The Houston daily post. [volume] (Houston, Tex.) 1886-1903, 1898-04-24
AuR0RA CYcLEs.
The Twcnty-Srvcn Dny Aurornl
Period and thr Moon.


The Twcnty-srvrn Dny Aurornl
Period and thr Moon.
tBy H. Helm Ciybton. Continued from last
week.
Each group OF auroras of fifty period,
shows the same general distribution OF a,l.
roras as the totals. In order to see whether
the period remains the same through tn,
different seasons of the year, two group
OF data were classified into periods, as de-
scrlbed before, and summed for the winter
and summer half year separately.
The data for the two groups were taken
from tables found arranged conveniently
for the purpose the first by Dr. yeeder iu
the proceedings of the Rochester Acadam,
OF Sciences, vol Ii, Plate 2, and the other
by the editor OF the United States Monthly
| Weather Review In that publication. The
| first covers the four years 1856 to 1883, and
| the other the three years from October
1893, 10 October 1895. These show that
there is a strong indication OF the reversal
of the period between the winter and sum
mer half years.
In the winter half year the maximum is
found near the time OF the greatest South
| ern declipation OF the moon while in the
| summer half year the maximum Is found
| near the time OF greatest northern declina-
| ton OF the moon. In attempting TO DIS
| cover the cause of this phenomena / no.
| ticcd that In my table OF auroras arranged
| in periods OF twenty seven days there was
strong drift of the larger numbers to tac
| right, and of such an amount as to indi-
| cate period OF about twenty nine days
| between them. This period | ut once In
| ferred to be the same length as the synod
| lie revolution OF tho moon, and Its cause 10
| lie In the fact that more auroras were seen
N I..#i 10 tt,.~
site phase.
| In order 10 determine to what extent the
frequency OF reports or auroras was thus
affected. the intervals from 1855 10 1888
and from 1894 10 1886 were divided into ne
RODS OF thirty days, beginning each period
with the date OF full moon as taken from
the Nautical Almanac
The number OF stations In the United
States reporting auroras on each date WIS
entered in table in its proper place be-
ginning With the date OF full moon, and
the totals were obtained for each day of
the period during the two intervals men
toned
The results show the very marked excess
In tho number OF auroras reported between
last quarter md new neon. This is the
Fart of the lunation when no moonlight &C.
ours between sunset and midnight tho part
of the day when rost records OF anroras
are made, because the observers are then
awake
but why there should be n greater num-
Der of auroras near the last quarter than
near now moon is not very evident, The
frequency OF auroras Is almost twice AZ
great near last quarter as near new neon.
and IN the mean OF .each consecutive five
the maximum number OF auroras occurs
exactly at tho time of last quarter.
This greN variation In the number OF
nrroras according to the age of the moon
furnishes u N fbn M ~ ~
time of maximum frequency of auroras IN
the twenty-seven day period. as n result
or which the maximum occurs near the
time of the moons greatest northern dc
clination In summer and near the time OF
the moons greatest southern declinatlon
In winter.
In the summer the greatest southern de-
clinatlon OF the moon occurs near full |
moon, so that the chief maximum of au-
roras occurring at chat time Ii ohscured |
In the winter the greatest northern de- |
clinntion occurs near full moon. so that the |
secondary maximum ut that time is OBJ |
scured, and the chief maximum at the Tina
OF greatest southern declinatlon is well |
marked.
But ms yet there appears no reason why |
there should be a secondary maximum or
auroras AZ the time OF the moons great
est northern declination, for according 10
Ekholm's theory OF the moons induction
IN notentia, het,yean ,he s ~ ,"s ainsl'nre
purht 10 no nj MN, vH' y, anu my alr
The moon's rrsat.st nnrtasrn aee,,, a,H,s ot
~ Is well known that when the sun
thcre Il ms p o W ay, ,r. enrsns EQUATOR
~ au,o1ns ms we,, shown for the
n nmssn 800 MS, ~ .ne iouowlns table. nrc-
hsr =, s,a,,nns r rano,,,. moving lhe num-
nsr OF s.ltons reporting auroras during
each or the Twelve mouths OF the year for
M ,n.efVai OF twenty-ihree years.
9sa '',.'...., .,,....,..s....,,...l 1908