How do we know anything at all about space?

No one has ever travelled beyond our cosmic back yard, so all we really have to go off is the tiny drizzles of light that hit our telescope

The Andromeda Galaxy weighs 800 billion times the mass of the sun. The Galaxy M51 is 26 million light years from earth. The Pleiades are between 75 and 150 million years old. These are all “facts” about space, but how do we know any of them? No one has ever travelled beyond our cosmic back yard, so all we really have to go off is the tiny drizzles of light that hit our telescopes. In this talk Dr. Ciaran Fairhurst will devote some time looking at how the sausage is made, and just how hard it is to assemble anything that looks like knowledge about space.