The Washington herald., 1921-12-18
EARTH Is NEAR
sun AS WINTER
BEGINS, DEC. 2
Season Changes Depend
On Changing Tilt of
Earth's Axis.
Sunday. December is, 1921.
ny isabel VI. Isewis. OF the 4. q.
Naval Observatory.
LOO 900 MILES PROM
SUMNER TO WINTER

SUMNER TO WINTER.
When winter begins in N.
northern hemisphere on pecer,h,.
p. at eos a. m. Eastern ,,snd.rs
time. we will be 1000. 900 nJl.,
nearer TO the sun than we We.
at the beginning OF summer la,
June. The earth reaches nerfb,sI-
ion. the point in it's orbit nesrcs,
the sun. on January ,. II Vii,
then be about 1886. 900 miles iron,
the sun. II was in apheIio,, ~.
point IN it's orbit farthest rom
the sun. on July and is a.,
lance from the sun was then hon,
s4.S46.000 miles. The mean a.
erage distance OF the earth rro,,
the sun is about sc.Ss7 COO mile.
50 the least and greatest distsnc.
differ about 100000 miles from
the mean.
As our seasonal changes d.n.,,
F, far more upon the con,tantly
! changing angle at which the suns
( rays strike the surface. caused ~
I the tilt OF the esrth's axis 10 10
plane OF its orbit, than upon oou-
paratively small changes ia ~.
distance Of the earth from tho 81,
We feel no great effect from ms
/ change in distance.
Our winter begins when the 50,
reaches its greatest distance so,,tb
OF the equator. This time can 10
( computed 70 the minute and ID
never varies much over a dav fror,
year TO year At that time tho
( sun passes tnoon through Tie
zenith Or all points in p de-r,es
twenty-seven minutes South T.atf-
tude. and summer begins in the
/ southern hemisphere az the same
instant that winter begins IN gu.
/ northern hemisphere. Tho sru .F.u
starts it's northwsrd journey 90
crosses the equator once moe q
the beginning OF spring
Since the summer % the south
ern hemisphere occurs when rio
earth is nearest the sun and ...
winter when IL Is fsrthcst .-..u
the sun we would naturally
, pect TO find the Summers D.. rHe
southern hemisphere hotter rrso
our summers AMI the winters ...r,r-
er than our winters But tho cath
rs moving most rapidly when 90 Is
nearest the sun and most slowly
wheh IL Is fsrthest from tho sun
As result the summer o. the
southern hemisphere is about seven
days shorter than our summer and
while the heat Of the summer IS
somewhat more Intense IN the
southern hemisphere Il is received
for a shorter period. A. a result
there is very little difference IN
the total amount OF heat received
DURING the summer season in the
two hemispheres
The winters OF the southern
hemisphere are both longer and
colder than the winters o. the
northern hemisphere as they oc-
cur when the earth Is farthest
from the sun and IS. at the same
time moving most slowly in its
orbit In about 10000 years these
conditions will be reversed owIn9
to certain slow changes not takfnr
place in the form and position 81
the earth's orbit The winters IN
our hemisphere will then be Longer
and colder than the winter. OF the
southern hemisphere
Some biologists go SO FAR as 70
sa- that the glacial periods are
cause, ly this alienation In the
relative intensity OF winter IN the
two hemispheres. II is certainly
true that at present time the south
polar cap extends farther into the
temperate zon than the north polar
cap.