How do astronmers measure distance to stars?
Good question! Stars are _really_ far away, so ordinary techniques of measuring distances (yardsticks, tape measures, echoes) don’t work. There is one truly fundamental method, called “parallax”, another reasonably secure one which is usually called the “Baade-Wesselink” method, and a bunch of indirect methods. I’ll give short descriptions of the two best methods, and some pointers to places you can look for further information. “Parallax” refers to the apparent shift in the position of a nearby object relative to distant objects as the observer moves side-to-side. You can see it for yourself: hold your arm out straight in front of you, and point your thumb upwards. Close your left eye, and, looking with your right eye, line up your thumb with some distant object (a tree, a poster on the far wall of the room, etc.). Now, holding your arm still, close your eye and open your left eye. Look through your left eye at your thumb — and you’ll see that it isn’t lined up with that distant obje
