The oldest eclipse record is found on a clay tablet uncovered in the ancient city of Ugarit, (in what is now Syria), with two plausible dates usually cited: 3 May 1375 BC or 5 March 1223 BC, the latter being favored by most recents authors on the topic. It is certainly clear that by the eight century BC, the Babylonians were keeping a systematic record of solar eclipses, and may even have been able to predict them fairly accurately based on numerological rules.
Fotheringham, J.K. 1933, The Story of Hi and Ho, Journal of the British Astronomical Association, 43, 248-257.Zirker, J.B. 1995, Total Eclipses of the Sun, Princeton University Press.
Littman, M., Willcox, F., and Espenak, F. 2000, Totality: Eclipses of the Sun, 2nd ed., Oxford University Press.
The two oldest record of a sunspot observation are found in the Book of Changes, probably the oldest extant Chinese book, compiled in China around or before 800 BC. The text reads "A dou is seen in the Sun", and A mei is seen in the Sun". From the context, the words (i.e., chinese characters) "dou" and "mei" are taken to mean darkening or obscuration.
Astronomers at the court of the Chinese and Korean emperors made regular notes of sunspots, most less elliptical than the one cited above. It seems, however, that observations were not carried out systematically for their own sake, but instead took place whenever astrological prognostication was demanded by the emperor. The surviving sunspots records, though patchy and incomplete, covers nearly 2000 years and represents by far the most extensive pre-telescopic sunspot record.
Mossman, J.E., 1989, A comprehensive search for sunspots without the aid of a telescope, 1981-1982, in Quarterly J. R. Astr. Soc., 30, 59-73.Stephenson, F.R. 1990, Historical evidence concerning the Sun: interpretation of sunspot records during the telescopic and pre-telescopic eras, in Phil. Trans. R. Soc. London, A330, 499-512.
Hetherington, B. 1996, A chronicle of pre-telescopic astronomy, John Wiley and Sons.
This basic planetary arrangement formed the basis of mathematical model of planetary motion developed four centuries later by Claudius Ptolemy (ca. 100-170). In Aristotle's scheme there exist fundamental physical differences between the terrestrial and celestial realms, as demarcated by the Moon's sphere. Everything under the Moon is made of the four elements earth, water, air and fire, themselves arranged concentrically about the center of the universe. Pure circular motion prevail throughout the heavens, which are are made of an incorruptible fifth element (or "quintessence").
Grant, E. 1977, Physical Science in the Middle Ages, Cambridge University PressCrowe, M.J. 1990, Theories of the World from Antiquity to the Copernican Revolution, Dover.
Pedersen, O. 1993, Early Physics and Astronomy, revised ed., Cambridge University Press.
ca. 200 BC: The distance to the Sun
The first mathematically-based attempt at determining the Sun-Earth
distance is due to
Aristarchus of Samos
(ca. 310-230 BC).
The procedure followed by Aristarchus is illustrated on the diagram
below; form a triangle
by connecting the Earth (E), Sun (S) and Moon (M). At the first or third Moon
quarter,
the triangle so described in a right-angle triangle (a=90°). The
angle b can be measured by an observer on Earth,
which then allows the angle c to
be computed (c=90-b when a=90°). The ratio
of the Earth-Moon segment (EM) to the Earth-Sun segment (ES) is by definition
equal to sin(c) (in modern trigonometric parlance; Aristarchus expressed
this differently).
Aristarchus' geometric construction used to estimate the distance
to the Sun. The Earth-Sun-Moon triangle and sizes are not drawn to scale.
While sound in theory, in practice this procedure is highly inaccurate in the Earth/Sun/Moon case; this is because EM is much smaller than ES, implying that b is very close to 90°, so that c is in turn very small. This has the consequence that a small measurement error on b translates in a large variation in the ratio EM/ES (again in modern parlance, a measurement error db is amplified by a factor 1/(sin c)2, which is large when c is very small). Aristarchus measured b=87°, while the true value is in fact 89° 50 minutes. This may seem a small error, but because of the large error amplification Aristarchus' value leads to EM/ES=19, instead of the true value EM/ES=397. Nonetheless, Aristarchus' calculation was the first to mathematically set the spatial scale of the cosmos.
