6 
The N.Z. Journal of Science and Technology. 
[Mar. 
ASTRONOMICAL NOTES. 
The Initial Radiation from a Nova. 
By A. C. Gifford. 
The third body resulting from a collision between two stars is initially 
at a temperature of several million degrees centigrade. It is important to 
inquire into the character of the radiation emitted by such a body during 
its first few hours, as this stage in the life-history of a nova has not yet 
been observed. 
Let us assume that the accepted laws of radiation still hold at the 
exceedingly high temperatures involved, and see what conclusions follow. 
1. First, the wave-length of the rays which carry the maximum energy 
will be extremely short—that is, the bulk of the radiation will be far up in 
the ultra-violet, and therefore quite invisible. According to Wien’s displace¬ 
ment law, 
0X m = a constant, 
where 0 is the absolute temperature and A m the length of the waves carrying 
the maximum energy. If the wave-length is measured in centimetres the 
constant is approximately *29 ; if measured in angstroms it is 29,000,000. 
This leads to the following wave-lengths for the rays of maximum energy 
for different temperatures :— 
Red just visible .. 
773° 
absolute 
37,516 A. 
Dull red 
973° 
99 
29,804 A. 
Orange 
1,373° 
9 9 
21,041 A. 
White 
1,573° 
99 
18,436 A. 
Dazzling white .. 
1,773° 
9 9 
16,356 ,A. 
The Sun 
6,000° 
9 9 
4,833 A. 
10,000° 
9 9 
2,900 A. 
100,000° 
9 9 
290 A. 
1,000,000° 
9 9 
29 A. 
6,000,000° 
9 9 
5 A. 
10,000,000° 
9 9 
3 A. 
30,000,000° 
99 
1 A. 
These results are plotted in fig. 1. The wave-lengths of visible light range 
from about 4,000 angstroms in the violet to beyond 7,000 angstroms in the 
red. 
The table and diagram show that, even when a body is heated to so high 
a temperature that its light appears dazzlingly white, the waves carrying 
the maximum energy are far down in the infra-red. 
In sunlight alone of all ordinary light sources due to heat the maximum 
is within the visible spectrum. 
For all temperatures higher than 7,500° the maximum is in the ultra¬ 
violet. 
The shortest ordinary waves studied photographically have a wave¬ 
length of about 1,000 angstroms. 
If the maximum energy were emitted at this wave-length the tempera¬ 
ture of the body would be about 29,000° C. 
