1. Overview for Estimating Age of Star Clusters
Look for a turn-off point from Main Sequence
Determine spectral class of stars at turn-off point
Estimate lifetime of this spectral class (see table next page)
Use spectral class lifetime as estimated age of star cluster
Sidebar
If there is no turn-off point from Main Sequence it must be very young cluster
No cluster can be older than the universe, which is ~13.7 billion years old
Main Sequence Region
O B A F G K M

2. Spectral Class ~T ~MS Lifetime
=========== ========== ==========
O 30,000 K 10 million years
B 20,000 K 100 million years
A 10,000 K 1 billion years
F 8,000 K 5 billion years
G 6,000 K 10 billion years
K 5,000 K 25 billion years
M 3,000 K >100 billion years