Historical sunspots
1: The drawing by John of Worcester, from 8 December AD 1128 (Corpus Christi College, Oxford).
2: A cluster of sunspots (RGO 50/13054).
The earliest drawing of sunspots
he Latin Chronicle of John of Worcester
(Darlington et al. 1995, McGurk 1998),
which covers the period from earliest
times to AD 1140, contains a number of
records of celestial phenomena. These include
eclipses of Sun and Moon, comets, meteor
showers and aurorae. One of the most interesting of these reports is a description of two
sunspots which were seen on 8 December in
AD 1128. In the solitary manuscript which contains this account, the text is accompanied by a
colourful drawing (albeit somewhat idealized)
showing the positions of the two spots on the
solar disk. This would appear to be the earliest
known illustration of sunspots, despite the fact
that they had already been recorded in China
for many centuries prior to that date. From
ancient times in China, the symbol for the Sun
was a red disk containing a representation of a
large crow. This symbol may well owe its origin to sunspots, but no Chinese drawing which
depicts discrete solar spots exists until after
AD 1400. It further appears that no subsequent
illustration of sunspots survives until after the
invention of the telescope.
T
Unaided eye observations of sunspots
Sunspots are by no means among the most
spectacular of celestial events. However, if the
Sun is dimmed by thin cloud, haze etc, large
sunspots (or spot groups) may become readily
visible to the unaided eye (Mossman 1989). In
the pre-telescopic period, by far the most consistent observers of sunspots were the Chinese
and Korean astronomers who recorded more
than 150 separate sightings – the earliest in
165 BC (Wittmann and Xu 1987, Stephenson
and Yau 1988). Analysis of these early observations provides some indication of long-term
solar variability (Stephenson 1990).
The East-Asian astronomers do not appear to
have used any artificial aid to reduce the Sun’s
December 1999 Vol 40
F Richard Stephenson and David
M Willis describe and discuss a
drawing of sunspots from the 12th
century – the earliest known.
unspots are among celestial
phenomena recorded by early
observers; descriptions feature in
European and Chinese recordings.
We report here on a drawing of
sunspots that is their first known
illustration, and comes from
Worcester, England. It predates the
first known Chinese drawings (from
the 15th century) and there appear
to be no later drawings until the
invention of the telescope.
S
glare, instead taking advantage of favourable
atmospheric conditions. Their observations are
largely reported in the official histories of both
countries. The usual description notes that “a
black spot” or “a black vapour” was seen in the
Sun. Sometimes several spots were said to be
visible at the same time – often for a few days.
Occasionally discrete shapes were discerned.
For example, in AD 188 Chinese astronomers
recorded that “The Sun was orange in colour;
within it there was a black vapour like a flying
magpie” (Wittmann and Xu 1987, Stephenson
and Yau 1988). In AD 299 a sunspot was said
to resemble a flying swallow.
Between AD 840 and 1130, medieval Arab
astronomers very occasionally noted sunspots
(Goldstein 1969). However, influenced by the
Aristotelian notion of a faultless Sun, they
explained these spots away as transits of the
planets Venus or Mercury across the solar disk.
Mercury (apparent diameter no more than
about 12 arcsec) is much too small to be detected by the unaided eye when in transit. Although
Venus (apparent diameter approximately
60 arcsec) can certainly be seen under similar
circumstances (Goldstein 1969), transits of this
planet are extremely rare, occurring only about
once in a typical century. When modern computations of past Venus transits (Meeus 1958)
are compared with the Arab records, they
reveal that no such event was involved on any
of the dates indicated (Stephenson 1990).
Hence sunspots may be inferred in each case.
