TO KNOW THE STARRY HEAVENS 
7 
western part of the sky. They will soon 
be in unfavorable positions, leaving the 
evening sky without conspicuous plan- 
ets. On June 29 Mars passes the sun 
and becomes a morning star. It is too 
close to the sun to be seen now. Venus 
is brilliant as a morning star. Summer 
begins when the sun attains its great- 
est distance north of the equator, as it 
does June 21, 6:36 P. M. 
5|c jf: sfc ijc sf: 
The Pons-Winnecke Comet. 
The path of this interesting comet is 
shown in Figure 2. The ordinary comet 
approaches the sun in an approximate- 
Jupiter. Such a comet is called a peri- 
odic comet. There are about thirty such 
comets which are called Jupiter’s great 
family of comets. The outer planets 
also have small families of comets. This 
comet revolves about the sun in a pe- 
riod of about five and one-half years 
and, as the figure shows, once in each 
period comes close to the sun and the 
earth. We can see the comet only in 
that part of its path. From B to P the 
comet is above the plane of the earth’s 
orbit and elsewhere below. The angle 
between the two planes is nineteen 
degrees. 
ly parabolic path and leaves the sun 
to return, if at all, after an exceedingly 
long period of time. This comet in com- 
ing in toward the sun passed near the 
great planet Jupiter. Jupiter so changed 
its path that instead of leaving the sun 
it moved about the sun in the elliptical 
path shown. Jupiter’s influence is 
shown by the facts that the part of the 
comet’s path farthest from the sun lies 
near the orbit of Jupiter and that the 
comet crosses the planes of the earth’s 
and Jupiter’s orbits near the orbit of 
This comet was discovered by Pons, 
in France, June 12, 1819. On March 8, 
1858, Winnecke, at Bonn, Germany, dis- 
covered a comet which proved to be 
the same comet. Hence we call it the 
Pons-Winnecke comet. A comet was 
seen by Pons for three days in 1808. 
This may have been the same comet. 
The calculations necessary to prove the 
identity have not been made. A comet 
which was seen in 1766 also appears 
likely to have been another appearance 
of this same comet. Since 1859 the 
