Galaxies

Five hundred billion galaxies
According to the best estimates of astronomers there are at least one hundred billion galaxies in the observable universe. They’ve counted the galaxies in a particular region, and multiplied this up to estimate the number for the whole universe.
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  • giant groups of millions or even trillions of stars are called galaxies.
  • our own local galaxy is the Milky Way.

Australia faces the Milky Way and therefore star gazers can see 100 times more stars
than they could in the Northern Hemisphere.
Captured by Derek Rowley
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  • there may be 500 billion galaxies in the Universe.
  • only three galaxies are visible to the naked eyes from the Earth besides the Milky Way – the Large and Small Magellanic clouds, and the Andromeda Galaxy.

LMC and SMC
was captured by Derek Rowley
at Easter Island.

The Andromeda Galaxy
The Andromeda Galaxy is located at a distance of about 2.54 million light years from Earth.
With an apparent visual magnitude of 3.44, it is the most distant object visible to the naked eye,
and one of the brightest deep sky objects listed in Messier’s catalogue.

 

  • in 1923, astronomers realised that galaxies are huge star groups.
  • galaxies are often found in groups called clusters.
  • one cluster may contain hundreds of galaxies.
  • spiral galaxies are spinning galaxies with a dense core and spiralling arms.

Spiralling arm galxy of Messier 101 in Ursa Major
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  • irregular galaxies have no obvious shape – they may have formed from the debris of galaxies that crashed into each other.

NGC 1427A – an example of an irregular galaxy
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  • elliptical galaxies are vast, old, egg-shaped galaxies, made up of as many as a trillion stars.

An example of an elliptical galaxy
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  • barred spiral galaxies have just two arms – these are linked across the middle of the galaxy by a bar from which they trail.

NGC 1365 in the constellation of Fornax,
an example of spiral arm galaxy.

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