SUN, EARTH, MOON

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POSITION Sun is 150 million km from Earth Moon is (on average) 384,000 km from Earth

SIZE The sun’s diameter is 100 times greater than Earth’s diameter The moon’s diameter is 27% of Earth’s diameter

THE SUN Nearest star to Earth (1 of 100 billion just in the Milky Way) Ball of hot gas powered by nuclear fusion (nuclei of atoms colliding and fusing together) 15,000,000°C at its core and 5,500°C at its surface Small amount of that energy reaches Earth’s surface as light and thermal energy The other planets in our solar system (including Earth) revolve around the sun

Earth’s Orbit Orbit: the path an object follows as it moves around another object Revolution: the motion of one object around another object Earth’s orbit around the sun is nearly circular One complete revolution around the sun takes ______ days (leap year) http://ed.ted.com/featured/GTxsh2IC

WHY DOES THE EARTH ORBIT THE SUN? The sun’s gravity pulls on Earth, causing the Earth to orbit it The pull of gravity between two objects depends on the mass of the objects and the distance between them The more mass an object has and the closer two objects are to each other, the greater the gravitational pull. IF THE FORCE OF GRAVITY BETWEEN THE SUN AND EARTH WERE TO STOP, THEN EARTH WOULD FLY OFF INTO SPACE IN A STRIAGHT LINE!

Earth’s Rotation Rotation: a spinning motion As Earth revolves around the sun, it rotates (or spins) on its axis (an imaginary line through its center) Earth rotates on its axis in a counterclockwise direction from west to east One complete rotation of Earth takes about 24 hours This rotation helps produce the cycle of night and day Antipoles: http://www.findlatitudeandlongitude.com/antipode-map/#.V9gaAI- cHIU

Sun’s Apparent Motion It appears the sun is moving from east to west across the sky from Earth It is Earth’s rotation that causes the Sun’s apparent motion The moon and stars also appear to move from east to west across the sky

Moon The moon does not emit its own light! You only see the moon because light from the sun reflects off the moon and into your eyes. Time for one rotation: 27.3 days Time for one revolution around Earth: 27.3 days

The Moon’s Formation Giant Impact Hypothesis: Shortly after Earth formed 4.6 billion years ago, an object about the size of Mars collided with Earth. The impact ejected vaporized rock that formed a ring around Earth Eventually, the material in the ring cooled and clumped together and formed the moon https://www.youtube.com/watch?v=c0FCE4H0Dro

The Moon’s Surface Craters: formed when objects crashed into the moon more than 3.5 billion years ago Maria: formed when lava flowed up through the crust and solidified Highlands: light-colored areas where lava could not reach https://www.youtube.com/watch?v=UIKmSQqp8wY

What if the Earth stopped spinning? http://ed.ted.com/featured/3zhrMlKw