Graphs

The sea level rises and falls every day. These changes are called tides. Tides happen because of the gravitational pull of the Moon and the Sun on Earth's oceans. The Moon has the strongest effect because it is much closer to Earth. 

The Sun is a constant presence in our life on Earth. It gives us the heat and light we need to survive. But it is not a stable place. The Sun is a ball of hot plasma which is constantly changing.

You have likely heard about the Universe expanding. Or that redshift can tell us about the movements of galaxies. Both are difficult ideas to imagine and understand.