Answer the following question about yesterday’s activity at the

bottom of page 21• Explain how you decided how many

groups of galaxies you would have. What physical properties did you use to identify your groups?

What is this?What is this?

Spiral GalaxySpiral Galaxy

What is a galaxy made of?What is a galaxy made of?

StarsStars

Dark MatterDark MatterGasGas

PlanetsPlanets

Black Holes?Black Holes?DustDust

Can you see some of these things?Can you see some of these things?

StarsStars

Planets?Planets?

GasGas

DustDust

There are different types of galaxiesThere are different types of galaxies

Andromeda: Our closest spiral galaxyAndromeda: Our closest spiral galaxy

Spiral Galaxies have very flat disksSpiral Galaxies have very flat disks

NGC 1365: A Barred SpiralNGC 1365: A Barred Spiral

Elliptical galaxiesare the biggestand brightest galaxies

Elliptical galaxiesare the biggestand brightest galaxies

Most galaxies are spiral, but 30-50%are irregular, funny looking-thingsMost galaxies are spiral, but 30-50%are irregular, funny looking-things

…Kind of like astronomers…Kind of like astronomers

Hoag’s Object is an irregular galaxyHoag’s Object is an irregular galaxy

This spiral galaxy is warped!This spiral galaxy is warped!

By number, most galaxies are smallirregular blobsBy number, most galaxies are smallirregular blobs

We live in the ‘Milky Way’ galaxyWe live in the ‘Milky Way’ galaxy

What kind of galaxy is the Milky Way?What kind of galaxy is the Milky Way?

It isn’t easy to tell by just looking at it,there is too much dustIt isn’t easy to tell by just looking at it,there is too much dust

Milky Way in Infra-RedMilky Way in Infra-Red

What the Milky Way might looklike if we could get out of it...What the Milky Way might looklike if we could get out of it...

You are hereYou are here

Distances in space

• Astronomical Unit (AU): Distance from sun to Earth = 149,598,000 km

• Light year (ly): distance light travels in one year = 9,460,730,472,580.8 km

• Parsec = 3.26 light years

OUR GALAXY• Our solar system resides in the Milky Way Galaxy, a

system containing about 100 billion (1011) stars.• Our Galaxy is about 30,000 parsecs (100,000 light years) in

diameter, and our solar system is about 10,000 parsecs from its center.• To put this in perspective: the space shuttle travels at

7.86km/s in orbit. If it was able to maintain that speed, it would take it 3,733,000,000 years to get to the other side of our galaxy (or 186,639,850 generations of humans (assuming they reproduce when they are 20 years old))

•Our Galaxy is of the type known as a spiral galaxy, with a flat disk-like shape, thicker at the center than at the edges.•The density of stars increases toward the center of the Galaxy, and also toward the plane of the Galaxy.•The fact that we see many more stars when we view in the plane of our galaxy than in directions perpendicular to the plane is responsible for what we call the “milky way”- a band around the sky that appears (to the unaided eye) to have a faint, diffuse glow.•The solar system revolves around the center of the Galaxy, once every 200 million years.•Our Galaxy is only one of perhaps 100 billion galaxies which make up the entire observable Universe.

What are the closest galaxies to theMilky Way? What are the closest galaxies to theMilky Way?

Can you see our closest neighbour inthe above picture?Can you see our closest neighbour inthe above picture?

There are actually two, the Large andSmall Magellanic Clouds.There are actually two, the Large andSmall Magellanic Clouds.

The Local Group of Galaxies

Most galaxiesare verysmall

Galaxies tend tobe clustered inthe universe.

Galaxies tend tobe clustered inthe universe.

There are rare, massive clusters of galaxies, like Abell 2218There are rare, massive clusters of galaxies, like Abell 2218

The closest large cluster is the Coma ClusterThe closest large cluster is the Coma Cluster

Galaxies can merge together

‘The Mice’ are an example of merging galaxies‘The Mice’ are an example of merging galaxies

Do you think the Milky Way has evermerged with another galaxy?Do you think the Milky Way has evermerged with another galaxy?

We are currently merging with theSagittarius Dwarf GalaxyWe are currently merging with theSagittarius Dwarf Galaxy

How Many galaxies are there in theentire universe?How Many galaxies are there in theentire universe?

There are many many galaxies!There are many many galaxies!