Finding Your Limiting Magnitude

While gazing and waiting, you'll have plenty of time to find the limiting magnitude in the part of the sky you're watching. The IMO and the North American Meteor Network (NAMN) provide an easy way to do this. They supply charts of various constellations with faint stars labeled. Compare one of these charts with what you see in the sky to find your limiting magnitude. Or just use the chart above of the Little Dipper.

Another approach is to use the chart on the right. Find one of the highlighted areas and count how many stars you can see in it, including the corners. Take a little time and use peripheral vision, but don't push very hard; you want to characterize the ordinary state of your vision during the meteor watch. The table below then tells you the limiting magnitude (LM) that your star count corresponds to.

The limiting magnitude is an essential measure of your light pollution, sky clarity, and night vision. A meteor count is meaningless without it. Taking the average of several limiting-magnitude determinations will reduce random errors. Check again at least once an hour to track subtle changes in sky conditions, always noting the time. Even a small change has a big effect on the number of meteors you see.

Stars per Area of Preceding Chart
Area 3		Area 4		Area 8		Area 9
Beta (b), Theta (q), 23		Alpha (a), Beta (b), Epsilon (e)		Alpha (a), Beta (b), Zeta (z)		Alpha (a), Gamma (g), Delta (d), Beta (b)
UMa		Gem		Tau		Leo
Num.	LM	Num.	LM	Num.	LM	Num.	LM
5	4.5	5	4.3	4	4.7	7	4.4
6	4.6	6	5.0	5	4.8	8	5.0
7	4.8	7	5.1	7	5.1	11	5.6
8	5.2	8	5.3	8	5.3	13	5.7
9	5.4	9	5.6	9	5.5	15	6.0
11	5.7	10	5.7	10	5.9	18	6.1
13	5.8	11	5.9	11	6.0	20	6.3
14	6.0	12	6.1	12	6.1	21	6.4
15	6.1	13	6.2	15	6.2	24	6.6
16	6.2	14	6.3	16	6.3	25	6.7
17	6.3	15	6.4	17	6.4	29	6.9
18	6.4	16	6.5	20	6.5	32	7.0
19	6.5	18	6.6	21	6.6	34	7.1
20	6.6	20	6.7	23	6.7	38	7.2
23	6.7	22	6.9	26	6.8	40	7.3
25	6.8	23	7.0	28	6.9	44	7.4
27	6.9	25	7.2	29	7.0	45	7.5
29	7.0	26	7.3	31	7.4
33	7.1	30	7.5	32	7.5
37	7.2
44	7.3
49	7.4
54	7.5