Kepler's Laws

Aimed at pupils aged 14-18, this activity will focus on investigating Kepler's three laws of planetary motion, with a particular emphasis on Kepler's Third Law: The Law of Periods, which explains the relationship between the distance from an orbiting body to a system's centre of mass and its period of orbit.

Pupils 16-18 / more able students: The relationship will also be put to the test by calculating the mass of the host star of the stellar system TRAPPIST-1 using the known orbital periods of its exoplanets. 

Centre of Mass

Earth and Moon taken by
the Galileo Spacecraft
Credit: NASA
Mass is the amount of "stuff", or matter, and object has and this amount remains the same wherever the object is, even though it's weight will change depending upon gravity.

Phases of the Moon

It takes the Moon around 27 days to orbit around the Earth, during this time we see the Moon go through a series of different shapes, known as the "phases" of the Moon. It takes around 29.5 days for the Moon to get back to exactly the same phase, this is a little longer than it takes it orbit the Earth, due to the fact that the Earth is also moving around the Sun at the same time.