CHAPTER IX. 
7220 S CYGNI. 
R. A. 20 h 3111 24S.7; Dec. 4 - 57 0 41' 52" (1900). 
This star was discovered at Bonn in i860 and has been well observed, since 
Chandler’s revised elements depend on 43 maxima and 5 minima, but it does 
not appear that the minima have ever been completely followed. Townley 
reports it invisible for two months near minimum in the Madison 15-inch, and 
in the extended series of observations published in Harvard Annals 37 it was 
invisible for periods ranging from 70 to 99 days. The photometric measures of 
comparison stars at Harvard extend only to 13.44, an d those by H. M. Parkhurst 
to 13.48; so that more work was needed in fixing the magnitudes of the fainter 
comparison stars and following the variable through its minimum. In the Har¬ 
vard volume above cited the faintest magnitudes noted before and after minimum 
range from 13.0 to 14.8, and though opportunities for observation when the 
variable was faint have been few, about a dozen comparisons have been made 
when it was below the Harvard limit; and photometric magnitudes have been 
found for the comparison stars down to the faintest used, thus fixing the mini¬ 
mum magnitude of the variable with some precision. 
Table 70.—7220 S Cygni. Standard Magnitude Stars. 
1900. 
Magnitude. 
Residuals. 
Star. 
B. D. No. 
R. A. 
Dec. 
Color, 
P. DM. 
Catalogue. 
Measured. 
From 
Cats. 
3 
Nights 
H.C.O. 
P. DM. 
H. 
P. 
H. 
P. 
inter 
se. 
B 
1 
+ 57 2106 
h m s 
19 56 58 
0 / 
+ 57 32.1 
VV 
7.08 
7-47 
7.29 
7-54 
+ 21 
+ 7 
± 4 
C 
1 57 2129 
20 02 32 
+ 57 19-5 
GW 
7.88 
7.96 
7-53 
7.78 
-35 
-18 
± 6 
D 
+ 57 2144 
20 05 38 
+ 57 29.5 
W 
7.04 
7-32 
7 -i 7 
7.42 
+ 13 
+ 10 
±11 
Mean... 
7-33 
7-58 
7-33 
7-58 
±23 
±12 
± 7 
Table 71.—Comparison Stars in B. D. Catalogue. 
Star. 
B. D. 
1855. 
Star. 
B. D. 
1855- 
No. 
Mag. 
R. A. 
Dec. 
No. 
Mag. 
R. A. 
Dec. 
O 
h m s 
O / 
C 
h m s 
0 / 
c 
+ 57 2124 
8-9 
20 00 23 
+ 57 23.9 
T 
+ 57 2137 
9.0 
20 2 44 
+ 57 30.3 
d 
4-57 2128 
9.0 
20 1 18 
+ 57 36.0 
g 
+ 57 2139 
9-5 
20 3 20 
+ 57 29.0 
e 
+ 57 2130 
9-3 
20 2 4 
+ 57 31-6 
b 
+ 57 2149 
8.1 
20 6 2 
+ 57 53-6 
f 
+ 57 2135 
8-9 
20 2 29 
+ 57 35 -i 
117 
