The Seattle post-intelligencer. [volume] (Seattle, Wash. Terr. [Wash.]) 1888-1914, 1891-12-21
sun, MOON AND STARS.
How Times Of Rising and Set
ting Are Determined.
EXPLANATION OF THE METHOD.
How Venus, Mars, Jupiter and Saturn
Will Light Morning and Even
ing Sky in 1892.

CHEHALIs, Dec. N.-lSpeciai Correspondence.
How 60 men find the times when the sun.
moon and stars will rise and set? This IS a
common question and il is the purpose OF this
article 20 answer il.
The problem is one Of the simplest in astron-
orny and BY employing sim pie methods believe
the principle on which its solution depends can
be made Gear TO all. Now for beginning let
US transport ourselves TO the ezrth's equator
and examine the appearance OF the heavens at
that place. The prominent features we mote
are:
FiTst-The great circle OF our horizon pas ses
through the poles OF the EeaIe ems, and the north
star lies very nearly q. tae north polat OF the
horizon Ut would appear exactly a. the nor;n
point were the star exactly st the north celestial
polel.
Second-The diurnal motions OF the heavenly
bodies are made in circles AZ right angles 70 the
horizon. II We extend the plane OF the earth 3
equator until u meets the eelestla. sphe-e q
great cree on the 3eaFens VII De iotTae4,
called the ''eelestial 90 lator. Inls circle d.
Yides the horizon into two equal parts a. the
east and west points, passes through oar zenith,
and IS parallel 20 every circle in which the
heavenly bodies make their daily revolutions.
THRIFT through ths zeuilh We pas another
great circle at right angles u tae cSiesIlai
equator, this new cireie VIII pass through the
pOss and soTIls celestial MERRIAM Tals
meridian circle viii divide our nor lZon into
two equal parts al the north and south points
We are now prepared TO examine the motions
OF the heavenly bodies es they rise and set each
day.
II we note the interval that elspses from the
rising 10 the setting OF a star, We will discover
that this interval is just twelve hours, and We
VIII also discover tGat al interval Of twelve
hours passes from the setting the rising. This
is true OF the sun, but not quite true OF the
moon, on account OF her rapid eastern motion
in the heavens.
IN xf sha he inf al f-1r
rising 10 setting and from setting TO rising is
over twelve hours, for the reason just given,
but the two intervals are very nearly the same.
SO We may lay down the general rule that, st
the equator, the heavenly bodies occupy the
same time from rising 10 setting that they &C.
eUpy from setting 20 rising. IN other words,
they are above ami below the horizon Tor equal
periods of time.
Now, why is this?
The great circle OF the horizon divides the
celestial sphere into two equa. parts, one half
OF the starry sphere being above the horizon
aud TIE other half below il. Our zenith is
always II the center OF the visible half. This
law OF the horizon governs in every latiiuce;
but q. the equator the zenith is, before stated.
in the celestial equator. Now, il is q we'll known
principle that all parts OF a revolving sphere
make revolution il the same time
This law applies TO the diarl2l motions OF
the heavens So Il matters not whether q star
be near tie pole al the equator or a. any inter
mediate point one revolution IS made in just
the same length o. time. Of course, the circles
OF revolution viii grow smaller we travel
from the equator 10 the pole. Bat these circles
viii ali DC ps =liel ~ the celestial equator, ana
If the circle Of the horizon cuts the celestial
equator at right angles II will also cut ali
parallel circles az right angles.
Ii It's weu-known theorcm that il upon a
sphere we draw two great ci-c,es they Will di-
! a
both the horizon and celestial equator are
great circles they bisect each other. The hori-
z0n 5isecting the celestial equator also biseets
every other circle parallel 20 il on the celestial
sphere. Hence Il s tast ths circles o. Tevolu-
ton OF sil the heavenly bodies are cut into two
eqnal PARTS by the horizon at the equs,or. and
therefore they revolye for an equal length IF
time above and below the horizon
Let Us pass 20 the meridian circle aud see
what part it plays in determining the motions
Of the heavens. he mcri1ien circle is we
have seen. great circle, meeting the horizon at
the poles. As the horizon divides the celestial
equator and lis parallel circles into Two 60 aal
parts, so the meridian divides these same circles
into two equal parts, a!ways cutting them at
right angles. The meridian is the halfway line
between the east and west arcs OF the horizon.
Therefore the interval that passes between the
rising and setting OF heavenly TO " Is equally
divided by The meridian: that is II star ap-
pears a. owe tbs horizon twelve hou-s il viii be
six hours in passing from the eastern Il !e o. the
horizon to the Iae!i3ian. ana SIX hours more in
passing from the meridian 70 tie western side
OF the horizon.
Lei Us apply these principles 10 the sun. He
is the monarch OF the heavens, the great dictator
in the kingdom Of time. for his place in the heav-
tells The time OF day. Il IS noon or y o'clock
when the sun i on the meridian. Ii he is two
hours east OF the meridian, il is Il O'Clock g. m ;
T M hon a-F sr-- ~ -
O'Clock ?. n, etc.
II we imagine great circle 70 pass through
the poles and center OF the sun. this circle will
accompany the sun in his diuraal revolution
Let Us call this circle the solar hour hand -
Tie place where The solar hour hand cuts the
J celestial equator determines the suns place in
the heavens, with reference - tae meridian, and
therefore determines the time o. cay.
/ At the time Of the eQuiaoxes March % and
September - tGe sUa's diuInai motion IS in the
celestial equator, and a. tGa, time his place in
the equator W.. give the time. But any other
time OF the year the sun Is either nosth or south
! o. the equator, and then tie place Of the solar
hour hand must De noted il order TO determine
the time. But whether in the equator or north
or south o.! il, the Will always remain twelve
hours so0ve the horizon aud twasve hours
below the horizon; aud since i; IS Il O'Clock
when the sun Is on the merldIan. he Will rise at
+ o clock a m and SET az o'clock p. n, eppar-
+ ent time, during the entire year.
( 50 the problem OF finding the time OF sunrise
! an3 sunset al the equator is yery simple one.
TO And The time Of rising or setting OF star
/ We have only 10 ma the time when the star is
( on tie meridian. which may Be easily found by
4 the Nautical Almanac II from This time we
sObtr2c; SIX hours we have the time OF rising:
i We add six hours we have the tine o. setting
Now le; Us see what phase the problem as
sUules when We lake our station north OF the
I equator. IL order 70 Understand this We must
Keep n mind the great circles that assisted Ia
/ al the equator. WHAT are they9
/ First-The circle III the equatorial horizon.
+ where TIE sun always appears a. O clock, su-
! parent time. N the morning and evening
+ eScoal-IAe ee -es+ial equator, which meets
the hoFtZ9n a. right angles, and divides X into
Two equal parts at the east and west points
| 41lTd-lGe meridian watch passes the celss-
tis- equator 81 riGht angles in our zenith, and
/ meets lAe horizon "a! the poles OF the heavens.
/ asa3A dividing the horiEon into two equal paris
/ a. TIE north aud south points
/ NS r. Sar ~ I ~ 49,