Watertown republican. [volume] (Watertown, Wis.) 1860-1906, 1875-05-05
Astronomy 5.
COLLEGE OF THE SACRED HEART, !
WATERFOWL. MARCHl7 1875.

last article. Here is one of the difficulties
with which a new beginner has to contend
we say, The highest point the San can at
tain, this is only iguratively speaking, il
is the motion of the earth in its orbit tina
causes the deception, for deception it is
onr eyes show US the sun in motion from
east 10 west, we see the shadows of trees
and houses all moving from west to east,
Jet our understanding and learning teach
US that it is ourselves who are in motion
from a0est to east, although we do not feel
it, we see the heavens pass as we would
seq objects On land do, when we are in a
rail road car or on deck of a canal boat
When the sun crosses the line at each of
the equnoctial points, it does so at an angle
of 2330, this is called the o6liquy of the
ecIipHc. it is this obliquity that causes the
difference In the length OF the days and
nights and in the seasons of winter aud
summer. When the sun is in either of the
solstices the places in the same hemisphere
with it have their longest day and shortest
night and those at the other, their shortest
day and longes: night; when it is in either
of the equinoxes the days and nights are of
equal length in all parts of the earth ex-
cept at or very near the poles.
When the sun is in either of the equinox
es, one half of it would constantly appear
above the horizon Of a place at either of
the poles except for refractiou, the effect of
which would be very great, so that the sun
at the equinoxes appears wholly above the
horizon; thus causing constant day with
in one or two degrees of each pole, the
general effect of retraction is to increase
the length of the day from six to ten
minutes. When the sun is a short distance
below the horizon, its rays fall on the up
per portions of the atmosphere which like
mirror reflects them upon the earth, and
thus produce that faint light called taoiiiqht
In the evenings, and generally daaon in the
mornings. The duration of twilight varies
greatly al different parts of the earth 1t
is shortest at tie equator and increases
towards the poles near the polar circles
and within them there is constant twilight
during part OF the year. Twilight does
not cease until the sun is about l8o below
the horizon. In many parts Of Europe a.
IN the latitude of Dublin, twilight extends
far into the night, and on some days in June
the twilight and dawn almost meet so that
there is no real night.
Cnn thfo
mer or northern solstice) the north pole is
presented to the sun and we have summer
in the northern hemisphere, because the
rays of the sun fall directly on that part OF
the earth, while winter occurs in the south
ern hemisphere because there the suns
rays fall obiiquely. When the sun enters
Capricorn (the southern solstice) the south
pole is presented to the sun, aud summer
occurs in the southern hemisphere and
winter in the northern When the sun en-.
tiers either OF the equinoXes, as it does the
sign Artes or the vernal equinox on the
10th of March, the earth's axis leans side
ways to it, and the suns ray are directed
to the equator and equally obiique on 10th
sides Of 1t. Consequently their is neither
summer nor winter, but spring in that
hemisphere which the sun is entering and
autumn in that which it has left Summer
is caused by the rays the sun being more
perpendicular than in the other seasons. so
that the same part of the earth;s surface
receives greater quantity Of light and heat
Winter is caused by the greater obllqufty
OF the suns rays, IN consequence Of which
he same quantity OF light and heat is
dlHused over greater surface.
The seasons are not pIecisesy Of an equal
length, because the earth revoves in an
eclptical orbit, and consequently passes
through one half Of it in less time then
another The perfection of the eafth's or
bit, that Is, the nearest point Of it
to the sun, IS III the lltho Of Cancer, its
Longitude being 1000 IN SO that when the
earth is at this point the sun isin the lItho
OF Capricorn, January lst. Thus the earth
passes its peribeion and is cons equen Fly
nearest TO the sun in winter. And the
time occupied by the sun in going from
Libra to Aries that is from the beginning
OF autumn to the beginning OF spring is
shorter by about days, then the time from
Aries to Libra or from spring to autumn
again the seasons are of course reversed
in the southern hemisphere
The comparative length Of tie seasons
same length. About two thousand years
ago the aphelion must lave coinsided with
the verbal equinox and hence the seasons
Of summer and auslmn must have been
equat and also those Of spring and winter,
and the former must have been shorter
than the latter. About 10000 years ago.
the earth was nearest to the sun in summer
and farthest from it in winter, and the
length oft seasons the reverse Of what
they are now. This would make the sum-
mers OF the northern hemisphere according
to the calculations of sir John Herschel go
warmer then they are now. The earth is
about million of miles nearer the sun in
winter then it is in summer and this
causes it to be several degrees warmer in
the southern then in the northern sum-
mer. gfs
A million is so vast a number that we
can form no true conception of it without
dividing it into portions. To count
million at the rate of 5 per second Ia feat
almost lmpossible) would require about p
days counting day and night. A railroad
car running at the rate OF 80 miles per
hour night and day would require nearly
70 L