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Milky way
 The milky way is a galaxy, and it includes our solar system.
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Galaxy
- 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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Star cluster
 - A collection of stars held together by gravity.
- There are 2 types of star clusters: Open and globular clusters.
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Globular cluster
- 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.
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Open cluster
- 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)
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Local group
- 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.
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Supercluster
- 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.
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Shapes of 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.
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Cosmology
- 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.
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Doppler effect
- 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.
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Redshift
The effect in which objects moving away from an observer have their wavelengths lengthened, toward the red end of the visible spectrum.
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Blueshift
The effect in which objects moving toward an observer have their wavelengths shortened, toward the blue end of the visible spectrum.
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Big bang
- 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.
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Cosmic microwave background
The radiation left over from the big bang which fills the universe.
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(CMB) Radiation
- Cosmic microwave background radiation.
- The radiation left over from the big bang which fills the universe.
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Dark energy
A form of energy that makes up nearly three quarters of the universe; has the effect of increasing the expansion of the universe.
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Dark matter
Dark matter is the most abundant form of matter in the universe: invisible to telescopes.
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