Stars and planets

• What is a light year?

  One light year is the distance light travels in 1 year
• What does 1 light year equal?


  9460000000000km
• What does gravity provide?

  Centripetal force needed to keep objects in orbit
• What is a galaxy?

  Composed of hundreds of millions stars each orbiting the galaxies' centre of mass. Centre of mass is thought to be a supermassive black hole.