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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
are scientists that study the natural world beyond the
earth.
Cosmologists
are scientists who study the structure and changes in
the present universe in order to predict the future of the universe.
Cosmic
structures
are the very large structures that make up the universe.
A Dwarf
Galaxy
is a galaxy that has only one million to ten million suns.
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
are cosmic structures in which many galaxies are found in close
proximity to each other.
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
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.
A
Group
is a level of cosmic structures that have densities and
orbital velocities between galaxies and clusters. Most galaxies
belong to small groups.
An Irregular
Galaxy
is a galaxy whose shape cannot be described by any commonly known
shape.
A Light-year
is the distance that light can travel in one year, which is approximately
six trillion miles.
Milky
Way Galaxy
is the spiral galaxy of which our sun is a part.
Primordial
gas
is gas that was present at the beginning of the universe.
A Spiral
Galaxy
is one of the three major classifications of galaxies. Their characteristics
include a plate-shaped disk containing spiral arms.
Star
Clusters
are aggregations of stars that are gravitationally bound but are
smaller and less massive than galaxies.
A Supercluster
is a cluster of tens of thousands of galaxies that are
typically about one hundred million light years in diameter.
Voids
are spaces between superclusters that are relatively free
of luminous matter. They are also called holes or bubbles.
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