1. Bell work Look at the photographs of spiral galaxies.
Describe the evidence that indicates that the galaxy is rotating.
What other objects have you seen look similar to a spiral galaxy? Do they rotate?
Record your answers in your science journal.

2. Galaxies

3. Today’s Objectives Identify three types of galaxies.
Describe the contents and characteristics of galaxies.
Explain why looking at distant galaxies reveals what young galaxies looked like.

4. What is a “galaxy”?
A large group of stars outside of our own Milky Way
Made of billions to trillions of stars
Also may have gas and dust
Spiral, or elliptical, or irregular shaped
Information at
NOVEMBER 29, 2007: Resembling festive lights on a holiday wreath, this NASA/ESA Hubble Space Telescope image of the nearby spiral galaxy M74 is an iconic reminder of the impending season. Bright knots of glowing gas light up the spiral arms, indicating a rich environment of star formation. M74 is located roughly 32 million light-years away in the direction of the constellation Pisces, the Fish. The image is a composite of Advanced Camera for Surveys data taken in 2003 and 2005.
Image at

5. Spiral galaxy--Andromeda
Located in the constellation of Andromeda, the Princess, the Andromeda Galaxy is a large spiral galaxy very similar to our own Galaxy, the Milky Way. It is over 65,000 light-years in diameter and approximately 2.2 million light-years in distance. The area shown in this image is quite large on the sky, covering about five times the area of the full Moon.
NOAO/AURA/NSF Images at and

6. Spiral Galaxies
have flat disk, spiral arms, central bulge, and a surrounding halo
some have a “barred” bulge
are fairly large (no dwarf spirals)
have lots of gas and dust and younger stars in their arms, but older stars and little gas or dust in their halos and central bulges

7. Spiral Galaxies
Spiral Galaxies: Circular galaxies that have arms curve outward from a central hub.
Arms are made up of stars and dust

8. More Spiral Galaxies
Barred spiral galaxies: Have two spiral arms extending out.

9. Today’s Objectives Identify three types of galaxies.
Describe the contents and characteristics of galaxies.
Explain why looking at distant galaxies reveals what young galaxies looked like.

10. Elliptical Galaxies
Information on the galaxy on the left at
This image from NASA's Hubble Space Telescope shows the diverse collection of galaxies in the cluster Abell S0740 that is over 450 million light-years away in the direction of the constellation Centaurus.
The giant elliptical ESO 325-G004 looms large at the cluster's center. The galaxy is as massive as 100 billion of our suns. Hubble resolves thousands of globular star clusters orbiting ESO 325-G004. Globular clusters are compact groups of hundreds of thousands of stars that are gravitationally bound together. At the galaxy's distance they appear as pinpoints of light contained within the diffuse halo.
Other fuzzy elliptical galaxies dot the image. Some have evidence of a disk or ring structure that gives them a bow-tie shape. Several spiral galaxies are also present. The starlight in these galaxies is mainly contained in a disk and follows along spiral arms.
This image was created by combining Hubble science observations taken in January 2005 with Hubble Heritage observations taken a year later to form a 3-color composite. The filters that isolate blue, red and infrared light were used with the Advanced Camera for Surveys aboard Hubble.
Information on the galaxy on the right at
JUNE 14, 1995: This Hubble telescope photo mosaic shows a field of distant galaxies.
The brightest object in this picture is NGC 4881 [just above center], an elliptical galaxy in the outskirts of the Coma Cluster, a great cluster of galaxies more than five times farther away than the Virgo Cluster. The distance to the Coma Cluster is an important cosmic yardstick for scaling the overall size of the universe.
Images at and

11. Elliptical galaxies range from spherical to football shaped
range from very small to giant
have very little gas or dust
mostly old stars
similar to the central bulge of a spiral galaxy

12. Elliptical Galaxies -Contain mostly older and dimmer stars.
Elliptical Galaxies: Most common type of galaxy; large three-dimensional football shaped galaxies.
-Contain mostly older and dimmer stars.

13. Today’s Objectives Identify three types of galaxies.
Describe the contents and characteristics of galaxies.
Explain why looking at distant galaxies reveals what young galaxies looked like.

14. Irregular Galaxies
About Image on Left:
MARCH 3, 2005: What happens when a galaxy falls in with the wrong crowd? The irregular galaxy NGC 1427A is a spectacular example of the resulting stellar rumble. Under the gravitational grasp of a large gang of galaxies, called the Fornax cluster, the small bluish galaxy is plunging headlong into the group at 600 kilometers per second or nearly 400 miles per second.
1. IS NGC 1427A ACTIVELY FORMING STARS?
NGC 1427A shows numerous hot, blue stars that have been formed very recently, showing that star formation is occurring extensively throughout the galaxy. Within the Fornax cluster, there is a considerable amount of gas lying between the galaxies. When the gas within NGC 1427A collides with the Fornax gas, it is compressed to the point that it starts to collapse under its own gravity. This leads to formation of the myriad of new stars seen across NGC 1427A. The tidal forces of nearby galaxies in the cluster may also play a role in triggering star formation on such a massive scale.
2. WHAT IS THE EVENTUAL FATE FOR NGC 1427A?
NGC 1427A will not survive long as an identifiable galaxy passing through the cluster. Within the next billion years, it will be completely disrupted, spilling its stars and remaining gas into intergalactic space within the Fornax cluster.
About image on right, From
The glowing gas of the interstellar medium (ISM) is the breeding ground for the formation of new stars, and the cemetery where the ashes of dead stars ultimately return.
A team led by astronomers from the National Optical Astronomy Observatory (NOAO) has conducted a new study called the Magellanic Cloud Emission Line Survey (MCELS) that focused expressly on the ISM in the Large Magellanic Cloud and Small Magellanic Cloud—the nearest major galaxies to the Milky Way.
NASA and NOAO/AURA/NSF Images at , , and

15. Irregular Galaxies any galaxy that isn’t a Spiral or Elliptical
usually have lots of gas and dust and young stars
may have a distorted shape from interaction with another galaxy

16. Irregular Galaxies
Irregular Galaxies: Come in many different shapes and are smaller and less common than elliptical or spiral galaxies.

17. Irregulars….
Small Magellan Cloud (SMC)
Large Magellan Cloud (LMC)

18. The Milky Way
From
Astronomers unveiled today what they are calling the best map ever produced of the Milky Way galaxy.
The new view shows our spiral galaxy as it would look face-on to a very distant observer.
The map is based on findings about the structural evolution of the Milky Way. The researchers determined that the Milky Way actually has two fewer major arms than previously believed. In barred spiral galaxies like our own, major arms have a high density of stars, produce lots of new stars, and are clearly connected to the long bar of stars at the galactic center.
By contrast, minor arms have high gas density and presumably less star formation. Scientists had long thought that the Milky Way has four major arms. But the new images show that the spirals are actually made of two major arms and two minor ones. "These major arms plus the bar could be the things that really stand out if you were looking at the Milky Way galaxy from, say, [our nearest galactic neighbor] Andromeda," Benjamin said.
Image at

19. Our Galaxy: the Milky Way
has about 200 billion stars, and lots of gas and dust
is a barred-spiral (we think)
about 100,000 light-years wide
our Sun is halfway to the edge, revolving at half a million miles per hour around the center of the Galaxy
takes our Solar System about 200 million years to revolve once around our galaxy

20. Today’s Objectives Identify three types of galaxies.
Describe the contents and characteristics of galaxies.
Explain why looking at distant galaxies reveals what young galaxies looked like.