Only four or five European sightings of
sunspots were recorded before the late 16th
century; these range in date from AD 807 to
1371. All observations were recorded by chroniclers rather than astronomers. Chroniclers frequently had an appreciable interest in celestial
events. However, these men kept only a sporadic watch on the sky and in general noted the
more spectacular phenomena, such as eclipses
and comets. This would seem to be the most
likely explanation of why sunspot sightings are
so rare in pre-Renaissance Europe. The earliest
European account of a sunspot dates from
AD 807 (Wittmann and Xu 1987). This was
recorded in a German chronicle, Annales Loiselanos. The account was translated by Newton
(1972) as follows: “807... The star Mercury on
the 16th calends April (= 17 March) was seen in
the Sun like a small black spot, a little above the
centre of that body, and it was seen by us for
eight days, but when it first entered, and when
it left, clouds kept us from observing.” The
lengthy period of visibility implies a sunspot
interpretation; a transit of Mercury lasts only a
few hours. Computation shows that the planet
was about 15° from the Sun at this time, while
Venus was even further away. Eight days
6.21
Historical sunspots
(between one-quarter and one-third of a solar
rotation) is, of course, a quite feasible duration
for the visibility of a sunspot.
After AD 1128, the record of which is the main
subject of this paper, according to the
Niconovsky and other chronicles, dark spots
were seen on the Sun in Russia during the summer of both AD 1365 and 1371 (Vyssotsky
1949). On the latter occasion the description
was quite graphic: “There were dark spots on
the Sun as if nails were driven into it.” Both of
the Russian observations were made at the time
of forest fires, the smoke from which would substantially dim the Sun. Under similar circumstances in Bohemia in AD 1139, it was recorded
that “some people had seen a fissure in the Sun”,
a description which may possibly imply sunspots
(Wittmann and Xu 1987). After AD 1371, no
other sunspot sighting is known to have been
reported by a European observer until AD 1590.
The record by John of Worcester
The chronicle of John of Worcester was compiled during the first half of the 12th century.
The most important manuscript of this chronicle is in the archives of Corpus Christi College,
Oxford (MS 157). For the period from
AD 1128 to 1140, this manuscript contains
much unique information and is possibly written in the hand of John of Worcester himself
(Darlington et al. 1995 pp. xxi, xxix–xxxiv;
McGurk 1998 p. xix).
The entry describing the sunspot, as translated
by McGurk (1998 p183), is as follows:
“[1128]... In the third year of Lothar, emperor of
the Romans, in the twenty-eighth year of King
Henry of the English, in the second year of the
470th Olympiad, seventh indiction, twenty-fifth
moon, on Saturday, 8 December, there appeared
from the morning right up to the evening two
black spheres against the Sun (quasi due nigre
pile infra solis orbitam). The first was in the
upper part and large, the second in the lower
and small, and each was directly opposite the
other as this diagram shows” (Corpus Christi
College MS 157, folio 380: lower half).
The date is firmly established. Lothar (later
Holy Roman Emperor), became King of Germany in May of AD 1125, so that his third
(full) year was 1128. Henry (I) of England was
crowned in August of AD 1100, so that his
28th (full) year also corresponded to AD 1128.
The year is also confirmed by the mention of
the seventh indiction. The first year of the then
current indiction (a 15-year fiscal period)
began on 1 September in AD 1122. However,
John of Worcester has miscalculated by 26
years when giving the date in terms of the
Olympiads. The 2nd year of the 470th
Olympiad (each year of which commenced in
the summer) was AD 1102/3; the year
AD 1128/9 was the 4th year of the 476th
Olympiad. A date in 1128 is confirmed by the
6.22
fact that 8 December in that year was indeed a
Saturday. John has also made a mistake in giving the day of the lunar month; 8 December
was the 15th rather than the 25th. This discrepancy could be the result of a scribal error,
or simply due to lack of the necessary astronomical knowledge – not uncommon among
medieval European chroniclers.
On 8 December in AD 1128, Venus and Mercury were about 15° from the Sun, on opposite
sides. Hence although the sunspots were only
seen on a single day, a planetary transit can
again be ruled out. There was no Venus transit
between AD 1040 and 1153.
The drawing in the manuscript of the chronicle of John of Worcester, which was first published by Darlington et al. (1995 p. xxxiii), is
shown in figure 1. This is surrounded by the
Latin text, most of which describes the
sunspots. The artistic adornment in figure 1
(particularly of the sunspots themselves) hinders a proper scientific interpretation of the
drawing. However, it should be noted that the
main visual features of the sunspots (heliographic positions and relative sizes) are in good
agreement with the details recorded in the surrounding text.
