The following glossary includes terms that are used in Part One of the Spongy Universe Student Text. You will probably want to study the terms and their definitions before you read the student text.

Astronomers (&-'strä-n&-m&rs)
Astronomers are scientists that study the natural world beyond the earth.

Cosmologists (käz-'mä-l&-jists)
Cosmologists are scientists who study the structure and changes in the present universe in order to predict the future of the universe.

Cosmic structures ('käz-mik 'str&k-ch&rs)
Cosmic structures are the very large structures that make up the universe.

Dwarf Galaxy ('dworf 'ga-l&k-sE)
A dwarf galaxy is a galaxy that has only one million to ten million suns.

Elliptical Galaxy (i-'lip-ti-k&l 'ga-l&k-sE)
An elliptical galaxy is one of the three major classifications of galaxies. They are spherical or cigar-shaped and contain no disks or spiral arms.

Galactic Clusters (g&-'lak-tik 'kl&s-t&rs)
Galactic clusters are cosmic structures in which many galaxies are found in close proximity to each other.

Galaxy ('ga-l&k-sE)
A galaxy is a large aggregation of usually over a million stars, bound together by gravity. There are three major classifications of galaxies-spiral, elliptical, and irregular.

Gravity ('gra-v&-tE)
Gravity is the universal, mutual attraction that all massive objects have for one another. Its force is directly proportional to the mass of each object, and decreases by the square of the distance separating the objects.

Group ('grüp)
A group is a level of cosmic structures that have densities and orbital velocities between galaxies and clusters. Most galaxies belong to small groups.

Irregular Galaxy (i-'re-gy&-l&r 'ga-l&k-sE)
An irregular galaxy is one whose shape cannot be described by any commonly known shape.

Light-year ('lIt-"yir)
A light year is the distance that light can travel in one year, which is approximately six trillion miles.

Milky Way Galaxy ('mil-kE 'wA 'ga-l&k-sE)
The Milky Way Galaxy is the spiral galaxy of which our sun is a part.

Primordial gas (prI-'mor-dE-&l 'gas)
Primordial gas is gas that was present at the beginning of the universe.

Spiral Galaxy ('spI-r&l 'ga-l&k-sE)
A spiral galaxy is one of the three major classifications of galaxies. Their characteristics include a plate-shaped disk containing spiral arms.

Star Clusters ('stär 'kl&s-t&rs)
Star clusters are aggregations of stars that are gravitationally bound but are smaller and less massive than galaxies.

Supercluster ('sü-p&r-"kl&s-t&r)
A Supercluster is a cluster of tens of thousands of galaxies that are typically about one hundred million light years in diameter.

Voids (voyds)
Voids are spaces between superclusters that are relatively free of luminous matter. They are also called holes or bubbles.