2. What is the solar system? The Sun, its planets and other objects in orbit are all together known as the solar system.

3. The Sun is the center of our solar system The word “solar” means “of the sun” Our sun is a medium-sized star Our sun is medium-hot, and yellow

4. The sun has layers The middle is called the core – it is 27,000,000 degrees! The outer layer is the chromosphere The layer under the chromosphere is the photosphere, where light and other forms of energy are released Under the photosphere is the convective zone where heat is released The layer above the core is the radiative zone

5. The eight planets (starting with the closest to the Sun) Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune

6. How do these planets move? The Sun is a star which the eight planets move around. The path each planet travels around is called it orbit. The planets are kept in their orbits due to the pulling force of the Suns gravity.

7. Classification of Planets Inner Planets Terrestrial Planets Mercury, Venus, Earth Mars Made mostly of rock and metal Higher densities and very few moons Rotate relatively slowly Smaller in size Outer Planets Gas Giants Jupiter, Saturn, Uranus, Neptune Made mostly of hydrogen and helium gas Lower densities and lots of moons Rotate relatively rapidly Larger in size

8. Mercury is first It has very little atmosphere It has no moons It is VERY HOT!

9. Venus is second It has a very thick atmosphere, and this makes the temperature the highest in the solar system It has no moons It is about the same size as Earth

10. Earth is third It has liquid water It has a medium-thick atmosphere It has one moon It’s where we live

11. Mars is fourth It has a thinner atmosphere than Earth No surface water High winds sometimes Two moons

12. Jupiter, the largest planet, is fifth Jupiter is a gas planet It has rings, and 63 moons The Great Red Spot is a storm that has been there ever since Galileo saw it 400 years ago!

13. Saturn is the sixth planet It is also a gas planet Saturn is famous for its rings, which are easy to see with a telescope – Galileo saw them, too Has 56 moons

14. Uranus is a gas planet, too – all four of the outer planets are It spins sideways, probably because it was hit by a comet or asteroid Uranus has thin rings and 27 moons

15. Neptune is the farthest away It is a gas planet It has VERY strong winds, over 400 miles an hour Neptune has 13 moons

16. What are moons? Moons are ‘natural satellites’ Moons orbit around a planet The moon stays in its orbit due to the gravitational pull of the planet Our moon has a circular orbit We see the moon because it reflects light

17. Pluto is another body now called a dwarf planet It has an irregular orbit – tilted and elongated It has 3 moons – one is very large Eris, the newest body, is also a dwarf planet

18. Objects in space held together by gravity

19. What else is found in our Solar system? Asteroids Meteorites Comets Small rocky bodies that orbit the Sun found in their thousands between Mars and Jupiter in the asteroid belt These are probably fragments of asteroids that broke up These are lumps of ‘dirty ice’ a few km across that travel in highly elliptical orbits. As they near the Sun they warm up. This causes a tail of dust and cloud.

20. There are also: Meteors and comets Space dust Satellites Space junk and trash