Astronomy - June 2015

18 ASTRONOMY • JUNE 2015

I

n January 2015, I received

an email from Randall A.

Rosenfeld, archivist for

the Royal Astronomical

Society of Canada, ask-

ing for help from Astronomy

readers. The issue deals with a

12th-century rendering of what

is now generally accepted as the

earliest surviving depiction of

sunspots. And you may be able

to help verify a key aspect of

this stylized drawing.

Interpretation

The drawing exists in a 12th-

century manuscript of a Latin

chronicle attributed to “John

of Worcester,” who made the

observation December 8, 1128,

from England. Of it, he wrote,

“... from morning till the time

of vespers there appeared as it

SECRETSKY

A 12th-century

sunspot enigma

Is this feature observation or decoration?

were two dark balls below the

orbit of the Sun. One, which

was the larger, in the upper

part, and the other, which was

smaller, in the lower part.”

As Rosenfeld explains in the

October 2014 Journal of the

Royal Astronomical Society of

Canada, the two dark balls

were not actually beneath the

Sun. “The Sun was placed in

the realm of objects not subject

to change and corruption,” he

says. “Spots could not mar the

solar surface by occurring on it,

but they could be sublunary

objects in orbits beneath the

Sun seen against its surface

from the Earth.”

If this is the case, then the

depictions may be remarkable

in that they show a clear dis-

tinction between each spot’s

BY STEPHEN JAMES O’MEARA

umbra (the dark inner part) and

penumbra (the light outer

region) — namely, they appear

as black balls surrounded by

concentric red circles; each

outer circle is stylized.

While we can interpret the

colored circles surrounding the

black spots as penumbral

regions, Rosenfeld says, other

alternatives exist: They could be

mere decorative features typical

of 12th-century iconography, or

their representations also could

be decorative features that carry

observational information.

“The problem is that the

visual conventions of the artist

are not our visual conventions,”

Rosenfeld explains, “and the

rarity of the image, and the

paucity of mid-12th-century

solar cartographic legends set

us at a disadvantage. The pas-

sage of nine centuries is hard to

overcome!”

A visual challenge

Rosenfeld wonders if it is pos-

sible to clearly detect the differ-

ence between penumbral and

umbral regions of great sun-

spots when observing with the

naked eye (suitably protected)

or by pinhole or other forms of

projection. And thus he is ask-

ing us to help.

Today, people often see

naked-eye sunspots through

safe optical filters. Occasionally,

a person can observe a sunspot

when fog, haze, or other atmo-

spheric contaminants greatly

reduce our star’s glare, particu-

larly near sunset.

In a 1992 Quarterly Journal

of the Royal Astronomical

Society, H. U. Keller (Zurich

Observatory) and T. K. Friedli

(Sun Observer Group of Swiss

Astronomical Society) reported

on sunspot sightings based on

observations of naked-eye spots

from 20 observers.

They determined that an

average eye can see a sunspot

with a penumbral diameter of

at least 41 arcseconds and an

umbral diameter of at least 15

arcseconds. However, the

authors also say, “The observ-

ers themselves were, of course,

not able to distinguish between

umbra and penumbra.”

But the absence of evidence

is not evidence of absence. How

many of those same observers

would have seen penumbral

shadings had they been asked

to look? Also, were any of the

observed spots parts of exceed-

ingly large groups?

Rosenfeld considers the pos-

sibility of detecting penumbrae

via pinhole projection because

pinhole cameras in medieval

Europe survived from the cen-

tury after John of Worcester

and from earlier in the Middle

East. “There may very well be a

medieval account which may

suggest that solar surface detail

(a very prominent sunspot) was

detectable by means of a pin-

hole camera,” Rosenfeld says.

Rosenfeld is eager to hear

what you have to report based

on your observations and espe-

cially welcomes what you see

when you use pinhole projec-

tion. You can contact Rosenfeld

at [email protected],

and be sure to copy me at

[email protected].

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

Is this the earliest surviving

illustration of sunspots? This

carefully executed sketch is a

copy of the original illustration.

The copyist used a quill pen

and executed the drawing on

bovid parchment. RANDALL A.

ROSENFELD, AFTER JOHN OF WORCESTER

NASA’s suite of

climate space-

craft verify 2014

as the hottest

year since tem-

perature records

began in 1880,

ever so slowly

lowering the list

of known habit-

able Earth-like

planets to less

than one.

Vital signs

COSMIC WORLD

A look at the best and the worst that astronomy and

space science have to offer. by Eric Betz

Cold as

space

Supernova

hot

Astronaut Leland

Melvin, a former

NFL player, chem-

ist, and engineer,

gets online awws

for sneaking his

rescue dogs into

his NASA portrait.

Those may be the

only pups with

an accurate view

of their owner’s

awesomeness.

Proud pooches

Hubble spots a

cosmic smiley

face. The eyes are

two bright orange

galaxies and light-

bending gravity in

the galaxy cluster

forms the smile,

proving that E.T.

exists and, unlike

that creepy face

on Mars, wants us

to be happy.

Entropy happens

Worms with

freshly severed

heads and tails

are sent to the

space station for

astronauts to

study organ

regeneration in

orbit. Some-

where, NASA is

staffing a room

full of 10-year-

old boys.

Child labor

NASA GODDARD SPACE FLIGHT CENTER (VITAL SIGNS); NASA (CHILD LABOR, PROUD POOCHES); NASA/ESA, ACKNOWLEDGEMENT: JUDY SCHMIDT (ENTROPY HAPPENS)