the galaxy that includes the solar system; appears as a hazy white band in the night sky
what is a galaxy?
a huge collection of stars, planets, gas and dust held together by gravity
what is a star cluster?
a collection of stars held together by gravity
what is an open cluster?
a collection of 500-1000 stars, open clusters appear along the main band of the milky way
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
what is a local group?
the small group of galaxies that include the milky way (about 40)
diameter is about 10 million light years
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
what is cosmology?
the study of the universe; ones who study it are cosmologists
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
what is redshift?
the effect in which objects moving away from an observer have their wavelengths lengthened, towards the red end of the spectrum
what is blueshift?
the effect in which objects moving towards the observer hacve their wavelengths shortened, towards the blue end of the spectrum
what is the big bang?
the event that triggered the explosion of the universe 14 billion years ago
what is cosmic microwave background(CMB) radiation?
the radiation left over from the big bang, which fills the universe
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
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
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