Chapter 25 Vocabulary

Light-Year

• The distance light travels in one year; 9.5 trillon KM

Apparent Magnitude

• The apparent brightness of star when viewed from Earth

Absolute magnitude

• The apparent brigthness of a star if it was view from 32.6 light years.

Nova

• A star that exposively increases in brightness

Cepheid Variable

• A star whose brightness varies periodically because of it expands and contracts.

Black Hole

• A massive star that has collapsed to such a small volume that its gravity prevents the escape of everything, including light.

Nebula

• Clouds of gas and/or dust in space.

Galaxy

• A group of stars, dust , and gases held together by gravity.

Galactic Cluster

• A system of galaxies containing form several to thousands of memeber galaxies.

Hubble's Law

• States that the galaxies are retreating from the milky way at a speed that is proportional to their distance.

Big Bang Theory

• proposes that the universe originated as a single mass, which subsequently exploded.