AIM: The Movement of the Earth Vocabulary: Revolution and Rotation

Model of Solar System

Revolution of the Earth

Revolution Animation

Revolution Animation Notice the Tilt of the Earth: It spins along the Red Line

Gravity and the solar system Gravitational forces between the Sun and planets keep the planets moving in orbit around the Sun. Without these forces, the planets would fly off into deep space. Their orbits are slightly squashed circles called ellipses.

As the planets get further from the Sun: the speed that the planet moves decreases the time to complete an orbit increases

Distance vs. Speed For example, Mercury takes just 88 Earth days to complete an orbit, while Pluto takes 248 Earth years to complete an orbit. The planets furthest from the Sun are also the coldest because they receive the least heat energy from the Sun.

Graph This! Distance vs. Speed PLANET Mercury 100 45000 Venus 200 Speed (m/s) Mercury 100 45000 Venus 200 35000 Earth 300 28000 Mars 400 23000 Jupiter 800 12000 Saturn 1500 10000 Uranus 3000 7500 Neptune 4500 4000 Pluto 5900 Graph This! Distance from the Sun in millions of KM

Distance vs. Speed

YEARS A planet's year is the time taken for it to make one complete orbit around the Sun. The Earth takes 365 Earth days to orbit the Sun. Remember that different planets take different lengths of time to do this the further from the Sun, the slower a planet travels and the longer its orbit takes.

Rotation on its Axis

Days and nights The planets spin as they orbit the Sun. A day is the time taken for a planet to make one complete turn on its axis Different planets take different amounts of time to do this. An Earth day is 24 hours - it takes the Earth 24 hours to make one complete turn on its axis.

Days and nights It is daytime for us when our part of the planet is facing the Sun, and it is night-time for us when our part of the planet is facing away from the Sun. One way to remember which way the Earth turns is to remember "WE spin", which means the Earth spins from west to east.

Days During the day, the Sun appears to move through the sky. Remember that this occurs because the Earth is spinning on its axis. The Sun does not actually move across the sky, it’s the Earth’s Rotation The Sun appears to move from east to west. It 'rises' in the east and 'sets' in the west. At midday we face south to see it.

Days

Night During the night, we cannot see the Sun. But the Earth is still spinning on its axis. This means that the stars appear to move from east to west in the sky, just as the Sun does in the day.

The Sun in the Sky ! When it is summer in the northern hemisphere, it is winter in the southern hemisphere. The Sun appears to be higher in the sky in the summer than it does in the winter.