5A galaxy is a collection of stars, dust, gas classified by its shape. Spiral has a bulge in the dense center with arms extending outwardElliptical is an egg shape with mostly old starsIrregular lacks definite shapeOur solar system is in the Milky Way galaxy – a spiral galaxy
7The Milky Way Galaxy is a disc about 100,000 light years across and around 2000 light years thick.
8We measure the distance to planets in our solar system in astronomical units or light years The distance from the sun to the Earth is called an Astronomical unit ( AU)1 AU = 93 million miles or 150 million kilometers
9A light year is a measure of distance, not time. It represents how far light will travel in one year.Light travels at about 300 million meters per sec( 3 X m/s) “c”1 light year = 9.5 X metersIt takes light about 5½ hours to travel across the solar system, so a light year is much bigger than this
10Our solar system consists of the sun, eight planets, moons, dwarf planets, the asteroid belt, comets, meteors, and other debris.The sun is the center of our solar systemALL planets, asteroids, and comets orbit the sun.The SUN is our closest star, it is over 100 times the size of the EarthMoons orbit their planets
11Our Sun is a normal main-sequence G2 star, one of more than 100 billion stars in our galaxy. The next nearest star to us (apart from the Sun) is Proxima Centauri, which is about 4¼ light years away. Also known as Alpha Centauri
12A planet is a celestial body that orbits the Sun… 8 or 9?????
13The solar system Solar System Pictures My Very Educated Mother Mercury Venus Earth MarsThe solar systemSolar System PicturesJust Served Us Nine PizzasJupiter Saturn Uranus Neptune Pluto
14The Asteroid BeltAn area of 1000’s of asteroids in an elliptical orbit between Mars and Jupiter.
15The Asteroid Belt separates the inner planets from the outer planets GasparCeres, the largest object in the asteroid beltis a dwarf planetAsteroids that are on a collision course with Earth are called meteoroids.
17This picture shows the sizes of the original three dwarf planets (Pluto, Ceres, and Eris) as compared to Earth. It also shows Pluto's large moon Charon (and its two small moons Nix and Hydra) and Eris's moon Dysnomia to scale. None of the distances between objects in this image are to scale. Images courtesy of NASA
18What happened to Pluto??? READ ONLY: In 2006 the International Astronomical Union (IAU) approved a new classification scheme for planets and smaller objects in our Solar System. Their scheme includes three classes of objects: "small solar system bodies" (including most asteroids and comets), the much larger planets (including Earth, Jupiter, and so on), and the new category of in-between sized "dwarf planets".
19There are currently three official dwarf planets There are currently three official dwarf planets. Pluto, formerly the smallest of the nine "traditional" planets, was demoted to dwarf planet status. Ceres, the largest asteroid in the main asteroid belt between Mars and Jupiter, was also declared a dwarf planet. The third and final (for now!) dwarf planet is Eris, an icy body on the edge of our Solar System that was discovered recently in Eris was temporarily labeled 2003 UB313 when it was first discovered, and given the nickname "Xena", before astronomers settled on the official name of Eris.
20Both planets and dwarf planets orbit the Sun, not other planets (in which case we call them moons). Both must be large enough that their own gravity pulls them into the shapes of spheres; this rules out numerous smaller bodies like most asteroids, many of which have irregular shapes. Planets clear smaller objects out of their orbits by sucking the small bodies into themselves or flinging them out of orbit. Dwarf planets, with their weaker gravities, are unable to clear out their orbits.
21Though there are just three dwarf planets now, their number is expected to grow. Scientists estimate there may be 70 dwarf planets amongst outer solar system objects that have been discovered already. Since we don't know the actual sizes or shapes of many of the objects we've found (because they are so far away), we can't yet determine whether they are actually dwarf planets or not. More observations and better telescopes will help us determine which other objects are dwarf planets. Astronomers speculate that there may be 200 or so dwarf planets out through the distance of the Kuiper Belt, an icy band of frozen planetoids on the edge of our Solar System.