Photometric versus Nonphotometric nights

[RJN]

I have been tracking Alpha Cas at MK, a known constant star, in an effort to better understand the variability of NSL data. I tracked Alpha Cas on three consecutive nights at MK, 2004 Oct 14, 15, and 16. I took the ratio of data taken on the 14 to 15 and 16. Here is the Excel spreadsheet with the data: http://NightSkyLive.net/temp/mk041016a.xls

The results are summarized by this plot:


Inspection of this plot shows that Oct 16 was clear enough to see Alpha Cas but had some sort of thin clouds visible through most of the night that affected photometry. This caused the change in magnitude between the nights to NOT hover around dM=0 for the second half of the night. Therefore Oct 16 was NOT a photometric night.

In contrast, Oct 15 was not only clear enough to see Alpha Cas but the ratio of the photometric measures over the two nights hovered around zero. This indicates that both Oct. 15 and Oct 14 WERE photometric nights.

Note that both nights showed brief period of high dM which were likely passing clouds.

- RJN

[Vic Muzzin]

1) Maybe we should keep a record of clear nights for quick reference when doing photometry? For example, now that you have done the work to label oct 14 and 15 as photometric nights they should listed to avoid anyone else having to redo your work.

2) Can we apply this to the project of classifying clear nights at each site? It would be fairly easy to take a constant star (or multiple constant stars), gather a month of data, track the deviations each day, and use that to assign a value for observability that night? This could be quick and easy and the best part is that, being based on math, it would eliminate any variances caused by multiple persons doing the analysis.

[Matt Merlo]

I agree with Vic. I think this might be a good way to do the analysis of the sites. It seems to be less subjective than what we were discussing yesterday, though it might be more work. Maybe we should give it a try and see how long it takes us and then decide whether its worth the time and effort.

Matt Merlo

[RJN]

Yes, I agree that it would be good to note photometric nights. I think eventually this can end up in the software, but to start we should just record it here in The Asterisk* Science forum. We just don't have the people power to keep updating the software every few minutes.

I think doing automated differential photometry for a whole year on all the CONCAMs is a great idea but not practical before the January AAS meeting. Also what star is visible for all the CONCAMs all year round? We would have to pick and choose different stars. Again, in my view doable in the long run but time consuming and impractical in the short run. Also, I have found that it helps to do a project preliminarily visually first to get a feel for the difficult parts. This, in turn, helps write the code for the automated analysis.

Next, I looked at the MK movie file for the non-photometric night of Oct 16. Here it is:
http://nightskylive.net/mk/mk041016/movie-mk041016.gif
There are clouds coming in and out much of the night, but there do appear to be some clear times in the middle of the night so it is surprising to me that even these are not photometric.

Next, it seem many times when I play a movie like this, interesting things come out. Here are two cool frames that involve either satellites or meteors. I think I see at least the first one on Haleakala's CONCAM so we should be able to tell the height from parallax between the two stations. The height should tell us if it is a meteor.


The jagged edge does not appear on the FITS frame. If this is a meteor it is perhaps the second most impressive one seen by NSL, the first being our logo earth-grazer seen during the 2001 Leonids.

A few minutes later here is another flash just under Polaris:


- RJN

[lior]

Photometry of one star might sometimes be confusing. For instance, the opacity maps show a big cloud crossing the north part of the sky.

Looking at the set of opacity maps we can see it crossing the sky.

The first meteor picture is not a meteor, but a satelite glint. I didn't compute it percisley, but it is well above the atmosphere. The other one, though, seems like a real meteor.