Our solar system is ___________ billion years old.

Any object that directly revolves around a star, has nearly round shape, and has its own orbital zone.

Rocky, small Earth-like planets.

gaseous, very large, Jupiter-like planets

The astroid belt is located between which two planets?

Spheres of gas in space that produce their own energy (self-luminous)

Process by which stars produce energy.

The brightness of a star.

Large spinning clouds of gas and dust being pulled together by gravity.

Stable period when a star creates energy and shines brightly. Our Sun is in this phase.

A group of hundreds of billions of stars held together by gravity.

Everything - all of the matter, energy and space known to exist.

The theory that states the Universe began when an extremely dense concentration of matter exploded and was distributed across the Universe.

The apparent change in wavelength of an energy source that is moving.

When light waves are compressed indicating that an object is moving closer.

When light waves are expanding indicating that an object is moving farther away.