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The Milky Way is the galaxy that includes the solar system.
It is a spiral galaxy that appears to be a hazy white band in the night sky.
It belongs to a group of about 40 galaxies called the Local Group.
10% of the Milky Way is made of visible matter.
A galaxy is a collection of billions of stars, gas and dust held together by gravity.
They are found throughout the universe, and vary greatly in shape and size.
- There are 3 types of galaxies:
-Looks like a pinwheel or whirlpool
-Has a central bulge with arms coming off this centre
-Classified according to how tightly wound the arms are
-Has desist and gas available for new star formation
-No spiral structures
-Vary in shape from spherical to elongated
-Tend to be older galaxies with little to no star formation in them
They contain some of the oldest stars in the universe
-The largest galaxies in the universe
-No regular shape such as spiral arms or an obvious central bulge
-Made up of newly forming stars and old stars
Star clusters are groups of stars that are held by gravity and travel together.
They range from 10 to a million stars.
An open cluster is a type of star cluster with a collection of stars from 50 to 1000 stars.
They appear along the main band of the Milky Way
Globular clusters are a collection of 100 000 to a million stars arranged in a distinctive spherical shape.
They appear around the centre of the Milky Way.
The local group is a group of about 40 galaxies including the Milky Way.
The diameter of the local group is about 10 million light-years
Andromeda and the Milky Way are the largest galaxies in the local group.
Superclusters are gigantic clusters of 4 to 25 clusters of galaxies, which is hundreds of millions of light-years in size.
Shapes of galaxies
Refer to cards 3-5.
Spiral Galaxy- Spiral galaxies are shaped as pinwheels or whirlpools, and have a central bulge with arms coming off the centre.
Elliptical Galaxy- Elliptical galaxies vary in shape from spherical to elongated, and have no spiral structures.
Irregular Galaxy- No regular shape.
Cosmology is the study of the universe.
Cosmologists try to answer questions such as; how did the universe begin?
Using technology cosmologists have been able to see backward in time to almost the very beginning of the universe.
The doppler effect, discovered by Edwin Hubble, is the displacement of the spectral lines from their normal position.
This occurs in the pitch of an ambulance As it approaches or moves away. As the ambulance moves towards you the sound waves are compressed resulting in a higher frequency.
Redshift is the effect in which objects moving away from an observer have their wavelengths lengthened, toward the red end of the visible spectrum.
Blueshift is the effect in which objects moving toward an observer have their wavelengths shortened, toward the blue end of the visible spectrum.
The Big Bang is the even that may have triggered the expansion of the universe 14 billion years ago.
The universe started expanding with unimaginable violence, about 14 billion years ago, from its extremely compact, small, and unimaginsmall dense state to its present state.
Cosmic microwave background (CMB) radiation
Wilson and Penzias working for Bell Telephone Labs discovered the microwave noise that was produced by radiation left over from the Big Bang.
The temperature of the CMB radiation was about -270 degrees Celsius.
Dark matter is the missing mass of galaxies, and it is the most abundant form of matter in the universe.
It is invisible to telescopes and it has only been detected by astronomers except for by the effects it causes.
After the Big Bang the expansion of the universe should be slowing down due to gravity but for some reason something began to overcome gravity and is accelerating the expansion.
Scientists called it dark energy.
Dark energy makes up 73 percent of the entire universe but its real nature is still not understood.
The effect of dark energy: