THE EARTH AND THE SOLAR SYSTEM

1. THE EARTH AND THE SOLAR SYSTEM UNIT 7

3. THE EARTH AND THE MOON The Earth is tilted on its axis. The moon is about four times smaller than the Earth. It’s the Earth’s only natural satellite. The moon orbits the Earth and takes about 28 days and the same time to complete one rotation. The moon’s gravity is too weak to have atmosphere. The moon receives light from the Sun and it reflects some sunlight to the Earth. We can only see the illuminated part facing the Earth.

4. Although half of the moon is always illuminated, we can only see the illuminated part facing the Earth. This is why, when we look at the moon on different nights during the lunar month, its shape changes. The different shapes are called the phases of the moon.

5. STARS, CONSTELLATIONS AND GALAXIES • Stars are enormous spheres of gas where nuclear reactions take place. • The nuclear reactions produce light and heat. • Classified by • Colour: blue (hottest and youngest), yellow (Sun), orange, red (coolest) or white. It depends on its temperature. • Size: - smallest stars are smaller than the Earth. • - White dwarfs: very small stars. • - Giant stars: enormous stars. Red giant stars can have a diameter 500 times that of the Sun. • - The Sun is an average star and its diameter is over 100 times the Earth’s diameter. • Luminosity: amount of light from a star that reaches the Earth. It depends on the size, how hot it is and how far it is from the earth. STARS • Constellations are groups of stars. • Great Bear: is named because of its shape. CONSTELLATIONS • Galaxies are enormous systems of stars, dust and gas that are held together by the force of gravity. • They are constantly moving through space. • Sometimes collide and a smaller galaxy becomes part of a larger galaxy. • There are billions of galaxies in the universe. • They are divided into groups by their shape: spiral, elliptical or irregular. GALAXIES MORE

6. Our solar system is part of a spiral galaxy called the Milky way. • - It’s near the end of one of the arms of the galaxy. • - It’s about 30,000 light years away from the centre. • Elliptical galaxies can be round or oval in shape. • - They are the largest. • Irregular galaxies have no real shape. • - They are probably young galaxies where new stars are forming. GALAXIES GALAXIES spiral irregular elliptical

7. Planets in the solar system The solar system is made up of the Sun and the celestial bodies that orbit it. Eight planets orbit the Sun. They orbit in ellipses.

8. Asteroids, comets and meteoroids A S T E RO I D • It’s a rocky, uneven mass that orbit the Sun. • They can be very big or small. The biggest are bigger than a dwarf planet. • Most orbit in the asteroid belt, between Mars and Jupiter. Other beyond Neptune in the Kuiper Belt. • It could hit the Earth but the Jupiter’s gravity holds on the other side of mars. • It’s made of ice, dust and gases. • They come from areas of the solar system beyond Neptune. • They have three parts: • Nucleus is made of frozen water and gases. • Coma is a giant cloud of dust and gases which surrounds the nucleus. • Tail is made of electrically charged gases and dust. It always points away from the Sun. • The coma and tail form when the Sun melts the nucleus. COMET METEOROID • It forms when asteroid collides or breaks up. It’s the burning rock. • The streak of light caused burning rock is called meteor. • Friction caused by air particles rubbing against a meteoroid's surface makes meteor burn. • Meteor showers see when the Earth travels through a stream of ice, dusty debris left by a comet. • Meteorite is a piece of meteoroid that lands on Earth. It can make a large grater.