Extending the H-R Diagram to More Stars

The H-R diagrams you have made so far cover only stars in the area very close to our Sun - a small part of the whole galaxy. In fact, the volume of space you looked at to make your H-R diagrams of the nearest stars is less than 0.0001% of the volume of our galaxy. Do stars in the rest of the galaxy fall into the same groups as stars close to our Sun? To find out, you need to extend your H-R diagram to include more distant stars.

There is a problem, however. To make an H-R diagram, you need to know the star's luminosity (or absolute magnitude). To find a star's luminosity, you need to know its distance from Earth. But finding the distance to a star is a long and difficult process. Most astronomy projects record only apparent magnitudes, but not distances. To make a convincing H-R diagram, you need to make sure the data you use includes some measure of the distance to stars.

The most effective way to determine the distance to nearby stars is to measure the star's parallax. Click Next to learn more about parallax, and how it is measured.