2.  Earth  Earth is a planet (a celestial body that orbits the sun)  The earth is round because of gravity.  It is the only planet that sustains life.  It is the only planet with large amounts of liquid.  This liquid helps moderate our temperature because it takes a long time to heat and cool.

4.  The sun  The sun is an average size star (1.4 million kilometers in diameter).  That is 330,000 times the mass of the earth.  The sun is brighter than the other stars we see because it is the closest star.  It is so bright during the day we are unable to see the brightness of other stars

6.  It consists of the sun and all of the objects that orbit around it  The sun is the most important part of the solar system and make up 99% of the mass.  The 8 planets and their moons make up the rest.  The solar system also contains dwarf planets, asteroids, comets, dust, and gas.

8.  Every object in the solar system pulls on every other object.  The greater the mass, the larger the gravitational force.  The closer the two objects are the stronger the gravitational force.  The sun exerts the most force because it is the largest.  It keeps the planets in orbit like a ball on a string (elliptical revolutions).  The moons revolve around planets because of the planets gravitational force.

10.  Mercury – rocky, no moons (the closeness to the sun prevented light gases from remaining in the atmosphere)  Venus – rocky, no moons  Earth – rocky, 1 moon  Mars – rocky, few moons or no moons  There is an asteroid belt here (small solar bodies)  Jupiter – gaseous, many moons (this area of space was colder and allowed form a lot of dust and gas)  Saturn – gaseous, many moons  Uranus – gaseous, many moons  Neptune – gaseous, many moons

13.  The first model of the solar system put the earth at the center.  Later, a new model was proposed by Copernicus called the heliocentric theory.  His model of the solar system put the sun at the center. However, he believed planets orbited the earth in perfect circles.  Kepler improved on the model by explaining the planets orbited the sun in ovals, not circles.  Newton finally explained the orbits by explaining gravitational forces (other planets pull on earth as well)

14.  http://members.wri.com/jeffb/visualization/ ss-rotate.shtml. http://members.wri.com/jeffb/visualization/ ss-rotate.shtml  http://neo.jpl.nasa.gov/1950da/animations.ht ml. http://neo.jpl.nasa.gov/1950da/animations.ht ml

15.  Many scientist date the earth at 4.6 billion years old  To explain their belief they proposed the Nebular Hypothesis. It explains why objects that form from a disk will lie in the same plane, have almost circular orbits, and orbit the same direction.  It states that planets formed mostly through the process by which small particles (dust and gas) collide and stick together.  It states that planets formed through the same process.  A nebula is a large clouds of dust and gas in interstellar space; a region in space where stars are born. Hence, then name nebular theory

16.  The sun formed from a large cloud of gas and dust that collapsed on itself do to gravity.  It formed a rotating disk. In the center the material became denser and hotter. A star began to form and spin.  The spinning caused the disk to flatten like a Frisbee. Large particles began to form planets.  The planets grew as their gravity increased. They continued to collect dust and gas.  Small planets collided with smaller. Those particles were collected by the other planets and they grew.  The solar system formed as we know it today.

18.  Watch Birth of a Star.