STELLAR PHOTOGRAPHY. 



IS' 



qual to its diameter, and T 



-. We therefore ball have /= a 8V , and as long 

 as the instrument remains unchanged / is proportional to v. If the telescope is at 



mm cos S > 



rest and the motion of the 



due to the rotation of 



and 



fA 



86400 a 2 1 



denoting the decl 



of 



different declinations are 



aphed with th 



same 



by 8. W 



rumen i. 8 



the 



variable 

 and I is 



i of 



un- 



hand member of this equ 



m 



propor 

 5 log / 



the cosine of 



d 



of 



2.5 log G 



2.5 log cos 8. Whe 



we may write /= C cos 8, 



the star. AVe then have 



visli to compare the rela- 

 tive brightness of different stars from the intensities of the trails they leave, this 

 correction must first be applied. The trails must first be reduced to a scale of stellar 

 magnitudes, as will be described later (page 211), and then the correction 2.f» log cos 8 

 added to each. This correction is facilitated by the aid of Table I., which gives for 



every degree of declination the correction in hundredths of a magnitude. 



TABLE I. 



o 



Magn.l 8 



ISIagn 



1 ° 

 20 



Magn 



5 

 1 o 



30 



MagiiJ 



5 



Ma.i, r Ti| S Uagn.l S 

 1 



Mngn. 



0.75 



6 

 o 



70 



1 ° 



0.00 10 



0.02 



0.07 



0.1 o 



o 



40 



0.29 



O 



50 



0.48 



o 



60 



0.00 11 



0.02 1 21 0.07 1 



31 



0.17 



41 



0.31 



51 



0.50 



01 u.7'1 



71 



0.00 12 



0.02 22 



0.08 



32 



0.18 



42 



0.32 



52 



0.53 



02 



0.82 



72 



0.00 13 



0.03 23 0.09 



33 



0.19 



43 



0.34 



•".3 



0.55 



63 



0.86 



73 



0.00 14 



0.03 24 0.10 



34 



0.20 



44 



0.36 



54 0.58 



64 



0.90 



74 



0.00 15 0.04 



25 0.11 



3 5 



0.22 



45 ! 0.38 



55 ! 0.60 



65 0.94 



75 



0.01 16 



0.04 



26 0.12 1 



30 



0.23 



46 0.40 



56 0.63 



66 0.98 76 1 



0.01 17 



0.05 



27 



0.13' 



37 



0.24 



47 



0.42 



57 0.66 



67 1.02177 



0.01 18 



0.05 



28 



0.14 



38 0.26 



48 



0.44 



58 0.69 



68 1.07 78 



0.01 19 



0.06 



29 



0.15 



39 



1 



0.27 



49 



0.46 



59 



0.72 



69 



1.11 



79 



Mngr« 



1.16 



1.2S 



1.40 



1.54 



1.02 



1.71 



1.80 



Ma in i 



1.00 



1.22181 2.01 



•J. 14 



1.34 83 2.29 



2.45 



1.47 85 2.65 



2.89 

 3.20 



3.64 



4.4o 



It is generally sufficiently precise to carry the computations to tenths of a 



In this case, Table II. is more convenient, especially for polar star 



magnitude. 



wh 



ere the correction changes rapidly. The limit- 



of declination within which the 



corrections of each tenth of a magnitude should be applied are given in this table. 

 The correction for any declination given in the table is found by adding the whole 

 number of magnitudes taken from the top of the column to the tenth of a magnitude 



The correction for intermediate declinations is the 



at the beginning of the line. 



same as that of the next smaller declination given in the table. Thus, the correction 



