Lecture 34 galaxies and the universe
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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

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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 larger neighborhood

The Larger Neighborhood


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


The abell clusters

The Abell Clusters


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?


Illustration of a galactic redshift

Illustration of a galactic redshift


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


With measurements of distances you can map out the distribution of galaxies

With measurements of distances, you can map out the distribution of galaxies


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