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Re: (meteorobs) Geminids 2001 from central Texas USA


> I'm also a little bit puzzled by my limiting magnitude 
> counts versus the seemingly good rates of Geminids that 
> I saw.  I counted star fields over and over but just 
> could not resolve any more stars than I report.  

Ed,

I have a couple of comments. First, it looks like you are using "old" LM tables.  I found them in the IMO's 1989 handbook that I first used, and it noted that the data from the SAO star catalogue, used to compile them, didn't always agree with data from other sources.  We now have more accurate photometry available, and it has been applied to the IMO star fields.  The new table is at: http://www.imodot net/visual/lm.html and uses data from the Tycho catalogue.

From those tables (yes, the two decimal points are absurd, but leave them in until the end of a mean LM calculation):

> 1. Looking roughly RA 7, Dec +16 (right of Jupiter)
> LM, using IMO field #17 (Auriga), 8 stars = +4.6

This comes out as 4.5 on the new table, but the 9th star is 5.2, so it's possible that the LM was as good as 5.1 in this area.  Generally, you should count two or three areas at a time in the general direction that you are viewing. This will allow you to get a better average, or to throw out areas that have big breaks between the faintest visible and brightest invisible stars when you look over your data later.


> 2. Looking roughly RA 7, Dec +20 (below Jupiter)
> LM, using IMO field #4 (Gemini), 7 stars = +5.1

This is listed as 5.3 in the new table, but again the next-brightest star is 5.8.  Apparently, the IMO didn't pay too much attention to LMs under 5.5 when they created the tables (and it's difficult to find an area large enough to include reasonably-spaced bright stars without having a ridiculous amount of faint stars).  Another approach (admittedly a bit labor-intensive) would be to do as the IMO 89 Handbook says and create your own LM tables from data such as AAVSO or from a computer program that uses Tycho photometry.

> 4. Looking at Leo, RA 10:00, Dec +22
> LM, using IMO field #9 (Leo), 9 stars = +5.0

New tables say 5.4 for this one.

> 
> I did not attempt to determine magnitudes.  Maybe some
> night I will.  I feel that if I used more distinctions 
> than "fireball, bright, medium, or faint" I would be 
> making them up.

I guess the best way to get used to magnitude estimations is to start. Yes, your first estimates will be rough, but the more time you spend and the more meteors you see, the better you'll get.

I'm glad that you and others got to see more on Geminid peak night than I did.

--
Wes Stone
http://skytour.homestead.com

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