Question

The first observations that gave us a sense of the true size of our Milky Way Galaxy and the location of the sun in it were those of open clusters.

TRUE OR FALSE?

The first observations that gave us a sense of the true size of our Milky Way Galaxy and the location of the sun in it were those of open clusters. Select one: OTrue False

Answer 1

Solution:

This statement is true.

The discovery of the Galaxy’s true size and our actual location came about largely through the efforts of Harlow Shapley.

In 1917, he was studying RR Lyrae variable stars in globular clusters. By comparing the known intrinsic luminosity of these stars to how bright they appeared, Shapley could calculate how far away they are. (Recall that it is distance that makes the stars look dimmer than they would be “up close,” and that the brightness fades as the distance squared.) Knowing the distance to any star in a cluster then tells us the distance to the cluster itself.

Globular clusters can be found in regions that are free of interstellar dust and so can be seen at very large distances. When Shapley used the distances and directions of 93 globular clusters to map out their positions in space, he found that the clusters are distributed in a spherical volume, which has its center not at the Sun but at a distant point along the Milky Way in the direction of Sagittarius. Shapley then made the bold assumption, verified by many other observations since then, that the point on which the system of globular clusters is centered is also the center of the entire Galaxy.