chapter 9 glossary terms

The milky way is a galaxy, and it includes our solar system.

• A huge collection of stars, planets, gas and dust that is held together by gravity.
• Found throughout the universe.
• Vary greatly in size and shape.

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• A collection of stars held together by gravity.
• There are 2 types of star clusters: Open and globular clusters.

• A collection of 100 000 to one million stars, arranged in a distinctive spherical shape.
• Globular clusters appear around the center of the milky way.

• A collection of 50 - 1000 stars; open clusters appear along the main band of the milky way.
• An open cluster is one of two types of star clusters (open and globular clusters)

• A small group of galaxies that includes the milky way.
• Involves about 40 galaxies.
• The diameter of the local group is 10 million light years.
• Adromeda and the milky way are the largest galaxies in the local group.

• A gigantic cluster of 4 to 25 clusters of galaxies which is hundreds of millions of light years in size.
• Astronomers hypothesize that there may be more than 125 billion galaxies.

• Irregular; No regular shape, made up of old and newly forming stars.
• Elliptical;
• No spiral structure, vary in shape from spherical to entongated, tend to be older galaxies with little or no star formations in them, largest galaxies.
• spherical;
• looks like a pinwheel or whirlpool, has a central bulge, classified according to how tightly wound the arms are, has dust and gas available for new star formation.

• Cosmology is the study of the universe.
• Cosmologists try to awnser questions like; how did the universe begin? Is it changing?
• using technology, cosmologists have been able to see backward in time to almost the very beginning of the universe.

• The change in frequency of a light source due to its motion relative to an observer; also, the change in pitch of a sound due to the motion of the source relative to an observer.
• eg. when an abulence moves toward you, the sirens sound waves are compressed, resulting in higher frequencies. when it moves away from you, the opposite occurs.

The effect in which objects moving away from an observer have their wavelengths lengthened, toward the red end of the visible spectrum.

The effect in which objects moving toward an observer have their wavelengths shortened, toward the blue end of the visible spectrum.

• The event that may have triggered the expansion of the universe 14 billion years ago.
• According to the big bang theory, the universe began expanding with unimaginable violence from a hot and incredibly dense state, to its present state.

The radiation left over from the big bang which fills the universe.

• Cosmic microwave background radiation.
• The radiation left over from the big bang which fills the universe.

A form of energy that makes up nearly three quarters of the universe; has the effect of increasing the expansion of the universe.

Dark matter is the most abundant form of matter in the universe: invisible to telescopes.