Galaxies What is a galaxy? • A galaxy is a large grouping of stars, gas, and dust in space that are held together by gravity. • The largest galaxies contain more than a trillion stars. Smaller galaxies may have only a few million. • Scientists estimate the number of stars from the size and brightness of the galaxy. Main Types of Spiral Galaxies
Irregular
Elliptical Properties of Spiral Galaxies • Shaped like flattened disks with one or more spiral arms.
• Our galaxy, Milky Way, is a spiral galaxy. • Our solar system is located in one of the spiral arms. Properties of Elliptical Galaxies • About 1/3 of all galaxies. • Simply massive blobs of stars.
• Round or elliptical in shape. • Contain very little gas or dust. • Because of little gas, no new stars are forming. • The largest and smallest galaxies are elliptical galaxies. Properties of Irregular Galaxies • Do not fit into any other category. • Chaotic mix of stars, gas and dust • Usually found near large spiral galaxies who may be distorting their shape. Contents of Galaxies Galaxies are made of stars, planetary systems, gas clouds, and star clusters. Nebulas are giant clouds of Nebula are found gas and dust where in spiral galaxies stars may be but not elliptical forming. galaxies. What is a “nebula”?
• A cloud in space • Made of gas and dust – Can have stars inside • Most of the ones we see are inside our Milky Way Galaxy • Different types
Orion image at http://hubblesite.org/newscenter/archive/releases/2006/01/image/a/resul ts/50/ Galaxy Quiz
A)Spiral
B)Irregular
C)Elliptical Galaxy Quiz
A)Spiral
B)Irregular
C)Elliptical Galaxy Quiz
A)Spiral
B)Irregular
C)Elliptical 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 Milky Way Galaxy Where is our solar system in our galaxy? • The Sun and our solar system is located in one of the outer arms (Orion’s Arm) of the galaxy. The distance from the Sun to the center of the galaxy is about 30,000 light years. • All objects in the galaxy revolve around its center. • The sun and our solar system take about 240 million years to make one trip around the center of our galaxy.
In what Arm of the Milky Way Galaxy is our solar system found?
A)Norma Arm B) Orion Arm C)Perseus Arm D) Sagittarius Arm
Just like our solar system orbits around the sun, in the milky way our solar system is orbiting around….
A) One of the stars B) The Sagittarius Arm C) The center of the galaxy D)It’s not orbiting, that would be crazy…