man mathematician Christopher Cla- 
vius. Clavius, after whom a huge cra- 
ter on the moon is named, observed 
the eclipse from Rome. Despite mod- 
ern computations that indicate that 
this eclipse should have been total— 
although barely so — Clavius found 
that “a certain narrow circle was left 
on the Sun, surrounding the whole 
of the Moon on all sides.” He ap- 
parently did not mean the solar co- 
rona, which resembles a broad patch 
of light around the sun during a total 
eclipse, and he was familiar with what 
to expect since he had studied an ear- 
lier total eclipse in 1560. 
A bright ring of light is seen in 
an annular eclipse, that is, one that 
is not total because the moon is too 
I far out in its elliptical orbit to block 
out the whole sun. Eddy and Boor- 
nazian argued that the 1567 eclipse 
was annular for a different reason, 
namely, that the sun was bigger in 
1567 than allowed for by the com- 
putations, which are based on the mod- 
ern value of the solar diameter. 
Having witnessed several total 
eclipses of the sun myself, I was im- 
pressed by the above argument. In 
particular, I found it hard to accept 
a countersuggestion proposing that 
Clavius’s “circle” consisted of light 
from the bright innermost zone of the 
solar corona. No part of the corona 
has ever seemed bright enough to me 
to be mistaken for a part of the far 
more intense solar surface. However, 
there is an explanation of what Clavius 
saw that does not require so exotic 
a phenomenon as a shrinking of the 
sun. According to John Parkinson, an 
experienced solar astronomer at Uni- 
versity College, London, it is not suf- 
ficient to regard the edge of the moon 
as a circle of a certain size when you 
calculate the circumstances of a 
barely total eclipse. In such cases, you 
must allow for the topographic high 
and low spots around the lunar pe- 
riphery. 
Where there is a low spot on the 
moon’s edge, a bit of the bright solar 
surface may still shine through, al- 
though the eclipse is supposedly total. 
This phenomenon occurs for only an 
instant during an ordinary total 
eclipse, either just before or just after 
the phase of true totality. Eclipse view- 
ers call these momentary bright spots 
“Baily’s beads,” after a nineteenth- 
century English astronomer. Parkin- 
son reports that a recalculation of the 
1 567 eclipse, which takes the hills and 
valleys of the moon into account, has 
i yi . . . 
been done at the Royal Greenwich 
Observatory. The results reveal that 
the eclipse would have featured an 
extreme case of Baily’s beads, with 
a great many bright spots, like an 
outbreak of solar measles, all around 
the moon’s edge. Further, the bright 
spots would have persisted throughout 
the phase of totality, so that in a sense 
the eclipse was not truly total. This 
string of Baily’s beads might fairly 
have been called a “circle” by Clavius, 
who viewed the eclipse without a tele- 
scope. 
There remains one report of solar 
shrinkage for which there is not yet 
any seriously conflicting evidence. 
This finding, by five American, Aus- 
tralian, and English astronomers led 
by David W. Dunham of the Com- 
puter Sciences Corporation in Silver 
Spring, Maryland, and Sabatino Sofia 
of the Goddard Space Flight Center 
in nearby Greenbelt, is based on de- 
terminations of the width of the path 
of totality at solar eclipses in 1715, 
1976, and 1979. The 1715 eclipse was 
viewed from many locations in south- 
eastern England at the behest of Ed- 
mond Halley of comet fame. The Dun- 
ham and Sofia analysis of the English 
reports shows exactly where in the 
Kentish countryside the northern and 
southern edges of the path of totality 
went. 
There is no measurable difference 
in the determinations of the solar di- 
ameter from the 1976 and 1979 
eclipses, which is hardly surprising 
given the short interval between the 
two events. However, the width of the 
path of totality in 1715 implies a very 
slightly larger sun. Taken at face 
value, there was a decrease of about 
400 miles in the size of the sun over 
264 years. Although this shrinkage is 
so small as to be near the limit of 
detectability in the available data (but 
too small to be ruled out by the transit 
of Mercury measurements), it never- 
theless cannot have been under way 
over truly long periods of time. In 
fact, a shrinkage at this rate would 
reduce the sun to nothing in less than 
one million years. More likely, if the 
claimed shrinkage effect is indeed 
real, the sun must periodically reverse 
itself and slowly enlarge again. At 
least, let’s hope so. 
Stephen P. Maran is senior staff sci- 
entist in the Laboratory for Astron- 
omy and Solar Physics at NASA’s 
Goddard Space Flight Center in 
Greenbelt, Maryland. 
m 
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