Van Helden, A. 1985, Measuring the Universe, University of Chicago Press.Hirschfeld, A.W. 2001, Parallax, Freeman.
While the solar corona is visible at any solar eclipse,
the first explicit mention of what can be pretty ambiguously interpreted
to be the corona was made by the Byzantine historian Leo Diaconus
(ca. 950-994),
as he observed the total eclipse of 22 December 968 from Constantinople
(now Istanbul, Turkey). His observation is preserved in the
Annales Sangallenses, and reads:
"...at the fourth hour of
the day ... darkness covered the earth and all the brightest stars
shone forth. And is was possible to see the disk of the Sun,
dull and unlit, and a dim and feeble glow like a narrow band shining
in a circle around the edge of the disk". Compare this description
to the modern eclipse photographs shown on
slides 9 and
slide 10 of the HAO slide set.
A much older possible description of the corona is said to be found
on engraved oracle bones dating from the Shang dynasty in China
(1766 to 1123 BC), but is far more ambiguous and open to interpretation
than Diaconus' description.
Hetherington, B. 1996, A chronicle of pre-telescopic astronomy,
John Wiley and Sons.
The accompanying text translates to something like:
"...from morning to evening, appeared
something like two black circles within the disk of the Sun,
the one in the upper part being bigger, the other in the lower part
smaller. As shown on the drawing." The facts that the Worcester
monks could apparently distinguish the umbrae and penumbrae of
the sunspots they observed suggests that the spots must have been
truly exceptionally large.
Large sunspots can be visible to the naked-eye under suitable
viewing conditions, for example when the sun is partially obscured
by clouds or mist, particularly at sunrise or sunset. Numerous such
sighting exist in the historical records, starting
with Theophrastus (374-287 B.C.) in the fourth century B.C.
However, by far the most extensive
pre-telescopic records are found in the far east,
especially in
the official records of the Chinese imperial courts,
starting in 165 B.C. In the West,
the dominating views of
Aristotle
concerning the incorruptibility of the heavens
meant that sunspots were "physically impossible", so that sightings
were ignored or ascribed to transit of Mercury or Venus across the
solar disk.
Van Helden, A. 1996, Galileo and Scheiner on sunspots, in
Proc. Am. Phil. Soc., 140, 358-396.
Prominences are large accumulation of (relatively) cold gas held
suspended high in the solar atmosphere by the Sun's magnetic field
(see
Slide 6 and
Slide 7 of the HAO slide set).
Large prominences are often visible at times of solar eclipses, in the
form of small reddish filaments or blobs in the lower corona.
The first fairly unambiguous description of prominences is usually taken
to be that found in the Russian Chronicle of Novgorod, in
the following description of the 1 May 1185 solar eclipse:
"In the evening there as an eclipse of the sun. It was getting very
gloomy and stars were seen ... The sun became similar in appearance to the
moon and from its horns came out somewhat like live embers."
Hetherington, B. 1996, A chronicle of pre-telescopic astronomy,
John Wiley and Sons.
Kuhn, T.S. 1957, The Copernican Revolution, Harvard University Press.
Boas, M. 1962, The Scientific Renaissance 1450-1630, Harper & Row
[Dover reprint available].
Gingerich, O. 1993, The Eye of Heaven,
New York: American Institute of Physics.
Grant, E. 1994, Planets, Stars, & Orbs. The Medieval Cosmos,
1200-1687, Cambridge University Press
Thoren, V.E. 1989, Tycho Brahe, in
The General History of Astronomy, vol. 2A, eds. R. Taton and C. Wilson,
Cambridge University Press, pps. 3-21.
Gingerich, O. 1989, Johannes Kepler, in
The General History of Astronomy, vol. 2A, eds. R. Taton and C. Wilson,
Cambridge University Press, pps. 54-78.
Gingerich, O., and Voelkel, J.R. 1998, Journal for the History
of Astronomy, 29, 1-34.
Physics.
The existence of ephemeral blemishes on the Sun's surface was
in stark conflict with the then prevailing
Ptolemaic/Aristotelian-based cosmology
endorsed by the Roman catholic Church (after suitable
modification to avoid open contradiction with the Scriptures).
