16 Sidereal Explorations
It is clear from Figures 11 and 12, with the addition of
Figure 6, that the number of Class A stars increases with
decreasing brightness at different rates in different parts of
the sky. In heavily nebulous regions the increase is slow;
in transparent regions where the remote A stars are not lost
by intervening nebulosity the increase is rapid. I have
selected five different areas in the Taurus region for which
the frequency curves are tabulated in Table III and plotted
Table III
Number of Class A Stars Per Square Degree
in Taurus
|
Area |
Number of |
Photographic Magnitude | |||||
|
6-7 |
7-8 |
8-9 |
9-10 |
IO-II |
11-12 | ||
|
I |
35 |
O. I |
0.2 |
0.2 |
o∙ 5 |
I.O |
1∙3 |
|
2 |
99 |
O. I |
0.4 |
I∙3 |
I.O |
1.8 |
0.8 |
|
3 |
5° |
O. I |
o∙5 |
i∙3 |
2.8 |
4∙7 |
... |
|
4 |
75 |
0.2 |
θ∙3 |
i∙5 |
3-6 |
7-5 | |
|
5 |
62 |
0.2 |
0.3 |
i∙7 |
4.6 |
12.6 |
... |
in Figure 13. The areas are arranged in order of increasing
richness in stars between magnitudes ten and eleven; Area 1
is the most heavily obscured, Area 5 is nearly if not quite
free of obscuration. Although there is little difference in
the number of Class A stars per square degree brighter than
the eighth magnitude, at the tenth magnitude Area 5 is thir-
teen times as rich as Area 1. Obviously the form of the
frequency curve of apparent magnitude depends on the
area observed.
The average giant star, with a luminosity a hundred times
that of the Sun, is about five thousand light years distant