Supergiant stars

The universe is made up of mostly

The brightness of a star depends on its

Astronomers estimate that the universe contains

Stars are held together by

A _____ is so massive and compressed that not even light can escape its gravity.

Who first proposed that the universe is expanding?

All stars radiate

The core is the hottest part of the sun with a temperature of about

An observation of the red shift of galaxies suggests that the universe is

Quasars are among the strongest sources of _____ in the universe.

Nearly 90 percent of all stars are at what point in their life cycles?

An astronomer observes four stars, each of which is a different color. Of these stars, the _____ star is the hottest.

Our solar system is located in which of these galaxies?

A light-year is a unit of

Elliptical galaxies often appear reddish due to an abundance of

A galaxy is a collection of ______ bound together by gravity.

Our galaxy is classified as a(n)

A star is born when

The varying theories if the universe's eventual fate all depends on the universe's current

The lifespan of the sun before reaching the red giant stage is about

The sun will eventually end up as a

Interstellar matter is composed of ____ found between stars in a galaxy.

Clusters of galaxies can form larger groups called

The big bang theory states that the universe began with a gigantic explosion

Energy produced in a star's core moves through the star by

All stars

Astronomers group galaxies into three types, according to their

Stars produce energy by fusing hydrogen into

The surface temperature of the sun is related to its peak wavelength, which is near the color

Quasars are thought to be the centers of

Sum of all space, matter, and energy

Apparent shift toward longer wavelengths of light when a luminous object moves away from the viewer

Theory that all matter and energy in the universe exploded ten or twenty billion years ago and began expanding in all directions

Apparent shift toward shorter wavelengths of light when a luminous object moves toward the viewer

Egg shaped or spherical

Huge central bulge, surrounded by arms

Composed of stars

Lack a well-defined structure