Galileo's views on sunspots contributed significantly
the sequence of events that landed him in front of the
Roman Inquisition
in 1633. Officially, Galileo was condemned for disobedience to
the Church, in the context of his open
endorsement of the
Copernican heliocentric planetary model.
Growing animosity on
the part of the Jesuits who, in particular through their
chief astronomer Christopher Clavius
(1538-1612), had been originally quite supportive
of Galileo's early telescopic discoveries, also contributed
to Galileo's downfall.
Galileo, G. 1613, Letters on Sunspots [in S. Drake (trans.) 1957,
Ideas and Opinions of Galileo, Doubleday].
Galileo, G. 1632, Dialogues concerning the two chief world systems,
trans. S. Drake, 2nd edition 1967, University of California Press.
Mitchell, W.M. 1916, The history of the discovery of the solar
spots, in Popular Astronomy, 24, 22-ff.
Shea, W.R. 1970, Galileo, Scheiner, and the interpretation of
Sunspots, Isis, 61, 498-519.
Drake, S. 1978, Galileo at work: his scientific biography,
Chicago: The University of Chicago Press [1995 Dover reprint]
Aiton, E. J. 1989, The Cartesian Vortex Theory, in
The General History of Astronomy, vol. 2A, eds. R. Taton and C. Wilson,
Cambridge University Press, pps. 207-221.
Further Readings
on the history of solar physics.
Other Web Sites
with material on the history of solar physics.
968: The first mention of the solar corona
The solar corona is the hot, extended outer atmosphere of the Sun. It is far
too faint to be seen against the blinding brightness of the solar disk itself,
but becomes visible, and spectacularly so, at times of total solar
eclipses when the solar disk is obscured by the Moon.
References and further reading:
1128: The first sunspot drawing
This drawing, from the Chronicles of John of Worcester (one of the many
monks who contributed to the Worcester Chronicles), represents
to the best of our knowledge the first surviving sunspot drawing,
from a sighting on Saturday, 8 December 1128. Compare it with
the sunspots seen on
Slide 1 and
Slide 3 of the HAO slide set.
Sunspot drawing in the Chronicles of John of Worcester, twelfth
century. Notice the depiction of the penumbra around each spot.
Reproduced from R.W. Southern, Medieval Humanism,
Harper & Row 1970, [Plate VII].
References and further reading:
1185: The first description of solar prominences
References and further reading:
Sviatsky, D. 1923, Astronomy in the Russian Chronicles, Journal of the
British Astronomical Association, 33, 285-287.
1543: The Sun moves to center stage
The cosmos of the late Christian medieval era was a fusion of ideas
combining the physics of
Aristotle
and the planetary astronomy of
Ptolemy.
This is the world view that was destroyed in the sixteenth and
seventeenth centuries. The first blow was dealt by
Nicholas Copernicus (1473-1543),
who published his landmark book
De Revolutionibus Orbium Coelestium
in 1543. There Copernicus presented a
new planetary model
with the Sun placed in
center, and letting all planets (including the Earth) orbit
around the Sun. Copernicus also gave the Earth two additional motions:
a daily axial rotation, and a precession of that spin axis. In doing
so, Copernicus eliminated the need for
the two outermost spheres of the ptolemaic model
and produced a system where the speeds of revolution decrease
gradually outward all the way to the fixed stars.
The Copernican planetary model. The Sun is at the center of all
planetary motions, except for the Moon which orbits Earth. Under
this arrangement the orbital speed of planets decreases steadily
outwards, and the outer sphere of fixed stars is truly motionless.
In Copernicus' original model
the Earth has three motions: a daily 24-hr axial rotation, a yearly
orbital motion about the Sun, and a third motion, somewhat
related to precession
which Copernicus thought necessary to properly reproduce ancient
observations.
Copernicus ostensibly introduced his heliocentric model in order
to do away with equants and various motions previously
attributed to the sphere of fixed stars,
but it appears clear that he believed
in the physical reality of his heliocentric hypothesis. Because
Copernicus' model could be construed as yet another mathematical
device useful in astronomy but without physical reality, his model
could at first be used by astronomers without attracting
the ire of philosophers and theologians committed to the centrality
and fixity of the Earth.
