1921 .] 
Astronomical Notes. 
191 
ASTRONOMICAL NOTES. 
Ephemeris of a Comet. 
By C. E. Adams. 
Astronomers in the Southern Hemisphere are frequently at a disadvantage 
compared with their northern colleagues, as practically all comet predic¬ 
tions reach New Zealand too late to be of use. It becomes necessary, 
therefore, to undertake such calculations in New Zealand, and to this end 
the following notes have been prepared in sufficient detail to enable others 
to apply the method. 
The notation adopted is that given by Plummer* in his Dynamical 
Astronomy. The calculation of the comet’s ephemeris is made as simple 
as possible by adopting equidistant values of the eccentric anomaly. This 
method avoids the troublesome solution of Kepler’s equation. A slight 
disadvantage arises from the fact that the resulting positions of the comet 
are for irregular dates, but this is of no importance in an ephemeris 
which is only required for finding the comet. 
The example selected is the Pons Winnecke comet, of which the following 
elements were calculated by Professor Crawford and Miss Levy at the 
Students’ Observatory of the University of California from observations 
of the comet’s positions on April 12, 19, and 29:— 
Time of perihelion passage 
Perihelion minus node 
Longitude of node 
Inclination 
Perihelion distance . . 
Eccentricity 
Periodic time 
Elements.| 
.. T 
1921 June 12-95 Gr.M 
. . w 
170° 34'. 
.. & 
97° 51'. 
i 
18° 50'. 
• • C 1 
1 -040. 
e 
0-6779. 
.. P 
5-80 years (assumed). 
The comet describes an ellipse round the Sun with the Sun in one 
focus. 
From the elements the following particulars of the ellipse are derived :— 
Semi-major axis — a = - ^ - = 3-22881 ; 
semi-minor axis —b=aV 1 — e 2 = 2-37367 ; 
mean daily motion — n = - a - = 611-565" (k = 3548*1876"); 
ae = a — q = 2-18881 
lif = 5-20925 
1 — e 
\/M L - e = 2-28238 
1 — e 2 = 0-54045 
Vl - e 2 =0-73515. 
* H. C. Plummer, An Introductory Treatise on Dynamical Astronomy, Cambridge, 
at the University Press, 1918. 
t Harvard College Observatory Bulletin 751, Cambridge, Mass., U.S.A., 1921, May 4 
