A preview of this full-text is provided by Optica Publishing Group.
Content available from Applied Optics
This content is subject to copyright. Terms and conditions apply.
Comments on Sun's Image on
Airborne Ice Crystals
Frank E. Barmore
Physics Department, University of Wisconsin, Madison, Wis-
consin 53706. Received 8 April 1968.
Recently, Deirmendjian1 reported observing the sun's image
in the air below the horizon from a jet airliner. The depression
of the image was equal to that of the sun's altitude. The size was
not given but from the description it might be taken to be on the
order of 1?0
Just such a phenomenom (die Untersonne) is discussed by
Pernter and Exner.2 Descriptions of several observations are
given (pp. 289 ff), two photographs of the phenomena reproduced
(pp.
291, 390), and an explanation given (pp. 400 ff).
All of the information in Deirmendjian's report indicates that
ice crystals in the form of thin hexagonal right regular prisms
with their axes vertical are the cause of the observed phenomena.
There could be a sufficient number of these crystals between the
observer and the ground without obscuring the view of the
ground as reported, particularly when one considers the usual
conditions of the windows in jet airliners.
Deirmendjian also mentions a paper by Barabaschov,3 which I
have not seen, that reported a quasi-specular brightness maxi-
mum seen on the disk of Venus. I suppose the implication is
that this may be caused by ice crystals in or above the cloud
layer of Venus. In connection with this, one might find interest-
ing the report by O'Leary4 of a marginal observation of the 22°
halo phenomena on Venus as the planet passed through the ap-
propriate place (cythereocentric sun-earth angle of 158°).
References
1.
D. Deirmendjian, Appl. Opt. 7, 556 (1968).
2.
J. M. Pernter and F. M. Exner, Meteorologische Optik (W.
Braumüller, Wein, 1922), 2nd Aulfuge.
3.
N. P. Barabashov, Vestnik Kharkov Univ., No. 4, Astron.
Series, No. 1, pp. 13-21 (1965).
4.
B. T. O'Leary, Astrophys. J. 146, 754 (1966).
1654 APPLIED OPTICS / Vol. 7, No. 8 / August 1968