Welcome to the Milky Way Galaxy Galaxies A

Welcome to the Milky Way Galaxy

Galaxies • A galaxy is a “system of millions or billions of stars, together with dust and gas, held together by gravitational attraction. ” • There are 3 types of galaxies: Elliptical, Spiral, and Irregular • • Elliptical galaxies are elongated spheres Spiral galaxies have a spherical shape in the center with arms spiraling out Both Elliptical and Spiral galaxies have further classifications Irregular galaxies have no regular shape to them • According to astronomers, their best estimate predicts there at least 100 billion galaxies in the observable universe.

Elliptical Galaxy (NGC-1316; 62 million light years away)

Spiral Galaxy (M 83, otherwise known as the Southern Pinwheel Galaxy; 15 million light years away)

Irregular Galaxy (NGC-1569; 8, 000 light years across; 11 million light years away; considered a very close and young galaxy)

Milky Way Galaxy • This is an artist’s conception of what the Milky Way Galaxy looks like. The artist based the picture on different photos taken by astronomers. • Why don’t we have any real pictures of the Milky Way Galaxy? • Where are we located in this picture?

• We cannot photograph the Milky Way because it is so large, and we are in it. • The Milky Way Galaxy is estimated to be 100, 000 light years across. There approximately 300 billion stars in our galaxy. • That means that it would take light (the fastest speed we know) 100, 000 years to travel across the Galaxy. • Our Sun, and entire Solar System is located within the Orion Arm of the Galaxy. We are a mere dot in our Galaxy. Milky Way Galaxy

Sun Centered Model of the Solar System • Until the year 1543, it was believed that the Earth was the center of our system. • Copernicus and Galileo studied Astronomy and both contributed to what we now know of our Solar System. • The Sun is the center of our Solar System. The moon orbits the Earth and 7 other planets orbit the Sun. • Pluto was a planet for a long time, but is now no longer considered one. • Pluto is no longer considered a planet because of its size, location in space, and tilt of orbit in comparison with the other planets in our Solar System.

Inner Planets • Mercury, Venus, Earth, and Mars are considered the ‘Inner Planets’ • Also known as “Terrestrial Planets, ” which is misleading • Smaller • Either no or few moons • Made of mostly heavy metals, lots of iron and nickel • Solid Surfaces • No rings • Spin slowly compared to outer planets • Orbit the Sun quickly

Mercury

Venus

Earth

Mars

Surface of Mars

Outer Planets • Jupiter, Saturn, Uranus, and Neptune • Also known as the “Gas Giants” • Largest planets • Many moons • Made primarily of gas • All have rings • Spin quickly • Orbit sun slowly

Jupiter • "Jupiter gany" by NASA/JPL - ftp: //nssdcftp. gsfc. nasa. gov/miscellaneous/planetary/voyager/jupiter/vg 1_p 20945. tiff. Licensed under Public Domain via Wikimedia Commons - http: //commons. wikimedia. org/wiki/File: Jupiter_gany. jpg#/media/File: Jupiter_gany. jpg

Saturn

Uranus "Uranus" by NASA/JPL - http: //photojournal. jpl. nasa. gov/catalog/PIA 00032. Licensed under Public Domain via Wikimedia Commons - http: //commons. wikimedia. org/wiki/File: Uranus. jpg#/media/File: Uranus. jpg

Neptune "Neptune" by NASA/JPL - http: //photojournal. jpl. nasa. gov/catalog/PIA 00046. Licensed under Public Domain via Wikimedia Commons - http: //commons. wikimedia. org/wiki/File: Neptune. jpg#/media/File: Neptune. jpg

Asteroid Belt • Separating the inner and outer planets is an asteroid belt.