Montgomery County sentinel. [volume] (Rockville, Md.) 1855-1974, 1874-11-27
miscellaneous.
How Eclipses Occur.

have said that the sun pursues GER
tain definite path among the stars, aboat
half degree wide, which you could see
if he left any trace there; 50. also, if you
could mark the position of the moon to-
night among the stars, and mark its po-
sition at every hour during her whole
course, you would find that she also has
pursned'a definite path among the stars,
but you would not find this path to be
the same as the suns path. If it were
the same, we should have an eclipse of
the sun every time the moon crossed the
sun, and an eclipse of the moon every
time that the moon passed on the other
side Of the earth from the sun But the
two paths are inclined to each other about
S degrees. They cross each other at
point which. in the month Of October.
1874, is very near the sun. The moons
path is south Of the suns in nearly all
that part of the heavens which we can
see in the evening Of that month but it
approaches the suns path, and crosses it
near the eastern horizon, and in most of
the invisible half of the sphere, or that
part below the horizon, the moons path
is farther north. All this will be clear
on examining the star maps, where the
dotted line shows the path of the moon
during 1874. crossing the suns path in
the consultations Aries and Libra.
These two opposing points in which
the moons path crosses the path Of the
sun are called the nodes. 1t is very
clear that unless the sun is near one of
the moons nodes when the moon herself
passes by, the moon will pass above or
below the sun, according as her path is
above or below that of the sun at this
point, and consequently there will be no
eclipse. Buff the sun happens to be
near the node, then the moon will neces-
sarily pass over his face and eclipse some
portion of him. Now, as have just ex
planned, there are two opposite nodes !;
TIE one set few hours ago, and the
other has just arisen. Since the sun
makes the whole circuit of the heavens in
the course of year, he crosses the moons
nodes twice in that time In 1874 he
crossed one node in May and will cross
the other node in November; consequent
ly it is only about these two times that
any eclipse can take place during this
year.
IF the moon always followed the same
path in the heavens, we could never have
any eclipse but at those two seasons -
But if we watch the motions Of the moon
for several years in succession, we shall
find that her path is continually chang
ing. 1t the present time she passes
seven degrees north Of Aldobaran a
month hence she will seem to pass the
star at almost exactly the same distance ;
bat if you continue your observation for
four or five months, you viii find that she
passes pcrceptibly farther north, and IN
three years you viii find that she crosses
it at the distance of about ten degrees. -
After that she would begin to cross further
south, passing near Aldebaran at every
revolution for eight years, until in 1888
and 1886 she will pass right over it. II
the moons path were painted on the
heavens. you would see that every time
the moon came round to the same point
in her path, which takes place about every
twenty-sevcn days, she would cross the
suns path about three Of her own diam
eteps sooner than the month before. In
the course of year, therefore, she will
have crossed about thirty-six diameters
sooner, or farther to the west. In thu
course Of twenty years you will find thai
this motion has been kept up until sht
crosses at the same point she does now
and thus the nodes have made q complete
circuit of the heavens The season o
eclipses vary, therefore. in the same man
ner. This year they are in May anc
October in five years from now they
will occur three months earlier. and w
shall have them in February and August
five years more, and they will be in Dc
tober aud May: five years more, in Au.
gust and February; FIVE years more, ant
they will correspond once more to what
they are now Hdrper's Mogasinc.