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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

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lecture 34 galaxies and the universe
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

These are the closest galaxies

Question: How do we know their distances?

our galactic neighborhood the local group

Our Galactic Neighborhood- The Local Group

Galaxies come in clusters, too

A new unit, the Megaparsec

beyond the local group
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

Types of Galaxies

Spirals, Ellipticals, Irregulars

the virgo cluster
The Virgo Cluster
  • Distance ~ 20 Megaparsecs
  • > 1000 galaxies
  • Largest are giant ellipticals like M87
not the end of the story the abell clusters
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
now the question how can you know the distances to these objects

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
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?
the hubble relation for galaxies
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 galaxies1

The Hubble Relation for Galaxies

If you measure the redshift, you know the distance

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