Ah what a fantastic presentation. It answers a lingering question about the use of spectroscopy and apparent brightness to determine the distance to a star. The

Ah what a fantastic presentation. It answers a lingering question about the use of spectroscopy and apparent brightness to determine the distance to a star. The key step that I had missed was using the stars with distances measurable by parallax to calibrate the color/apparent brightness so that it could be used for stars that were beyond the distance for parallax. Obvious in hindsight, but wonderfully and clearly explained here.