The Washington times., 1917-01-15
SUNSET MATTER OF
INTRICATE FIGURES
Even Official Calculation of
Time Show Eight Minutes
Variation.
BOTH TABLES ARE CORRECT
Difference Depends Upon the
Use of Standard or
Local Time.

What time does the sun rise in
Washington. What time does it set7
When it's up, and when it's down,
might suggest itself to the facetious,
but the automobilist who must have
his lamps lighted by half an hour
after sunset, does not appreciate any
hippancy on the subject.
Consequently he generally watches
the weather tables in the newspapers
for this information, CLEANED from
official sources. But, there's the rub.
He may see in one OF the morning
papers that the sun sets at one timeC
while in The Times he viii probably
see that It sets just eight minutes
later, giving him eight minutes OF
grace. How in Sam Hill, he asks, can
official tables on the subject disagreed
Is some one careless printing them?
And not finding q ready answer to
his first inquiry, he IL inclined to be-
lieve that the latter Is the case.
Discrepaaey Explained.
But such, gentle reader, is far from
the fact. Official tables OF the Coast
and Geodetic Survey say that the sun
will rise in Washington in q given
day, at a given hour. For the same
day official computations from. the
Naval Observatory will have the sun
rising probably eight minutes later,
and setting eight minutes later.
Both are correct officially.
Ia,.f 4hara aa fhfa HffYarance ThA Ma
val Observatory computation is based
upon standard time The Coast and
Geodetic Survey table. unless 1t hap
pens to be an especially prepared one,
Is based on local time.
Contrary to general belief. standard
time and local time are not the same
in Washington, though q lot of Official
scientific records and time computa-
tions are based on the meridian OF
Washington.
Consequently, IL you read the Coast
and Geodetic table of sunrise and SUM-
set, 1t will not be correct, according to
your watch, or the family clock. as
nearly all Of them are set by standard
time in Washington, which runs eight |
minutes ahead Of the sun
Philadelphia Not Slow. |
Philadelphia. being eight minutes in
longitude east OF Washington. is the
only city using eastern time that does
not have to make an allowance In
records Of this sort between standard |
and local time, as they are the same. |
1t il noon, standard time. in Philadel-
phia, when the sun is directly on the
meridian Of that city.
Why, you may ask, are the tables
not put in standard time, the time that
everybody uses, 30 there would be- no
possible confusion. Prof. W. s., Eichel-
berger, director Of the department OF
the nautical almanac Of the Naval OBJ
servatory, and DR.. z. Lester Jones, su-
periitendent Of the Coast and Geodetic
Survey, answer that 1t Is impossible.
In other words, 1t can't be done. |
simple as Il may seem to you, and as |
simple as It seemed to the poor re-
porter. He asked why 1t was not posi-
BILE 10 take all Of the cities In the longi-
tude Of eastern time. figure the sun |
rise for them by their longitude. and |
then put 1t all down in standard time.
And III bet you never the ught Of the |
answer either?
It was patiently explained that the
sun does not rise at the same hour In
two cities that may be on exactly the
same degree, or line OF Longitude.
Latitude makes q difference. Don't
you remember reading, in your old
geography, II not later, how long
the days are in northern countries In
spring and summer? And how short
they were In winter? The declina-
tion of the sun makes the difference,
II you know what that means.
varies with Latitude.
For instance with the sun north Of
the equator, the sun rises earlier at
any point on the longitude of Wash
ington, in far-off Canada, than 1t does
in the Capital, and sets later. In the
fall and winter, with the sun south
of the equator 1t is just the reverse.
Therefore, the time OF sunset and
sun rise, depends upon latitude, as
well as longitude, or the two COM
bined, and 1t is necessary to figure
the latitude and longitude of every
place to get the time straight. AS
time depends on longitude, of course
the figures secured, are always local
time figures, and 1t is not possible TO
print volume large enough to carry
a separate table for every commun-
ity, and they cannot be grouped by
standard time.
In other words-if you don't get It
that way-after figuring the exact
time by longitude that the sun will
rise at the equator, the center line
dividing the earth into north and
south hemispheres, it is necessary to
add to or subtract from this figure
as you move north and south, the
ratio Of the declination of the sun, or
its position north or south of the
right angle plane of the earth. But