This is the Milky Way from Concordia Camp, in Pakistan’s Karakoram Range. To the right is Mitre Peak, and to the far left is the beginning of Broad Peak. Photograph by Anne Dirkse, of http://www.annedirkse.com under a c.c.-by-s.a.-4.0 license.

How far away are the stars?

Scientists still don’t know, but the answer could hold the key to the expanding, accelerating Universe.

“Scratch a cynic and you’ll find a disappointed idealist.” -Jon F. Merz

When you look up at the night sky and see the glittering stars overhead, your first thought might be to wonder what, exactly, they are. Once you know they’re very distant suns, however, with different masses, brightnesses, temperatures and colors, your next thought might be to wonder just how far away they are. It might surprise you to learn that despite centuries of advancement in astronomy and astrophysics, from telescopes to cameras to CCDs to observatories in space, we still don’t have a satisfying answer. When you consider that much of our understanding of the Universe today — how it was born, how it came to be the way it is and what it’s made of — is based on the distances to the stars, it highlights just how important this problem is.

Stars that appear to be at the same distance, like the ones in the constellation of Orion, may in fact be many hundreds or even thousands of light years more-or-less distant than one another. Image credit: La bitacora de Galileo, via http://www.bitacoradegalileo.com/2010/02/07/orion-la-catedral-del-cielo/.

If you want to know how fast the Universe is expanding at any point in time, you need to know how fast the distant galaxies are moving away from us and how far away they are. Measuring a galaxy’s…