328 
THE OUTSIDE OF A STAR 
The maximum ordinate of the spectral energy curve occurs near 5900 A. 
Table 43 shows that the intensity is here rising faster than the black- 
body curve as we go towards the violet; hence the maximum ordinate 
will be displaced in this direction. Milne has calculated that the displace 
ment amounts to 4-3 per cent., so that the effective temperature calculated 
from (228-3) is 4-3 per cent, higher than that calculated from the total 
intensity of the radiation. This is actually in good agreement with ob 
servation; but reference to Fig. 5 shows that the accordance is accidental; 
the trivial shift in the position of the maximum ordinate (inappreciable 
on the scale of the diagram) achieves no real advance in explaining the 
sun’s deviation from a black body. 
By (227-2) the contrast in brightness between the centre and the 
selected point near the limb (sec 6 = 3) is 0-6 for the integrated spectrum. 
By Table 43 it is 
iff = 0-46 for A4157; |f| = 0-77 for A12470. 
This is mostly accounted for by the difference of effective temperatures 
5326° and 6039°, a decrease of temperature having more effect on the 
violet than on the red. According to Milne the observed contrast in all 
wave-lengths agrees very closely with that predicted by this theory. He 
considers this agreement to be very unwelcome; it is premature because 
we have yet to take account of the variation of the absorption coefficient. 
The close connection between centre-limb contrast and variation of k v is 
shown by the occurrence of r„ sec 9 in (228-6); to double kjk is equivalent 
to transferring to a new point on the disc where sec 6 is doubled. When 
Fig. 5. Solar Energy Curve. 
— Observed intensity. 
Theoretical curve for constant absorption coefficient. 
Theoretical curve for constant emission coefficient.