This situation was to change in the next century.
References and further reading:
1609: The Sun in focus
An early convert to the Copernican system was
Johannes Kepler (1571-1630).
After ten years of laborious work using the accurate observations
of planetary positions accumulated over 20 years by the astronomer
Tycho Brahe (1546-1601),
Kepler came to realize that the orbital paths of planets has the form
of ellipses with the Sun at one focus, and that the radius vector
joining a given planet to the Sun sweeps equal areas in equal time
(today known as Kepler's first and second laws). In 1609 Kepler published
his landmark
Astronomia Nova,
and in 1619 his
Harmonice mundi,
where what is now known as Kepler's third law (orbital period squared
proportional to mean distance cubed) is first laid out.
Using his planetary model and Brahe's observations, Kepler produced
in 1627 the
Rudolphine Tables
of planetary positions. These proved more accurate, by over an order
of magnitude, than previous tables produced using
the original
planetary model of Copernicus.
References and further reading:
1610: First telescopic observations of sunspots
In the first decade of the seventeenth century, four
astronomers more or less simultaneously turned the newly invented
telescope toward the Sun, and noted the existence of sunspots.
They were
Johann Goldsmid
(1587-1616, a.k.a. Fabricius)
in Holland,
Thomas Harriot (1560-1621) in England,
Galileo Galilei (1564-1642)
in Italy, and the Jesuit
Christoph Scheiner (1575-1650) in Germany.
Reproduction of one of Galileo's sunspot drawings. The
umbrae/penumbrae structure is clearly depicted on this
June 23 1612 drawing.
To Harriot
belongs the oldest recorded sunspot
observation, on December 8 1610, as evidenced by
entries in his notebooks,
but he did not pursue these observations
in any systematic or continuous manner at the time.
Fabricius was the first to
publish his results in 1611, and
correctly interpreted the apparent motion of sunspots in
terms of axial rotation of the Sun.
Galileo and
Scheiner,
however, were the most active in using sunspots
to attempt to infer physical properties of the Sun.
To Galileo belongs the credit of making a convincing case that sunspots are
indeed features of the solar surface, as opposed to intra-Mercurial planets
(Scheiner's original position). Galileo's views were first laid out in detail
in his 1613
Letters on Sunspots,
written in response to Scheiner own views on the matter,
first published in 1612 under the pseudonym of Apelles in the form of
three letters
to Mark Welser (1558-1614),
Augsburg Magistrate, patron of science, and scientific
correspondent of both Scheiner and Galileo.
Some years later Scheiner, in his massive 1630 treatise on sunspots entitled
Rosa Ursina,
accepted the view of sunspots as marking on the solar surface and
used his accurate observations,
to infer the fact that the Sun's rotation axis
is inclined with respect to the ecliptic plane (i.e., the plane of the
Earth's orbit around the Sun).
References and further reading:
Galileo, G. 1610, Sidereus Nuncius, trans.
A. van Helden 1989, The University of Chicago Press.
1644: The Sun as a star
Detail of a diagram from the 1644 Principia philosophiae
of René Descartes,
depicting his conception of the cosmos as an aggregate
of contiguous vortices, most with a star at their center.
S is the Sun.
The
Copernican system
replaced the Earth by the Sun as the center
of the universe, but otherwise maintained a clear distinction
between the Sun, and the "fixed" stars, distributed on the
fixed, outermost sphere of the copernican cosmos. This last concession
to humanity's cosmic centrality
was rejected by the generation of copernicans following
Kepler and
Galileo.
Prominent among them was
René Descartes
(1596-1650) who, in his 1644 book Principia philosophiae,
put forth a
model of the cosmos
where the Sun is but one
of many star, each of which having formed at the center
of a primeaval vortex. Descartes viewed
sunspots as floating aggregates of etheral matter, accreted
along the Sun's rotational axis, where centrifugal forces
are negligible.
References and further reading:
Return to Sun Education page.
Return to HAO homepage.
-Written by paulchar@ucar.edu.
-Last revised 22 December 1999 by paulchar@ucar.edu.
Copyright 2000, NCAR. - Approved by Paul Charbonneau -