If we have a well-calibrated main sequence, we can use it to get distances to distant star clusters.
| Remember that star spend most of
their lives on
the main sequence.
If we have a well-calibrated main sequence, we can use it to get distances to distant star clusters. |
|
Remember the Hertzprung-Russell
diagram for star clusters:
 |
Clusters |
 |
 |
|
 |
If we measure an HR diagram using apparent magnitude
for
clusters of unknown distance, and compare it to a calibrated
HR diagram
(which has absolute magnitude), we can get the distance
modulus of the cluster (m-M) which gives us the distance.
(m-M=5log(d)-5,
right?)