Yesterday was the last lecture on cosmology as part of my U3A sessions in Cambridge. We heard some truly staggering numbers which I shall share here.
- There are at least 100000000000 (100 billion) galaxies in the observable universe.
- Each galaxy contains at least 100s of billions of stars.
- The universe is mostly empty space.
- 5% of the universe is atomic matter. The rest is mostly dark matter or dark energy. We do not know what these are.
- Many stars have planetary systems.
- The universe is at least 41 billion light years across.