Astronomy

64 ASTRONOMY • JULY 2018

n uncommon solar

halo display for

subtropical lati-

tudes occurred

over Maun,

Botswana, last February. It’s

called a circumscribed halo,

and the sight of it brought to

mind another type of halo that

may adorn some hieroglyphs

in ancient Egypt.

Searching for solar halo

phenomena requires not only

some knowledge of clouds (and

sunglasses to cut down on

glare) but also a habit of look-

ing up more than down as the

day progresses, as some phe-

nomena can be f leeting. Here

in Botswana, occurrences of

the 22° solar halo and its asso-

ciated ice-crystal phenomena

— induced by interactions with

rays of sunlight — are com-

mon during the country’s wet

season. That’s when veils of

ice-crystal-laden cirrostratus

clouds (the type that usually

produces the halo phenom-

enon) often precede or follow

passing thunderstorms.

The February sighting

began with an enhancement of

the top of the 22° halo that

grew into the upper tangential

arc — an ice-crystal display

that curves outward from the

top of the halo, like the horns

of a bull. As the Sun rose, the

horns began dropping down

alongside the halo. Meanwhile,

the same phenomenon began

in reverse from the bottom of

the 22° halo, until the horns

merged into the circumscribed

bow. You can see these features

in the picture to the right.

Like the 22° halo, a circum-

scribed halo is created when

light passes through hexagonal

pencil (or column) crystals.

The difference is that the crys-

tals that form the 22° halo twirl

around three axes, whereas the

crystals that create the circum-

scribed halo f loat horizontally

rotating around two. As

described earlier, a circum-

scribed halo forms from the

union of the upper and lower

tangential arcs and is visible

when the Sun lies between 35°

and 55° above the horizon. The

image here shows its appear-

ance midway up the sky.

Symbols in the sky?

As I admired the warped-

looking ice-crystal complex,

including the orange interiors

of the rings and the fuzzy

bluish exteriors, my mind was

drawn to a photo I recently

shot while taking in the ancient

SECRETSKY

A Hathor halo?

A solar phenomenon could have inspired ancient Egyptians.

Egypt exhibit at the Ashmolean

Museum in Oxford, England.

One depiction in particu-

lar caught my attention: the

winged goddess Hathor, with

her telltale cow horns set in a

solar disk atop her head.

In ancient Egypt, the hiero-

glyph for the Sun is a circle

surrounded by a ring, which

some scholars have interpreted

as a 22° solar halo. Certainly

the ancients had also seen cir-

cumscribed halos and more.

The horns of Hathor are par-

ticularly interesting. They rep-

resent the Apis, a bull revered

in ancient Egypt as a fertility

god. The bull was also associ-

ated with the solar cult and

was often represented with the

Sun disk between his horns.

Isn’t it possible, then, that the

horns of Hathor were inspired

by the hornlike appendages of a

tangential arc — especially

since the halos can appear at

times when fertilizing rains are

either approaching or receding?

Now consider the following

eyelike appearance: the pupil of

the Sun surrounded by the iris

of the 22° halo and the lids of

the circumscribed halo. The

Eye of Ra, in fact, sometimes

functioned as the goddess

Hathor, and her Sun disk is

often represented as an eye

from which the Sun is born.

One hieroglyph of the Sun

incorporates two Uraeus cobras

coiled around the disk of the

Sun, looking like lobed append-

ages, similar to the appearance

of the circumscribed halo. Food

for thought?

As always, send your

thoughts (and observations)

to [email protected].

BY STEPHEN JAMES O’MEARA

A

BROWSE THE “SECRET SKY” ARCHIVE AT http://www.Astronomy.com/OMeara.

Occasionally, the 22° halo (the inner circle) coincides with the sighting of a

circumscribed halo. Both phenomena are caused by sunlight passing through

ice crystals in the upper atmosphere. STEPHEN JAMES O’MEARA

Stephen James O’Meara

is a globe-trotting observer

who is always looking for the

next great celestial event.

The Egyptian goddess

Hathor (left) has many

similarities to a lower

solar halo. Could the

real sky phenomenon

have influenced

Egyptian mythology?

STEPHEN JAMES O’MEARA

This ornament shows one of the Uraeus

cobras. The round disk represents the

Sun. WIKIMEDIA COMMONS