The Barre daily times. (Barre, Vt.) 1897-1959, 1907-12-30
Difference Between the Star
Day and The Sun Day
1T IS GREATEST IN WINTER
Why the Difference Occurs and How Il
May Be 0bseryed-0ddly Enough
Shortest Day in Year Il Really
Longest Day in Time.


qulred Tor the earth to turn once on
~ axis, that Il measures twenty.fonr
hours by the clock aud that a fraction
more than ae5 o. them arr 10 be found
ia a year
Il Il good plan when one reads
anything IA a book 10 test II when ho
can for himself. We want 70 see just
how long It takes the earth to turn
over once. let ns take any one Of
the Fixed stars that chances TO be IN
line with some convenient point and.
watch IN hand. notice the precise mo.
ment at which the star touches. lct us
say. a particular tree. branch or stee-
pie on the horizon line. n GA tho next
evening we stand at precisely the same
spot and sight The same star again IN
line with the same point as before,
then we shall know that the earth has
turned on lis axis Just once.
Curiously enough. however. we shall
discover. II this Is done carefully. that.
IA spite OF what the books say. Il does
not require fwenty-four hours for the
earth 20 turn over once. About four
minutes before the day Is up. BY the
clock. the earth has revolvod once and
brought the star back 10 its old posi-.
ton in the sky. Really, then. the earth
turns on is axis once In twenty.three
hours, fifty-slx minutes and four Sec
onds and, as ono can easily reckon,
makes something more than 800 revo-
iuiious N a year
But human beings are not so much
Interested IN the stars as IN the sun.
We really don't care much how long Il
takes the earth 10 turn over and bring
sar back again 70 the same point in
the sky or how many times IN a year
a star seems 10 go by. We set our
clocks and reckon our year by the
turning OF tho earth under the sun.
aud because the earth not only turns
under the sun. but also goes round Il.
II tnkes about four minutes longer 20
bring the sun up 20 its old place In
the sky Than 70 bring back n star. This
comes about simply enough. suppose
one Is In a room looking out the win
dow Mt tree. N he turns round once
exactly lie WIN fnd himself looking
straight at the tree again. but II be
tried the same thing when he was on
moving train he would flnd that
while he was making the turn the tree
had fallen behind. lie would then. ac-
cordlng to the way be twirled, have to
turn little more or a little less 70
bring the tree straight before his nose.
Therefore It Is not quite true that a
day IS the time required FOR the earth
TO turn once on It's axis. II really IL
this time Plus the four minutes or so
required for It 10 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 It's position.
Since the earth is some 100000 miles
nearer the sun IN winter than in sum
mer, and since also the nearer the sun
It is the faster 1t travels, the difference |
between star day and sun day is
greatest in winter
oddly enough. 1t 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 It does,
as matter OF fact, run almost half 4
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, il always the
same length. twenty three hours, fifty
SIX minutes, -four and e-hundredths
and there are 1906 Of them In
I year. Then there Is the ordinary le-
yai day, which is the time required for
/ proper clock to get round twice.
rhis Is Just twenty-four hours Be
,ides these, there is the sun day, its
line told by the .sundlal, which, TAX
NC short with long, averages twenty
'our hours, but Is never found to DO
exactly the same length for two days
n succession,
There is a string OF long days in the
winter followed By a series or short
mes Ia the spring. In the summer the
Jun days get long again, though not
luite SO long as in the winter. In the
autumn come the shortest days Of an.
)nly occasionally are clock day and
Jun day of the same length. Only
our times year do clock noon by
he clock hands and sun noon by the
undial occur at the same moment,
While. because the long and short sun
lays are found in sets, they oftentimes
nay be more than fifteen minutes
part
The vast majority of the people
eclon their time by the sun. But !
ime for civilized men is time by the {
lock. The days are all twenty-four {
ours long. and no matter where the |
un IS it is noon for MS when the clock
trlkes IL Nevertheless, astronomers
ften go By star time, get in an extra
ay Ia each year and have their noon /,
all at all times of the day or night
J. r, Brewster in Chicago Record-Her- /
ID. 4