To obtain an approximate quantitative estimate of the sizes of the two sunspots, it is
assumed that the areas coloured black represent the total (umbral plus penumbral) areas of
the sunspots and that the outermost (red) circle
represents the solar limb. With these assumptions, the angular diameters of the sunspots in
the northern and southern hemispheres of the
Sun are about 3 arcmin and 2 arcmin, respectively. The minimum diameter of a sunspot
that can be detected by the human eye without
the aid of a telescope is almost certainly less
than 1 arcmin (for further details see Willis et
al. 1996). Therefore, with the implicit assumption that figure 1 was drawn approximately to
scale, the black sunspots depicted in this drawing would have been easily observable with the
unaided eye. Figure 2 presents a photograph
from the original Royal Greenwich Observatory (RGO) solar plate for 16 May 1951 (RGO
50/13054) for comparison. This RGO photograph confirms that large, and comparatively
compact, sunspot groups can certainly exist,
although they occur more frequently during
times of strong solar activity.
At Worcester in early December, the Sun
(declination –22°) would attain an altitude of
no more than 15° at noon. Under favourable
atmospheric conditions, the low solar altitude
would probably assist continued observation
of the spots throughout the day. There is no
indication as to the time of day when the drawing was made. The position angle of the solar
axis as viewed from Worcester (latitude 52°)
would vary considerably during the course of
the day. Around noon, the axis would be
roughly perpendicular to the horizon but at
sunrise the tilt would be about 45°. Assuming
a fairly careful drawing, the indicated range in
heliographic latitude of the two spots is
between about 25° and 35°. However, ample
allowance should be made for artistic licence.
For a roughly contemporaneous example, see
the many drawings of the large partial solar
eclipse of 26 January AD 1153 in the various
chronicles of the monastery of Erfurt in Germany (Stephenson 1997 fig. 11.9).
There are no reports of sunspots from East
Asia in AD 1128, but two independent Chinese
accounts relate that on 22 March of the following year “within the Sun there was a black spot”
(Wittmann and Xu 1987, Stephenson and Yau
1988). It may well be significant that the Chinese observations occurred approximately four
solar rotation periods after the English sighting.
Two further Chinese sunspot records date from
AD 1131, but the phase of the solar cycle around
this time cannot be inferred with any confidence
solely from these few sunspot observations.
Conclusion
Despite the long tradition of observing spots
on the Sun in East Asia, it is of some significance that the earliest known drawing showing
sunspots – dating from AD 1128 – is from
Europe (and in particular England). Furthermore this is the work of a chronicler, not an
astronomer. The Worcester scribe deserves
commendation both for his careful written
record and also his efforts to depict what he
observed. It is regrettable that so few other pretelescopic drawings of sunspots survive. ●
F Richard Stephenson, Department of Physics,
University of Durham, and David M Willis,
Department of Physics, University of Warwick. We
are grateful to the President and Fellows of Corpus
Christi College, Oxford for permission to publish
figure 1. Figure 2 is reproduced, with permission,
from the collection of the former Royal Greenwich
Observatory. We are especially grateful to Prof.
John H Parkinson for several helpful comments.
References
Darlington R R et al. 1995 The Chronicle of John of Worcester Vol. II
Clarendon Press, Oxford.
Goldstein B R 1969 Centaurus 14 49–59.
McGurk P 1998 The Chronicle of John of Worcester Vol. III Clarendon
Press, Oxford.
Meeus J 1958 J. Br. astr. Assn. 68 98–108.
Mossman J E 1989 QJRAS 30 59–64.
Newton R R 1972 Medieval chronicles and the rotation of the Earth
Johns Hopkins Univ. Press, Baltimore, 393.
Stephenson F R 1990 Phil. Trans. Roy. Soc. A 330 499–512.
Stephenson F R 1997 Historical eclipses and Earth’s rotation
Cambridge University Press, Cambridge.
Stephenson F R and Yau K K C 1988 QJRAS 29 175–197.
Vyssotsky A N 1949 Meddelanden fran Lunds Astronomiska
Observatorium Ser II, No. 126: Historical Papers, No. 22.
Willis D M et al. 1996 QJRAS 37 189–229.
Wittmann A D and Xu Zhentao 1987 Astron. Astrophys. Suppl. Ser.
70 83–94.
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