Evening star., 1935-12-29
Keeping Time Straight


dimensional dynamic complex Of sun,
their recurrent spatial relationships.
To adapt this for practical purposes,
it Is essential slightly to idealizs them
and to endow them with q mathe-
NAUTICAL regularity which they do not
actually possess. This makes it nee
cessary from time to time to intro
duce corrections.
A YEAR Is like the revolution Of a
n wheel without any distinct
markings on its rim. It has been
necessary to provide some arbitrary
markings, for the sake Of keeping
the practical events of the world
straight in the matrix Of unalterable
time and Of correlating the tenn
poral with the eternal. Terrific Ia
bors through the centuries have gone
into the task. The year makers"
have not had mathematics and as
tronomy alone to consider. These
have been all tangled up with the
errors and customs of the past-with
tradition, history, religion, law, busi-
ness and art. In view Of all this the
actual year of the calendar consti-
tutes a remarkably delicate compro-
mise.
Why does the year start in the
middle Of Winter?
Perhaps the most valid reason, DR..
Robertson explains. Is that the first
day Of January is conveniently near an
annually recurring celestial landmark
the earth's perihelion, or point Of
closest approach to the sun. It's
fact that in the dead of the northern
Winter, due to our planets elliptical
orbit, we are few hundred miles
closer to the solar disk than on the
hottest day in Summer.
New Year day doesn't exactly hit the
mark. On or about January the
center of gravity of the earth-moon
system is nearest the center of gravity
of the sun. That is, two imaginary
points are closest together. One Is az
approximately the center Of the sun
and remains constant through the
ages. One is about 1000 miles below
the surface Of the earth, representing
the combined center Of gravity Of the
earth and the moon, and this is SUBJ
ject to considerable shifting.
Historically the Gregorian calendar
was established before there was any
exact calculation Of the earth's orbit.
The year was intended to represent the
time elapsed between Winter solstice
and Winter solstice-its beginning de-
termined by the point in time when
the sun apparently turned In its path
and began its six-month journey
northward. This, of course, actually
happens on or about December 81, but
by January l it was clearly observable
see the procession Of the days, each
trifle longer than the day before.
QUT the time of the Winter solstice
~ shifts more than the time Of the
perhelion and the latter is nearer to
New Year than the former. Hence it
Is a more convenient reference point.
So the year, as we know it. can best be
considered as the time Of one complete
revolution of the earth-moon around
the sun between perihelion and perl
helion. Neither solstice nor perihelion
would be, per Sc, convenient as an
| exact starting point because the times
Of their recurrence vary by hours from
year to year. The arbitrary time of
| midnight, January actually repre-
senting nothing in itseh--is good ap-
Proclamation between them. r.
The spin Of the cosmic wheel be-
tween perihelion and perihelion-the
nearest cycle related to the actual
year so far as dates are concerned-is
known as the anomalistic year. The
mathematicians at the Naval Almanac
ONCE calculate three other kinds of
year, differing from each other by
fractions of seconds. One is the
tropical year, the time which elapses
between vernal equinox and vernal
equinox. Still another is the sidereal
year-the time between the appear
ances Of the same star in the same
place at the same time from the same
position on the earth's surface-as at
| midnight over the meridian Of Wash
ington. But In computing this year
the astronomers use a hypothetical,
ideal star which Is an average Of all
the stars. In this kind of year any
day might be considered as New Year.
The fourth kind Of year isn't very
important, except in the theoretical
| calculations of astronomers. It is the
eclipse year - the time that would
e. .pse between eclipses of the sun and
the moon If both these bodies could
be considered as mathematical points
| with no external forces acting upon
them except their mutual gravitational
attractions. If this ideal situation
acually obtained eclipses would recur
to the split second, year after year.
There are at least four year, two Of
the sun and two Of the moon.
60 THE year 1886 will have four
lives, with each life differing a
little In length from all the others.
The differences are only matters Of q
few thousandths of a second, but piled
up over long periods they become Of
considerable importance. In case any
body is interested the year Of the cal
endar will be precisely, according to
Dr. Robertson's calculations, 365 .243,-
1876, ,6410 days. The year 1887 will be
614 ten-millionths of "a hours shorter.
This Is the tropical, or ordinary, year,
which runs between vernal equinox and
vernal equinox, although in dates the
year Of the calendar corresponds more
closely to the anomalistic year.
All the other kinds Of years are get
ting longer by correspondingly minute
amounts, more in accordance with the
actual astronomical state Of affairs
considered over unimaginable stretches
Of billions Of years. The eclipse year
is lengthening more than any Of the
others Just at present. Astronomers
calculate that in some far distant
future, as by imperceptible degrees the
gravitational attraction between earth
and sun decreases and the planets
orbit widens, the increase in the years