South Bend news-times. (South Bend, Ind.) 1913-1938, 1918-03-04
The MarDeLs of
Haloes, Rainbows
and Mock Suns
BY Garrett y. Serviss.

one Sunday night, recently, about
II O'Clock. / remarked how beauti-
full and clear the moon was. A few
minutes later, going TO the window
again, was surprised to see a white
ring around the moon, such as we
see before a storm, and outside OF
that ring a perfect circle of a rain
bow. the coiors appearing very dis
tinctly. Is this unusual, and what
is it's significance Mrs. }. J. NJ.
What you saw was a very beaul-
full lunar halo. a phenomenon rarely
exhibited with so much perfection.
Although the colors were those OF
the rainbow, yet it vas not a rain
bow, and did the sky opposite TO the
moon i. e., rainbows are produced.
L you had taken notice of the ar
arrangement of the pr smatic colors
in the circle you would have seen
that the red was inside, whereas
in the rainbow the red is outside.
True lunar rainbows do occasionally
appear, but, like rainbows formed
by the sun they are only visible IN
the part of the sky opposite to the
moon. l. G., the spectators back
must be toward the moon Cor the
sum- Their colors are the same as
those of solar rainbows because
moonlight is nothing but reflected
sunlight, but they are comparative
" faint, because the intensity of
moonlight is so much less than that
of direct sunlight.
A rainbow never shows COM
pIete circle. but at the most only
a semi-circle, unless the observer
happens TO be at a great elevation,
as in a balloon, when more than
half q circle can be seen, but never
an entire one. Halos and rainooWs
also differ in the size of the circles
or semi-circles. that they exhibit
The radius of a halo is about p
degrees. and that of a rainbow
about AZ degrees. other arches and
circles are sometimes seen OUTSIDE
of both the rainbow and the halo,
but the radii given are for the prln-
cipaI. or primary. phenomena.
Another fundamental difference
between a rainbow and a halo Is
that the cause of the former IS
combination of the effects of retrac-
ton and reflection of light in a mass
of falling rain drops. situated in the
opposite part of the sky from the
sun or the moon. while a halo is
caused simply by refraction OF llsht
passing through a mass of floating
ice CRYSTALS in the same quarter of
the sky where the sun or the moon
is. In order TO have a halo II IS
only necessary that the light should
be turned out of its course (re-
fracted) at a certain angular dis
lance (about 22 degrees, or 40 de-
grees for a secondary halo) from
the luminous body by prisnatic
particles of ice in the upper air,
which. while turning the light from
its original direction and thus bring
ing il to the observers eye. at the
same time disperse the primary
eolors into a colored band.
But. TO have a rainbow. the light
must first enter drops of liquid wa
ter falling in a shower and be there
refracted. and have its primary col
ors dispersed by the water, and
then be reflected from the inner
surface of the drops on the side
opposite TO the sun. and thus be
sent back TO the observers eye,
which is situated between the fall
ing drops and the sun. In the re-
aection from the back of the drops
the order OF the colOrs is reversed
and the red comes out below, and
this causes the upper or outer Dor
Ter of the rainbow to appear red,
because if the red ray from par
ticular drop enters the eye the other
coIored rays viii pass above the
line of vision. but a violet ray from
a lower drop will enter the eye al
the same time as the red ray from
the upper drop. and thus the bow
appears red above and violet below
There is no similar reversal In the
colors formed by the passage OF the
light through atmospheric ice crys-
tails without reflection, and so in the
halo the red is on the inner and the
violet on the outer edge or the cir
Gle. Connected with the halos are
the amazing appearances called
mock suns" which sometimes al
most equal the real sun in bright
ness.
There are many other masnificent
phenomena associated with the
play OF sunlight and moonlight
among the floating vapOrs and crys-
tails OF the atmosphere. such as the
coronas. or "glories," that often ap-
near around the sun or the moon
when the air is filled with transEu-
cent clouds or with extremely min
ute particles OF water vapOr. Ike
tfn halo the CORONA Il formed In fhf