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Lecture 34 – Galaxies and the Universe. Repeatedly said there are other galaxies. Now details Large Magellanic Cloud (satellite to Milky Way) . Distance=50 kpc. Pic: http://antwrp.gsfc.nasa.gov/apod/ap010804.html M31: Distance=730 kpc, Pic: http://antwrp.gsfc.nasa.gov/apod/ap021021.html - PowerPoint PPT Presentation
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Lecture 34 – Galaxies and the Universe
• Repeatedly said there are other galaxies. Now details
• Large Magellanic Cloud (satellite to Milky Way) . Distance=50 kpc. Pic:http://antwrp.gsfc.nasa.gov/apod/ap010804.html
• M31: Distance=730 kpc, Pic:http://antwrp.gsfc.nasa.gov/apod/ap021021.html
• M33: Distance = 670 kpc, Pic: http://antwrp.gsfc.nasa.gov/apod/ap030924.html
These are the closest galaxies
Question: How do we know their distances?
Our Galactic Neighborhood- The Local Group
Galaxies come in clusters, too
A new unit, the Megaparsec
Beyond the Local Group
• Other small groups of galaxies
• Typical spacing of a few Megaparsecs
• Our “neighbors” include some of the brightest binocular galaxies
• See Appendix 15 for list
Types of Galaxies
Spirals, Ellipticals, Irregulars
The Larger Neighborhood
The Virgo Cluster
• Distance ~ 20 Megaparsecs
• > 1000 galaxies
• Largest are giant ellipticals like M87
Not the end of the story: the Abell clusters
• Published in 1958
• 2718 “Rich Clusters” like the Virgo cluster
• Most distant 2 billion light years
The Abell Clusters
Now the question: how can you know the distances to these objects?
You can’t see Cepheids that far out
Turn to one of Hubble’s greatest discoveries
• He discovered galaxies as “island universes”
• Measured distances to galaxies
• Measured velocities (toward us or away)
• How?
Illustration of a galactic redshift
The Hubble Relation for Galaxies
• Galaxies in all directions receding from us
• The more distant they are, the faster they are receding
• v=H0d
• v = speed of recession (km/sec), d= distance (Mpc), H0 “Hubble Constant”, (km/sec/Mpc), H0 = 70 km/sec/Mpc
The Hubble Relation for Galaxies
If you measure the redshift, you know the distance
With measurements of distances, you can map out the distribution of galaxies