# H-R Diagram Star Cluster

1. Mar 3, 2014

### bobo1455

Here's the question:

The following ﬁgure is the H-R diagram of a star cluster. Use this diagram to determine the age of the cluster.

(A) 600 thousand years
(B) 6 million years
(C) 60 million years
(D) 600 million years
(E) 6 billion years

Here's my attempt:

I know that to determine the age of the cluster, we need to start by determining where in the graph the stars start changing from main sequence. And at that point, we find on the horizontal axis one of the following: OBAFGKM

And then the letter has 10 sub-groups, so I believe the classification to be G2 or G1. This is the part I'm stuck on, if it is G1 or G2 (or pretty much any sub-group of G in general), how do I get the age?

I read in my textbook that G1 is about the age of the Sun, but all of the multiple choice answers are 6-something and I don't understand how to get that, or at least something close to that.

I determined the answer to be 10^10, which is 10 billion, I believe. But it's really off and completely wrong.

2. Mar 6, 2014

### Novareon

AST201 UTM? :D

The best way to figure out this question is to look at the diagrams + text on p.326-27 and compare the cluster to the examples given. Finding the Main sequence turnoff point and reading up on the 'general' lifetimes of specific classes of stars given on these two pages as well will go a long way in helping to determine the most appropriate answer. GLHF

3. Mar 6, 2014

### bobo1455

yeah, I figured it out. You go to UTM too?

4. Mar 6, 2014

yeah lol

5. Mar 6, 2014

### BvU

Hey you guys, 100 people have already looked at this thread in the hope to either be able to help or to learn something. And all you can utter is OBAFGKM, AST201 UTM? GLHF !​

And the only stuff left on the public part of the site is the 2009intro and the syllabus. But I could just about dig up a book The Cosmic Perspective, 5th edition, by Bennet, Donahue, Schneider and Voit which might have a p326-327 with diagrams+text. Right ? Or am I barking up the wrong UTM ?

BvU

6. Mar 6, 2014

### bobo1455

We're talking about University of Toronto Mississauga lol

BvU are you attending UTM too? this is hilarious

7. Mar 6, 2014

### BvU

BvU is in GMT+1 and it's bedtime there. You guys amuse yourself, Ok, but try to make this thread somewhat more informative for others, pls!

8. Mar 6, 2014

### bobo1455

Well I don't want to just give the answer away

I've already given so much information

9. Mar 6, 2014

### BvU

:tongue:

10. Mar 6, 2014

### Novareon

BvU, You seem confused that the information mentioned exists only in the specifically mentioned source, but it just so happens to be be highly relevant in this situation and to the OP.

The idea of finding the main sequence turnoff point and reading up on the 'general' lifetimes of specific classes of stars (O,B,A,F,G,K & M) is extremely helpful towards solving this problem.