Evening star., 1924-11-30
THE STARRY SKIES IN DECEMBER

At A, Fig. /, Is the star Omicron
LCeti. commonly called Mira, which
means wonderful. The wonderful
thing about the star is the fact that
1t changes greatly in its brightness
Mira was the first star in which vari-
ations of brightness were detected
Fabricius detected the variation In
1896. Mira is visible to the naked
eye for a few weeks at time only.
1t rises to a maximum of brightness
quickly. then fades out less rapidly
and disappears from naked eye vision
to appear again and reach its maxi
mum after about IL months. Its
brightness at the maximum is not
always the same. Sometimes 1t rises
to tho second magnitude and at
others only to the fifth. Since the
invention of the telescope we have
been able to see the star at all times
and we find that 1t descends to the
eighth or ninth magnitude. The in
terval between the maxima of bright
ness varies from $50 to $40 days and
averages 332 days almost exactly IL
months. The next maximum is ex-
pected about February l.
The constellation Cetus is not a
a triangle of stars and a quadri-
lateral OF stars. The general position
of the constellation Is eastward and
southwark from Mars At the first
of the month probably no trace of
Mira will be seen with the naked
eye. BY the end Of the month 1t
should be in sight
This star, which seemed to play
hide and seek with observers. was,
S,-I
star. The more than 325 years in
which it has been watched have not
lessened the mystery of It's be-
havior. Several thousand other stars
have been found to vary in bright
ness. About 500 Of them are vari
ables of the Mira type. That is, they
are stars with large and more or less
regular variations in light taking
place In periods from few months
to about two years. The cause OF the
variation in the light for these stars
the other four classes into which
variable stars are divided.
Astronomical Time.
Astronomers in historic time have
almost invariably counted their time
in days beginning at noon with the
hours numbered from 0 to "a. Civil
ians begin their days at midnight and
divide the day into two parts-a.rn
and pm. December 1, astronomical
time, does not begin until noon of
December l, civil time. 1t Is some
what more logical to count the days
as beginning at the time when the
sun crosses the meridian in the south,
an event which can be observed.
rather than to begin them at a time
when the sun cannot be seen at all.
1t is noon which is recorded by a
sundial-not midnight. Astronomers
observations are taken for the most
part at night and a change Of date
at midnight would cause some un-
certainty and inconvenience. Navi-
gators have also found 1t convenient
to begin their day with noon, for 1t
is that time that they observe the
sun to determine their latitude. AL
though the astronomer and the navi-
gator begin their days at noon, the
navigator uses a date one day in ad-
vance of the astronomer. Civilians,
however, who far exceed astronomers
in numbers, would find change of
date at noon very inconvenient. AL
though there are conveniences for
some in the use Of each OF the sys-
tens, there arc disadvantages in
having more than one system IN use.
In 1884 an international conference
was held at Washington for the pur-
pose of fixing a prime meridian and
universal day. Twenty-si nations
were represented Greenwich was
adopted as the prime meridian. The
following resolution was adopted
without division: THAT the confer
ence expresses the hope that as soon
nautical days will be arranged
IN hA1fp
night" However, those who directed
the preparation OF the aImanacs op-
posed the change, and no change was
made by astronomers. but navigators
have gradually changed to the use Of
civil time.
During the war period there was
renewed agitation for the abandon
ment Of the astronomical days, the
agitation starting in England. a
committee of the American Astrono-
mical Society investigated and found
that those nterested-astronome
navigators, etc.-favored the change
about three to one. Such changes
cannot be made Immediately, as the
almanacs are prepared several years
in advance, and, also, because there
must be due notice 50 that people will
be prepared for the change. Such
changes are also made in a year easy
~ lCiicIhbSAp DIS 1SVU, 1oGO, 1SOp. ne
present change takes place January
1. 1925. The change has been made
in The American Ephemeris and
Nautical Almanac" prepared by the
United States Government, which is
the source Of all American almanacs,
and in the similar publications of the
other countries of the world. Hence
forth there will be no astronomical
day and all statements referring to 1t
found In books upon astronomy will
have an application only to dates be-
fore 1925. The hours will continue
to be counted from o to "a, however.
That is, 2 pm. Will be called IA hours
This practice should be generally
adopted.
There will be some confusion. pos
sibly for astronomers and others u.s.
ing astronomical books, for time,
but the layman will not be affected
by the change. Layman have fire.
Quently made mistakes in the past by
misinterpreting the almanac. For in
stance, to find the time when Winter
commences, consulting the publica-
tion that is cited above, the original
source. / find that 1t begins December
2l, IA hours and 46 minutes, and the
Of ;e