How & why things go round Gravity and Orbits How & why things go round

The earth’s orbit … Earth Sun … is an ellipse.

Orbits An ellipse is a squashed circle In the solar system, all the planets have elliptical orbits The sun in nearly in the centre of these orbits

Stars The Sun is a star The stars that we see change position in the sky very slowly They are in fixed patterns – constellations The planets move more rapidly across the sky

Planets and Stars The Sun and other stars give out light The planets look like stars to the naked eye Planets reflect light from the sun back to us Light Planet Earth Sun

Comets They have very elliptical orbits The sun is not at the centre of the orbit The ‘tail’ of the comet always points away from the sun Comet and Tail Orbit Sun

Comets As they get closer to the sun the tail increases in size They get brighter as the tail reflects more light They are only visible when close to the sun

Gravity The earth, Sun and moon are attracted by a force called gravity As the distance between bodies increases, the force of gravity decreases rapidly Smaller bodies rotate round larger bodies because they move faster and have smaller mass

Gravity and centripetal force Centripetal force in the direction of travel Gravity – pulls towards the centre