The Solar System

1. The Solar System

2. Our Solar System • Although we can not feel it our planet is always moving. Earth moves around the Sun. The planets Mercury, Venus, Mars, Jupiter, Saturn, Uranus and Neptune also move around the Sun. The Sun and all the objects that move around it make up the Solar System. • Each planet in the Solar System moves, or revolves, around the Sun in a path. The path is call an orbit. All the planets travel in the same direction.

3. Our Solar System The force of gravity between the Sun and all the planets keeps each planet in it’s orbit. Without the force of gravity, the planets would fly off into space. A year is the time it takes a planet to make 1 trip or revolution around the Sun. Earth takes 365 days. Other planets take more or less to make 1 resolution. As the planets move around the Sun they also rotate. Each planet rotates around an imaginary straight line called an axis that runs through the planets center

4. Reading Check • What is a revolution? How long is a revolution on Earth?

5. Seasons The tilt of Earth’s axis causes the seasons. The part of Earth tilted away from the Sun is colder than the part tilted toward the Sun.

6. What is the Sun like? • The Sun is the closest star to Earth. A Star is an enormous ball of glowing gas that producers hear and light deep inside it. The temperature if the Sun at it’s center is about 15 million degrees Celsius (about 27 million degrees Fahrenheit.) The sun has been burning for about 5 billion years.

7. THE SUN The Sun is more than 1.3 million kilometers (about 808,000 miles) across. That’s about 260 trips across the United States! This picture shows a large cloud of matter erupting from the Sun. The light areas shown on the Sun are hotter places. The dark areas are cooler places.

8. Reading check • How many stars are in our solar system? What is the name of the closest star in our solar system?

9. The Inner Planets • Mercury, Venus, Earth, and Mars are the 4 planets closets to the Sun. They are called the inner planets. Their surfaces are hard and rocky with bowl-shaped holes called craters. The craters formed when objects from space hit the planets. Some of the planets have moons, rocky objects that revolve around them.

10. Mercury Diameter: 4,878 km (3,031 miles) Surface: Rocky with craters, high cliffs, and smooth plains Moons: 0 Length of the day: 58.6 Earth days Length of a year: 88 Earth days

11. Mercury • Mercury is the smallest of the inner planets. It is less than half the size of Earth. Mercury is the planet nearest to the Sun. Sometimes we can see Mercury for a short time after sunset or before sunrise but not in the middle of the night. • Mercury has no atmosphere or gases around it. During the day Mercury gets hotter than the hottest desert and at night colder than the Earths poles.

12. Reading Check • How many Earth days is a length of year on Mercury?

13. Venus • Venus is sometimes called Earths twin. They are about the same size. • Venus rotates in the opposite directions from most other planets. It’s axis spins from East to West or clockwise. Venus rotates slowly that a day on Venus is longer than a year on Venus. • It’s atmosphere is mostly carbon dioxide gas. Venus’s atmosphere traps lots of heat from the Sun. This makes Venus the hottest planet. • Very thick clouds are always swirling around Venus. The thick clouds make it hard to study from Earth.

14. Venus Diameter: 12, 104km (7,521 miles) Surface: Smooth plains, huge hills, volcanoes, and craters. Moons: 0 Length of day: 243 Earth days Length of year: 224.7 Earth days.

15. Reading Check • Why is Venus the hottest planet in our solar system?

16. Earth • Earth is the largest of the 4 inner planets. Sometimes it is called the water planet. That is because water covers more than two-thirds of it’s surface. Earth’s surface is a rocky crust with plains, mountains, volcanoes, and craters. Some of Earth’s tallest mountains are under the oceans. Earth’s atmosphere contains mostly nitrogen and some oxygen to breathe. Earth is the only planet known to have the atmosphere, water and temperature that living things need. • One day is the time it takes Earth to make 1 rotation. As Earth rotates the part that faces toward the Sun has daytime. The part that faces away from the Sun has nighttime.

17. Earth Diameter: 12. 756km (7,926 miles) Surface: More than 2/3 covered with water, a rocky crust with plains, mountains, volcanoes, and craters. Moons: 1 Length of day: 23 hours and 56 minutes Length of year: 365.25 days

18. Reading Check • What gases are in Earth’s atmosphere?

19. Our Moon The moon is the Earth’s closest neighbor in space. The moon rotates on an axis. The moon revolves around Earth, so it is Earth’s natural satellite. The Moon’s surface is covered with rocks and dust. There are plains mountains, valleys and many craters. The moon has no air. The diameter of the moon is about ¼ the diameter of Earth. The moon gives off no light of it’s own. We can see the Moon because the Sun’s light reflects off it. As the Moon rotates, the part of the Moon facing toward the Sun is lighted. The part of the Moon facing away from the Sun is dark. As the Moon revolves around Earth, we can see different amounts of its lighted surface. Because of this the Moon’s shape seems to change from day to day. We call these shapes the phases of the Moon. There are 8 phases from new moon to full moon to full moon and back to new moon. This cycle takes about 29 days and 12 hours.