A system of millions or billions of stars, together with gas and dust, held together by gravitational attraction.

Planets orbit the sun in an orbit of this shape.

A cloud of gas and dust that is the beginning of a star.

As distance increases, gravitational force does this.

The most abundant element found in main sequence stars.

A decrease in frequency due to movement away from an observer.

The eccentricity of a perfect circle.

Where fusion occurs in main sequence stars.

Mass and gravity have this type of relationship

As the velocity of a planet/satellite's orbit increases, this happens to its orbital period.

The three possible fates of the universe.

The two things that gravity depends on.

An explosion that occurs at the end of a massive star's life-cycle.

As the wavelength of light from a star increases, its frequency does this.

The position on a planet's elliptical orbit where it is moving the slowest.

A decrease in wavelength due to movement toward an observer.

The orbital period of the Earth.

What the sun will become when it is done fusing hydrogen in its core.

For stars on the main sequence, as the star gets hotter, its brightness does this.

If the fate of the universe is an open universe, this will happen.

Two pieces of evidence for the big bang theory.

The point in an elliptical orbit where the planet is moving the fastest.

The type of star that the sun will be at the END of its life-cycle.

Compared to a less massive planet orbiting a star, a more massive planet orbiting the same star's major axis will be this.

How eccentricity is calculated.