7 th Grade Science Ms. Fauss

Earth centered Early Greek scientists believed in this model Planets, Sun, Moon were fixed in separate spheres that rotated around Earth Included Earth, the Moon, the Sun, five planets (Mercury, Venus, Mars, Jupiter, and Saturn), and the sphere of stars

 Heliocentric Model  Published by Nicholas Copernicus in 1543  States that the moon revolves around the Earth  Earth and other planets revolve around the Sun  Daily movement of the planets and the stars is caused by Earth’s rotation

 The Sun’s gravity holds the planets and other objects in the solar system in their orbits.

 Clues found by astronomers through careful observations:  More than 4.6 billion years ago, the solar system was a cloud fragment of gas, ice, and dust.  The cloud fragment became a large, tightly packed, spinning disk.  The center of the spinning disk was so hot and dense that nuclear fusion reactions began to occur and the Sun was born.

 Eventually, the rest of the materials in the disk cooled enough to clump into scattered solids.  Finally, these clumps collided and combined to become the planets that make up the solar system we know today.

 Theories regarding how our moon may have formed:  It was captured by Earths’ gravity  It condensed from the same cloud (the one that formed the solar system) of dust and gas  Earth ejected molten material that became the moon  *Impact Theory: It formed billions of years ago from condensed gas and debris that was thrown off from a collision between Earth and a Mars sized object.

 Inner Planets:  Mercury, Venus, Earth, Mars ▪ Small, rocky planets with iron cores Outer Planets: –Jupiter, Saturn, Uranus, Neptune, (Pluto) –These planets, except Pluto, are much larger and are made mostly of lighter substances such as hydrogen, helium, methane, and ammonia Pluto: –Only outer planet (dwarf planet) made mostly of rock and ice

 Nicholas Copernicus thought that the planet orbited the Sun in circles.  In the early 1600s, German mathematician Johannes Kepler discovered that the shapes of the orbits are not circular, but oval, or elliptical.

 Discovered that the planets travel at different speeds in their orbits.  Planets closer to the Sun travel faster than planets farther away from the Sun.  Outer planets take much longer to orbit the sun. Why? ▪ Farther away from Sun ▪ Slower speed