3. Structure of the Solar System Solar System: the sun and the objects that orbit around it Orbit: the path an object takes as it moves around another object in space

4. Solar System has eight planets and the dwarf planet Pluto. Planet: a large body of rock or gas that orbits the sun.

5. Moons are large, rocky objects that orbit planets. Solar system also has:

6. The sun is the center of the solar system. Sunspots: place on sun that is cooler and darker than surrounding material. They generally appear in pairs or groups and have strong magnetic activity.

7. Sun is a star Hot ball of glowing gases Closer to us than other stars Very big – all of the planet and moons of the solar system could fit inside the sun Gravity is very strong - helps hold the objects in the solar system

8. Venus Earth Mars Mercury

9. Mercury, Venus, Earth and Mars are alike in many ways: Closer to the sun – thus are warmer than the outer planets Smaller None of the inner planets has more than 2 moons Earth is different from the rest of inner planets - 1.Has watery surface 2.Only planet with a lot of oxygen in its atmosphere 3.Has plant life and animal life

10. Jupiter Saturn Neptune

11. Outer planets are alike: Made most of frozen gases Very far from sun – so colder than the inner planets Much larger than the inner planets Jupiter is solar system’s largest planet (more than 1,000 times larger than Earth) Most outer planets have many moons Many also have rings of dust and ice around them

12. Asteroid: a chunk of rock or metal that orbits the sun Asteroid Belt between Mars and Jupiter Comet: a large ball of ice and dust that orbits the sun Meteors: chunks of rock from space – come from the asteroid belt

14. The Earth moves in two ways: 1.Earth spins like a top. Rotation is the spinning of an object on its axis. Axis: imaginary line that goes through the North Pole and the South Pole 2. Earth also circles the sun. Revolution: the movement of one object around another object. One revolution takes 1 year.

15. Moon also rotates and revolves. The moon rotates on its axis and revolves around the Earth. One rotation is about 29 Earth Days and the moon takes 29 Earth Days to revolve around Earth.

16. Shadows help us observe Earth’s rotation. In the morning the sun is low in the sky and objects cast long shadows. As the Earth rotates, the sun appears to move higher in the sky and shadows get shorter. At noon, the sun is directly overhead and objects cast very short or no shadows at all.

17. Earth has seasons because its axis is tilted. The tilt changes the way sunlight hits Earth at different times of the year. Part of the year the top of the axis (North Pole) points in direction of the sun. This is summer for the northern half and the bottom of the axis (South Pole) points away from the sun. It is winter in the southern half.

18. Direction Axis Points Season (Northern Hemisphere)Temperature Winteraway from sunCold Spring neither toward nor away warmer than winter from sun colder than summer Summe rtoward sunhot Fall neither toward nor away warmer than winter from sun colder than summer

19. Earth’s rotation causes this difference in time. At any one time, half of Earth is in sunlight. The other half is in darkness. The half in sunlight has day. The half in darkness has night.

20. As the moon moves around Earth, different amounts of its lighted and dark sides face Earth. The moon’s phase depends on the part of the lighted half you can see. Phases are the different shapes the moon seems to have in the sky.

21. The moon goes through all of its phases every 29 ½ days.

22. Earth and moon cast shadows. If you see sun, Earth and moon are in a straight line, Earth blocks some of the sun’s light from falling on the moon. The moon will get dark for a time. Lunar Eclipse: Earth’s shadow falls on the moon

23. Total Lunar Eclipse: causes all of the moon’s face to look dark red. Partial Lunar Eclipse: blocks only part of the sun’s light

24. Solar Eclipse: when the moon’s shadow falls on Earth. This happens when the moon moves between the Earth and the Sun. During a total solar eclipse, the moon blocks out the sun and only a halo of sunlight remains around the moon.