Estimate Limiting Magnitude

Estimate Limiting Magnitude on Monthly Skywatch on Jan 17, 2015.

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Here is simple method of estimating the visual limiting magnitude by counting stars.  This method is in use by the International Meteor Organization (IMO) for several years now.  This method involves in counting stars within certain area of sky marked by stars. There method  IMO has identified 30 fields

For the 17th Jan Skywatch most useful IMO star fields are #4 and #8.

Field #4 has α Geminorum (Castor)  – ε Geminorum (Mebsuta) and β Geminorum (Pollux)

Field #8 has  α Tauri (Aldebaran) – β Tauri (Elnath) and ζTauri

(to help you identify the star map is given below)

All you have to do is to first identify the three stars in each group and then count the number of stars (including the corner stars).  The table given here give the limiting magnitude for number of stars counted by you.

Please note, the limiting magnitude is an observer specific quantity. Do not be surprised if other observers at the same site obtain different limiting magnitudes to you. This is the rule, rather than the exception. Only record your own values! There are several methods for determining the limiting magnitude.

Please record the following information

Your name:… …… ……

Age:………………  ; your location:……………………….

Observing time:………………………
Star field # ………….    Number of stars counted ……………. lm ………..

Observing time:………………………
Star field # ………….    Number of stars counted ……………. lm ………..

Observing time:………………………
Star field # ………….    Number of stars counted ……………. lm ………..

——   ——

Table to estimate the limiting magnitude

   #4 Gemini      #8 Taurus
 N        lm           lm
 1	 1.22         0.99
 2	 2.02         1.68
 3	 3.01         3.00
 4	 3.79         4.62
 5	 5.01         4.88 
  
 6	 5.07         4.95
 7	 5.34         5.09
 8	 5.75         5.29
 9	 5.76         5.43
 10	 5.78         5.51

 11	 6.20         5.73
 12	 6.37         5.84
 13	 6.47         6.10
 14	 6.54         6.19
 15	 6.67         6.27

 16	 6.76         6.29
 17	 6.80         6.36
 18	 6.99         6.50
 19	 7.00         6.55
 20	 7.02         6.71

 21	 7.10         6.76
 22	 7.12         6.77
 23	 7.17         6.87
 24	 7.22         6.88
 25	 7.43         6.95

 26	 7.45         7.15
 27	 7.46         7.17
 28	 7.46         7.19
 29	 7.47         7.21
 

you may refer to this star map

field 4 and 8 copyfield 4 and 8 copy

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