Harlow Shapley's determination of the size of the Galaxy.
The view based on looking at the stars in the Milky Way:
- Shapley found that globular clusters contained RR Lyrae variables.
- He thought that they were simply Cepheid variables with short periods.
- This assumption gave him their luminosity.
This turned out to be more or less right.
- He measured the distances to globular clusters.
- They were distributed in a spherically symmetric distribution
centered on a point in the plane of the Milky Way, but some distance
from the Sun.
- He argued that this point was the center of the Galaxy.
- His measurement wasn't very good, but a modern estimate
of this distance is 25 Kly.
Davison E. Soper, Institute of Theoretical Science,
University of Oregon, Eugene OR 97403 USA
soper@bovine.uoregon.edu