blue through red light.

visible spectrum The small range of the electromagnetic spectrum that human eyes percieve as light. The visible spectrum ranges from about 4000 to 7000 angstroms, corresponding to blue through red light.

visual binary A binary star system in which both members are resolvable from Earth.

void Large, relatively empty region of the universe around which superclusters and "walls" of galaxies are organized.

volcano Upwelling of hot lava from below Earth's crust to the planet's surface.