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? Spiral Galaxy

What is a galaxy made of? Stars Dark Matter Gas Planets Black Holes? Dust

Can you see some of these things? Stars Planets? Gas Dust

There are different types of galaxies Andromeda: Our closest spiral galaxy

Spiral Galaxies have very flat disks

NGC 1365: A Barred Spiral

Elliptical galaxies are the biggest and brightest galaxies Elliptical galaxies are the biggest and brightest galaxies

Most galaxies are spiral, but 30-50% are irregular, funny looking-things Most galaxies are spiral, but 30-50% are irregular, funny looking-things …Kind of like astronomers

Hoag’s Object is an irregular galaxy

This spiral galaxy is warped!

By number, most galaxies are small irregular blobs By number, most galaxies are small irregular blobs

We live in the ‘Milky Way’ galaxy What kind of galaxy is the Milky Way?

It isn’t easy to tell by just looking at it, there is too much dust It isn’t easy to tell by just looking at it, there is too much dust Milky Way in Infra-Red

What the Milky Way might look like if we could get out of it... What the Milky Way might look like if we could get out of it... You 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 (10 11 ) 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 the Milky Way? What are the closest galaxies to the Milky Way? Can you see our closest neighbour in the above picture? Can you see our closest neighbour in the above picture?

There are actually two, the Large and Small Magellanic Clouds. There are actually two, the Large and Small Magellanic Clouds.

The Local Group of Galaxies Most galaxies are very small

Galaxies tend to be clustered in the universe. Galaxies tend to be clustered in the universe.

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

The closest large cluster is the Coma Cluster The 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 ever merged with another galaxy? Do you think the Milky Way has ever merged with another galaxy?

We are currently merging with the Sagittarius Dwarf Galaxy We are currently merging with the Sagittarius Dwarf Galaxy

How Many galaxies are there in the entire universe? How Many galaxies are there in the entire universe?

There are many many galaxies!