1921.] 
Astronomical Notes. 
7 
The energy radiated from a nova during the first exceedingly brief stage, 
before it has had time to expand appreciably or to become surrounded by 
an extensive atmosphere, is carried chiefly by waves only a few angstroms 
in length—that is, practically the same as X rays. 
At 6,000,000° the waves carrying maximum energy have a length of 
under 5 angstroms, or about of that of the shortest known waves in the 
ultra-violet. X rays have wave-lengths of from to 10 angstroms. 
It is possible, though very unlikely, that an observing-station at a very 
high altitude might detect the outburst of a nova by electrical means before 
its visible light became noticeable. 
2. Next, according to Stefan’s law, the total energy of all wave-lengths 
radiated into space is given by the formula 
E H k0\ 
where k = 5-3 X 10 -5 in ergs per square centimetre per second. 
At a temperature of 6,000° absolute E — 6-869 X 10 10 ergs per square 
centimetre per second = 1,645 calories per square centimetre per second. 
According to Abbot, the solar constant (that is, the energy received per 
square centimetre per minute at the distance of the Earth) is 1‘95. This 
implies that about 89,700 calories are radiated from each square centimetre 
of the Sun’s surface per minute, or 1,495 per second. This corresponds, 
according to Stefan’s law, to an effective temperature of 5,806° absolute 
for the Sun’s surface. 
Assuming that the Sun gives out 1,500 calories per square centimetre 
per second from its surface, the average amount of energy which each gramme 
of its mass parts with per second is 
1500 X 6-0987 x 10 !2 
— 4-6443 X 10~ 8 calories. 
1*96975 X lO" 8 
