The optical phenomenon of "Brocken spectre"
Item
-
Title (Dublin Core)
-
The optical phenomenon of "Brocken spectre"
-
Article Title and/or Image Caption (Dublin Core)
-
Specters That Haunt the Clouds
-
extracted text (Extract Text)
-
THE accompanying picture rep-
resents an optical phenomenon
that has been familiar from time
immemorial to the birds of the air,
but that has, until recent times, lain
somewhat beyond the purview of
humanity. Even at the present day,
though it is well known to aeronauts,
few of them are able to explain it or
to give it a name. The picture shows
the shadow of an airplane cast upon
the clouds, and surrounding it is a ring
of rainbow-colored light. The appear-
ance of this light has been likened to
that of the emblem painted on the
wings of the Allied aircraft, and super-
stitious aviators regard it as an omen
favorable to their cause.
Like the “Ring Around the Moon”
This phenomenon bears, however, a
German name, for it is known as the
“specter of the Brocken.” True, the
traditional Brockengespenst, which fig-
ures in German legend and in the nar-
ratives of mountaineers, is the shadow
of the observer seen on a vertical bank |
of cloud or fog, and hence visible only
when the sun is low; but it is identical
in character with the shadows that |
balloonists and aviators see below them
on a horizontal sheet of cloud, with the
sun overhead.
In both of these cases the sha-
dow may be surrounded with one or
more rings of prismatic color,— the
“Brocken-bow,” — though this is not
always visible. This bow is due to
light that is reflected back to the ob-
server after penetrating the cloud a
little way, and is broken up into its
component colors by the water drops
orice particles. The process involved is
called diffraction, and itis the same that
produces the reddish corona, or circle
of light, seen around the sun or moon |
when passing through fleecy clouds.
The weird shadows of themselves
seen by mountaineers are often de-
scribed as of gigantic size; but this is
an illusion caused by the impression
that the shadow is distant, when it is
really only a few yards away. It would
be interesting to know whether aviators
cherish the same illusion concerning
the shadows of their aircraft.
Our Picture Is Faulty
Another mistake about Brocken
specters is perpetuated by the various
drawings that have been made of them,
including the one here reproduced.
‘The mountaineer can see his own sha-
dow, but he cannot see that cast by
another person at a distance of more
than a few feet from him. Similarly,
the artist who made the picture above
has drawn the shadow and ring as
they appeared to the occupant of the
airplane shown in the picture; but,
from the assumed angle of vision of
the artist himself, the phenomenon
would have been invisible.
-
Language (Dublin Core)
-
eng
-
Date Issued (Dublin Core)
-
1919-02
-
pages (Bibliographic Ontology)
-
24
-
Rights (Dublin Core)
-
Public domain (Google digitized)
-
Archived by (Dublin Core)
-
Davide Donà
-
Marco Bortolami (editor)
Popular Science Monthly, v. 94, n. 2, 1919
Screenshot (493).png