M 13

I recently had the enjoyment of attending the BFSP. I noticed that the views were not nearly as bright as they were last year, when I was there in August. The view of M 13 last year looked very bright, each star very bright whereas this year they were not nearly as bright, what are the probable reasons for this?

Probably "transparency", meaning there may have been more water vapor or thin clouds this year. The Clear Sky Clock includes a transparency prediction. You can have high thin clouds that would be visible during the day but not noticeable at night.

Another possibility is that you were more in the sunshine during the day this year, that may have hurt your own night vision. Or maybe alcohol? 8)

PS, I assume you mean through similar size telescopes. Aperature makes a huge difference for globular clusters like M13.

Mike

I'm going to agree and say that the transparency of the sky was worse. If it was humid, you may have been looking through some nasty air.

Gee, I dunno, Jim. I was there also, and on Friday night (at least early) I was seeing 16th magnitude stars in my 13" - I've never been able to do that before. Saturday night the transparency was not as good. What night are you referring to? Last year's BFSP was late August, and I remember poor transparency, but steady, which was perfect for Mars observations. Friday night's transparency was way better than last year's.

But admittedly there was a lot of moisture this year, in the form of dew. And in the wee hours of Saturday morning, everyone's mirrors, including primaries, were fogging up due to ground fog. The field was just too wet from the several inches of rain Frances dropped on it Wednesday. Perhaps you had the start of some dewing problems and you didn't realize it?

Best regards,
Doug