Preliminary use of Google Sky for development of an exercise in familiarization with color magnitude diagrams of open clusters

Google Sky Open Cluster Images (Slightly Processed) and Comments
Open Clusters Images Open Clusters Comments

Please take a look at the following images taken from about 4 - 6 hours of working with Google Sky. Initial thought for me were to maybe provide the students with a template transparency, or a gridded sheet where they can reproduce a rough CMD, or a table with the turn-off colors listed. It'd be great if they knew where these open clusters were located on the celestial sphere; most are not far from the galactic plane.

Color magnitude layer was obtained from:


There were only 5 open clusters that were found that had the R vs G-R photometry available under Google Sky.

The Color Magnitude Layer picks out the 100 brightest stars in the frame and plots them. Thus, as is evident here, even through the graph goes down to R = 21, the 100 brightest stars are all brighter than R = 17 mag.

Google Sky drops in a frame at a given zoom level. Students would have to work with this level in order to minimize field stars, get as deep into the photometry as possible, find the main sequence, turn-off, etc. and yet not exclude many cluster stars.

See the next image.


Messier 35 is perhaps not one of the better ones to work with since it seems to be an extended open cluster. However, here we can discern what appears to be the main sequence and could guess at the turn-off color.

We'd have to correlate G-R turn-off color with cluster age?

M35cmd The best isolated CMD for M 35.

Messier 37 has problems similar to M 35 (there are 4 open clusters all within a small region of the celestial sphere - M35, 36, 37, and 38; only 35 and 37 have the G & R data available).

White lines help guide the eye to the main sequence.

M37cmd The best CMD for M37 (and, that's not great).

This cluster is so pretty!

Here one can definitely see the lower cut-off in R magnitude because of the larger field of view. (By the way, there is a layer that specifies the field of view that we could also download.)

For some clusters, zooming in a bit got rid of too many cluster stars. We should check the optimum zoom level for this cluster. The main sequence and possible the turn-off and sub-giant branch are evident.

It's nice how the G-R index data points are shown in color.

M67cmd Close up of CMD. Is there some of the RGB, or am I imagining it?
M NGC 2158, a good, fairly old open cluster.
NGC2158cmd Nice CMD.

Gorgeous colors!

NGC 2420 is an excellent contrast to NGC 2158, and students could definitely develop the knack in understanding a young cluster's CMD versus a much older one.

NGC2420 Very obvious turn-off and main sequence.