Things I Used to Know


I was going over old files on a computer I’m reformatting, and I found an astrophysics assignment I wrote in third year:

“An HR Diagram was successfully obtained for both the M34 cluster and part of the NGC188 cluster. The main sequence and red giant branch of M34 is clearly visible, whereas the data for NGC188 appears to encompass only the topmost fraction of the full diagram. M34 and NGC188 appeared to have a main sequence turnoff of approximately 0.0 and 0.7, respectively. From this it was possible to determine that NGC188 is significantly older than M34. Possible outliers in NGC188 were identified by comparing the observed data to a generic HR diagram, and by measuring the rough magnitude shifts between the main sequences of each cluster and an absolute magnitude diagram, the distance moduli were determined. M34 was measured to have a distance modulus of 8.6, and therefore a distance of 5.25×102pc from earth. NGC188 had a distance modulus of 11.4 and a distance of 1.905×103pc. The clusters were found to be roughly 1380 parsecs apart.”

Someone asked me a few weeks ago how to figure out distances like this and I couldn’t remember at all anymore. I wasn’t sure if I had ever even learned it. Apparently I did, I just didn’t learn it very well. But hey, it’s cool that I knew it once! And now I (sort of) know it again.

Here was my photo of NGC188 (in colour!):

NGC188 in colour

My photo of M34:

M34 in colour

  • jason

    Ah yeah, distance moduli. We must’ve taken similar courses; I remember doing that logarithm shit when comparing absolute and apparent magnitudes.

    Also, parsecs are stupid.

    Also, astronomers are stupid for using CGS units. Who really wants energies in ergs and forces in dynes, anyway?

  • Eve

    Without parsecs there would be no way to tell how awesome the Millenium Falcon is. So parsecs will always be needed.