1. Who is famous for classifying different types of galaxy?
2. Describe the 5 main types of galaxy.
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- Spiral (S)
- e.g. Andromeda
- Flattened disk-shaped
- Barred Spiral(Sb)
- Like Spiral
- Has bright bar running through nucleus through which spiral arms appear.
- Elliptical (E)
- Smooth Spheroid of stars
- Brightest at centre
- Dimmest at edge.
- Irregular (Irr)
- Has little structure or symmetry
- Lenticular
- Class between Elliptical and Spiral
3. What is a Tuning fork diagram?
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- Published Hubble’s book (Realm of the Nebulae)in 1936
- Represents Hubble’s classification scheme.
4. Draw a Tuning fork diagram.
5. Give the classification of our own galaxy’s structure.
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- Traditionally (Sb)
- More evidence suggests a definite bar
6. What is the Local Group?
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- Galaxies are groped together just like stars .
- Our galaxy is grouped together with 50 others
- This is the local groupOur Local Group has 5 neighbouring galaxies.
7. Name 6 galaxies in our Local Group.
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- Andromeda
- M31
- Largest in Local Group
- Large Magellanic
- Small Magellanic
- The Triangullum Galaxy
- Pisces Dwarf
- Aquarius Dwarf
8. What is a cluster?
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- Many local groups of galaxies can be found in gravitational agglomerations called clusters.
- Often there is a giant elliptical galaxy at the centre of a cluster.
- e.g. Virgo Cluster
- 2000 galaxies
- Nearest grouping of galaxies to us
- e.g. fornax Cluster and Coma Cluster
9. What is a super cluster?
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- A group of clusters held together by gravity.
- Our local group and cluster belong to the Virgo Supercluster.
Galaxy < Group < Cluster < SuperCluster < Universe
10. What is an Active Gallactic Nucleus?
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- Region in the centre of some galaxies emitting huge amounts of radiation.
- Not just visible light
- Radio, infra red,UV, X-rays, Gamma rays.
- Supermassive black holes at their centre
- Matter spiralling to black hole emits radiation
11. Name 4 types of active galaxy
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Radio galaxies.
- Seyfert galaxies.
- Quasars
- Quasi -Stellar Radio Source
- Compact
- Extremely bright
- One of brightest objects in universe
- Supermassive black hole at centre.
- One of the oldest objects in universe.
- Discovered 1963
- Blazars
- Emit strongly in all regions of the spectrum.
- Optical brightness can vary over 1 or 2 days.
