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Milky Way
The galaxy in the universe that contains the solar system; appears as a hazy white band in the night sky.
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Galaxy
A huge collection of stars, planets, gas, and dust held together by gravity.
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Star clusters
A collection of stars held together by gravity
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Open clusters
A collection of 50 − 1000 stars; open clusters appear along the main band of the milky way.
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Globular clusters
A collection of 100 000 to a million stars arranged in a distinctive spherical shape.
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Local group
A small group of about 40 galaxies that include the milky way.
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Super clusters
A gigantic collection of 4 to 25 clusters of galaxies that is hundreds of millions of light-years in size.
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Shapes of galaxies
- Galaxies have three known classifications.
- Spiral galaxies, Elliptical galaxies, and Irregular galaxies.The milky way is a spiral.
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Cosmology
The study of the universe.
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Doppler effect
The change in the pitch of a sound due to the motion of the source relative to an observer; also, the change in frequency of a light source due to it motion relative to an observer.
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Redshift
The displacement of spectral lines toward longer wavelengths (the red end of the spectrum) in radiation from distant galaxies and celestial objects.
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Blue shift
The displacement of the spectrum to shorter wavelengths in the lightcoming from distant celestial objects moving toward the observer.
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Big Bang
The explosion of dense matter that, according to currentcosmological theories, marked the origin of the universe.
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Cosmic microwave radiation
The radiation left over from the big bang that fills the universe.
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Dark matter
The most abundant form of matter in the universe; invisible to telescopes.
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Dark energy
A form of energy that makes nearly three quarters of the universe; has the effect of increasing the expansion of the universe.
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