20 ASTRONOMY • APRIL 2019W
hile my wife,
Deborah, and I
were traveling
in Nepal, our
housekeeper,
Shirley Shebadieta, was at our
house in Maun, Botswana, cap-
turing an unusual optical phe-
nomenon with her smartphone
on October 24, 2018. Shirley
was outside hanging clothes
when she noticed clouds
approaching and then covering
the Sun, producing a stunning
array of odd-radius halo arcs
(pictured at right).
Shirley said she was
impressed with the intensity of
the darkness within the circle,
saying that at times it looked
like an approaching storm.
Shirley’s best images show a
series of three equally spaced
(or near-equally spaced) halo
arcs well above the Sun and
two arcs well below, with
another 9°-wide halo centered
on the Sun.Shirley sent me the images,
and when I returned home I
borrowed her phone and took
images of the Sun in a blue sky,
to rule out camera defects and
internal ref lections as possible
causes for the radius halos. But
the abundance of images that
Shirley took at different angles
supported the reality of the
sighting. Having never seen
anything like this, I sent the
images to Les Cowley, who
runs the website Atmospheric
Optics, and asked for his help
to explain the phenomenon.
Les said the display was real
but “very strange.” Indeed,
after playing with ray-tracing
simulations using HaloSim, he
found the initial results prob-
lematic — until he set the Sun’s
altitude to 80° and let the
machine run out “millions of
rays through the [ice] crystals.”
And, voila! “On the screen,
Shirley’s display popped
straight out,” he said. The
results showed the 9° halo, plus
20°, 22°, and 24° halo arcs
above the Sun, and 22° and 24°
halo arcs below the Sun.
The next morning, I awoke
to an email from Les saying,
“There is an explanation of the
unusual sighting — but I need
the altitude 80° or more.” Once
again, Shirley lent me her
phone. The most unusual dis-
plays began at 11:41 a.m. local
time, when the Sun’s altitude
was 79°15'. Les was ecstatic.
Ordinarily, Les explained,
odd-radius halo displays are
created by randomly oriented
pyramidal crystals, but they
do not explain these halos.SECRETSKY
A rare solar
halo display
Strange sighting is caught on a smartphone camera.
“However,” he said, “put the
Sun very high and pyramidal
crystals oriented with their
long axes roughly horizontal,”
and we can reproduce Shirley’s
images. A full analysis can be
seen at http://www.atoptics.co.uk/
opod.htm.
Given that Shirley is not a
trained observer, she deserves
praise for making a drawing
based on her naked-eye view,
as well as taking some 40
images of the phenomenon
from different angles. “When
something unusual is detected
in the sky, always take several
images,” Les advises.
By the way, the odd-radius
halos have names after the
observers who first reported
them: The 9° halo is known as
Van Buijsen’s halo; the 20° one
is Burney’s; and the 24° halo is
Dutheil’s. While these halos
are among the most common
of the odd-radius halos, they
are rarely seen by one person.
Meteorologist Alister Ling,now retired from Environment
Canada in Edmonton, Alberta,
saw his first odd-radius halo
display (including the 9° halo)
in the spring of 2018, noting it
“only took 40 years of sky-
watching” to spy one.
As always, send your
thoughts and observations to
[email protected].BY STEPHEN JAMES O’MEARABROWSE THE “SECRET SKY” ARCHIVE AT http://www.Astronomy.com/OMeara.On October 24, 2018, this display of solar halo arcs was seen above Maun, Botswana.
It featured multiple arcs seen when the Sun was nearly 80 ̊ high. SHIRLEY SHEBADIETALes Cowley, who runs Atmospheric
Optics, sent this ray tracing for a 79°
high Sun and pyramidal crystals with
wobbly horizontal column orientations.
It neatly reproduces Shirley’s display:
three almost-equally spaced arcs
toward the zenith and two at bottom.
The 9° halo arc is very bright, just like
Shirley’s images. LES COWLEYShirley Shebadieta with her
smartphone. STEPHEN JAMES O’MEARAStephen James O’Meara
is a globe-trotting observer
who is always looking for the
next great celestial event.