Astronomy - June 2015

(Jacob Rumans) #1
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 rosenfel@chass.utoronto.ca,
and be sure to copy me at
sjomeara31@gmail.com.

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)

Free download pdf