The aegis & intelligencer. [volume] (Bel Air, Md.) 1864-1923, 1907-10-25

earth to turn over once. About four
| minutes before the day is up, by the
clock, the earth has revOlved once and
brought the star back to its old posi-
ton in the sky. Really, then, the earth
turns on its axis once in twenty-five
hours, fifty-siX minutes and four sec
onds and, as one can easily reckon,
makes something more than 1866 revo-
lutions in year.
But human beings are not SO much
interested in the stars as in the sun.
We really don't care much how long it
takes the earth to turn over and bring
star back again to the same point in
the sky or how many times in a year
star seems to go by. We set our
clocks and reckon our year by the
turning of the earth under the sun,
and because the earth not only turns
under the sun, but also goes round 1t.
it takes about four minutes longer to
bring the sun up to its old place in
the sky than to bring back a star. This
comes about simply enough. Suppose
one is in q room looking out the witt
dow at tree. If he turns round once
exactly he will find himself looking
straight at the tree again, but if he
tried the same thing when he was on
moving train he would find that
while he was making the turn the tree
had fallen behind. He would then, ac-
cording to the way he twirled, have to
turn u little more or a little less to
hrJp hn fra or tohf hofnrn
Therefore it is not quite true that a
day is the time required for the earth
to turn once on Its axis. 1t really is
this time plus the four minutes or SO
required for 1t to turn and look back
at the sun. The time required for this
extra turn is not the same at all times
in the year. One can easily see in the
case of the moving train that the fast
er the cars were moving or the nearer
the track the tree stood the more the
latter would seem to shift its position.
Since the earth is some 100000 miles
nearer the sun In winter than in sum
mer, and since also the nearer the sun
1t is the faster it travels, the difference
between star day and sun day is
greatest in winter.
Oddly enough, it happens that Dec.
%, which has the least daylight OF
any day In the year and Is therefore
commonly said to be the shortest Of
all days, is really the longest. 1t does,
as matter Of fact, run almost half
minute over twenty-four hours, while
the true shortest day, which comes on
Sept. II, falls short by about the same
time.
So we really have three different
days" There is the star day, which
is the time during which the earth
turns over once. This, because the
earth spins steadily, is always the
same length, twenty-three hours, fifty
six minutes, four and nine hundredths
seconds, and there are 366 of them in
year Then there is the ordinary le
gal day, which Is the time required for
a proper clock to get round twice.
This is just twenty-four hours. Be
sides these, there is the sun day, its
time told by the sundial, which, tax
ing short with long, averages twenty
four hours, but is never found to be
exactly the same length for two days
In succession.
There Is a string of long days in the
winter, followed by a series of short
ones in the spring. In the summer the
sun days get long again, though not
quite so long as in the winter. In the
autumn come the shortest days of all.
Only occasionally are clock day and
sun day Of the same length Only
four times year do clock noon by
the clock hands and sun noon by the
sundial occur at the same moment,
while because the long and short sun
days are found in sets, they oftentimes
may be more than fifteen minutes
apart.
The vast majority of the people
reckon their time by the sun. But
time for civilized men Is time by the
clock The days are all twenty-four
hours long, and no matter where the
sun Is it is noon for US when the clock
strikes u. Nevertheless, astronomers
often go by star time, get in an extra
day in each year and have their noon
fall at all times of the day or night
E. T. Brewster In Chicago Record-Her-
aid