THE OCCULTATION OF VENUS BY THE MOON ON 
JANUARY 13, 1923 
P. BIEFELD 
An occultation of Venus, like a total eclipse of the Sun, is not 
in itself of infrequent occurrence, but for any one place on the 
earth’s surface it is extremely rare. The last one visible in this 
section of the United States happened early in December of 
1878. 
At Granville (Swasey Observatory) during the night hours 
preceding the event the sky was almost completely covered. 
At about 3:00 a.m., however, the sky cleared completely and 
Venus shone brilliantly some distance east of the Moon. 
Venus was about two weeks past maximum brightness but 
still about 130 times as bright as Aldebaran, the follower of the 
Pleiades. The Moon was three and one-half days before ^^new,” 
showing a slender crescent. 
It was a superb sight watching the slow but steady approach 
of the two objects. Apparently a collision seemed inevitable; 
but only apparently so. The catastrophy was sure to be avoided ; 
the Moon being only about a quarter million of miles from us, 
while Venus kept at a safe distance of about 47,000,000 miles. 
The Moon merely covered up Venus in the line of sight by pass- 
ing over her on the celestial sphere. 
Quite a number of last year’s and this year’s students of 
Astronomy being present, no attempt was made to observe 
accurately with the 9-inch the first and second contacts at im- 
mersion and emersion, nor were micrometric measures of these 
points with reference to the north point attempted. It seemed 
more practicable for the benefit of the students to demonstrate 
a photographic method for deriving approximately the time of 
emersion and duration of occultation from two photographic 
exposures before and after occultation respectively and from the 
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