Galaxies

Sombrero galaxy

Arm of the Milky Way

Obj. 1: What is a galaxy? The word Galaxy means “A city of stars” Edwin Hubble is an American astronomer who put galaxies into categories.

Galaxy is a massive collection of stars, gas, and dust kept together Sun’s Stellar Region massive collection of stars, gas, and dust kept together by gravity A stellar region is just a small portion of a galaxy. A galaxy is a massive collection of stars, gas, and dust held together by its own gravity. Galaxies can range in size from 6,000 to 350,000 light-years across. Our own galaxy, the Milky Way, is about 105,000 light-years in diameter. The galaxy pictured here is the Andromeda Galaxy, which is the nearest large galaxy to our own. We think the Milky Way looks very much like Andromeda.

If our solar system was the size of a cell in the human body, our galaxy would still measure over one mile across. Galaxies are enormous in size. This slide shows the scale of our galaxy by analogy to the size of a cell in the human body. [A cell in the human body is about 50 microns (or 0.00005 meters) across.] Using this same analogy, the Andromeda Galaxy would be 22 miles away.

Our Sun belongs to the Milky Way Galaxy- It contains 200 billion stars which are grouped in a flatten disc which bulges in the center. It is about 100,000 light years in diameter

Milky Way

Obj. 2 Describe 4 types of galaxies Edwin Hubble classified galaxies according to their shape (1920-30) Four Classes: Elliptical Spiral Bar Spirals Irregular (no clear shape) Biggest Galaxies: Super Giant Elliptical= 3 million Light years Smallest Galaxies: DwarfElliptical= 1000 Light years

Spiral galaxy- It is a flatten disc with spiral arms. There is a galactic bulge in the center that is thick and bright. Two or more arms wind out from the center of the galaxy. The Milky Way is a spiral galaxy.

Example of a spiral galaxy

The Andromeda galaxy is our nearest neighboring galaxy The Andromeda galaxy is our nearest neighboring galaxy. It is a spiral galaxy. Hubble telescope has revealed that it has 2 nuclei which means at one point it has eaten a smaller galaxy

Andromeda Galaxy

2. Barred spirals- they differ from spiral because of an elongated bar of matter that the arms extend from

The bar in this galaxy extends 150,000 light years across the center The bar in this galaxy extends 150,000 light years across the center. The light we see from this galaxy took 75 million light years to reach Earth…left at the time of the dinosaurs

3. Elliptical galaxy- Has no spiral arms or shape 3. Elliptical galaxy- Has no spiral arms or shape. They range in shape from elongated to circular. Some contain trillion of stars.

Sombrero- famous ellipitical galaxy-it is shaped like a hat…because of its shape, some scientist think it has a black hole in the middle

4. Irregular galaxies- very young galaxies which lack regular structure.

Obj. 3: Describe Galaxy clusters and Super clusters Galaxy cluster- A group of galaxies held together by gravity We belong to the local group cluster Super cluster- a cluster of galaxy cluster

Galaxy cluster

Super cluster