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what is the milky way?
the galaxy that includes the solar system; appears as a hazy white band in the night sky 
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what is a galaxy?
- a huge collection of stars, planets, gas and dust held together by gravity
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what is a star cluster?
- a collection of stars held together by gravity
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what is an open cluster?
a collection of 500-1000 stars, open clusters appear along the main band of the milky way
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what is a globular cluster?
- a collection of 100 000 to a million stars, appear in distinctive spherical shape; globular clusters appear around the centre of the milky way
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what is a local group?
- the small group of galaxies that include the milky way (about 40)
- diameter is about 10 million light years
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what is a supercluster?
- a gigantic cluster of 4 to 25 clusters of galaxies, which is hundreds of millions of light years in size
- there may be more than 125 billion galaxies, nearly all of them are organized in clusters
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what is cosmology?
the study of the universe; ones who study it are cosmologists
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what is the 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 the observer
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what is redshift?
the effect in which objects moving away from an observer have their wavelengths lengthened, towards the red end of the spectrum
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what is blueshift?
- the effect in which objects moving towards the observer hacve their wavelengths shortened, towards the blue end of the spectrum
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what is the big bang?
the event that triggered the explosion of the universe 14 billion years ago
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what is cosmic microwave background(CMB) radiation?
- the radiation left over from the big bang, which fills the universe
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what is dark matter?
- accounts for 23% of the universe
- the most abundarnt form of matter in the universe, invisible to telescopes
- its true identity is unknown
- the search for dark matter has been going on since the 1990s
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what is dark energy?
a form of energy that makes up nearly three quarters of the universe (73%); has the effect on increasing the expansion of the universe
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what are the shapes of the galaxies?
- classified as spiral or elliptical, according to shape and appearance
- galaxies that do not fit under those categories are irregular galaxies
- -spiral galaxy;looks like a pinwheel from above, arms spiralling out from core, looks like a plate with a bulge in the middle from the side,
- -elliptical range from a perfect sphere shape to a stretched ellipse, contain some of the oldest stars in the universe, largest galaxies are elliptcal, it is estimated that well over half are elliptical
- - irregular galaxies do not have a regular shape (eg. plate with bulge, arms branching out, elliptical shape) made up of newly forming stars and old stars
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