A Little Bit of (Naked Eye) Sun Spot History
It is only in the last 200 years that astronomers came to the conclusion that sun spots are concentrations of strong magnetic fields piercing the solar photosphere. Visually, they look like dark blemishes on the solar disk. Most sun spots are too small to be readily visible by naked eye observations, but some reach a size sufficient to be visible without a telescope, under suitable viewing conditions (for example, when the sun is partially obscured by fog or thick mist, or clouds). However, because of their possible astrological significances, reports of naked-eye sun spot observations are indeed to be found in many ancient chronicles and court chronologies.
From the year 28 B.C., comes the report "Heping reign period, 1st year, 3rd month, day Guiwei, the rising sun was yellow; a black gas was at the center of the sun, like a coin".
During the period from 28 B.C. to 1638 A.D. there are 112 descriptions of outstanding sun spots in the official Chinese histories.
It wasn't until the early 1600's that sun spot observations began in earnest, coinciding with the invention of the telescope. The first telescopic observation of the sun probably belongs to Thomas Harriot (1560-1621) on Dec 8th, 1610. He was one of four prominent observers at this time using telescopes to look at the sun. They were Johann Goldsmid (1587-1616, known as Fabricius) in Holland, Thomas Harriot in England, Galileo Galilei (1564-1642) in Italy, and the Jesuit Christoph Scheiner (1575-1650) in Germany. Fabricius is credited with associating sun spots with the axial rotation of the sun, a view which Galileo made the convincing case for. Galileo's views on sun spots contributed significantly the sequence of events that landed him in front of the Roman Inquisition in 1633, but growing animosity on the part of the Jesuits who, in particular through their chief astronomer Christopher Clavius (1538-1612), also contributed to Galileo's downfall. [Academic jealousy is nothing new!]
|Fabricius' de Maculis in Sole observatis et apparente earum cum Sole conversione, Narratio - Account of Spots observed on the Sun and of their apparent rotation with the Sun.||Reproduction of one of Galileo's sun spot drawings. The umbrae/penumbrae structure is clearly depicted on this June 23 1612 drawing.||A picture of Christoph Scheiner. Scheiner's original opinion was that sun spots were small planets closely orbiting the Sun.|
After this burst of discovery and observation, sun spot observation went
dormant for many years. In a letter to Humphrey Marshall dated, London, February
14, 1773, a Mr B. Franklin comments about the sun spot observations
Marshall had sent him
| ...The observations I communicated to our
astronomers of the Royal Society, who are much pleased with them, and hand
them from one to another; so that I have had little opportunity of
examining them myself, they not yet being returned to me.
Here are various opinions about the solar spots. Some think them vast clouds of smoke and soot arising from the consuming fuel on the surface, which at length take fire again on their edges, consuming and daily diminishing until they totally disappear. Others think them spots of the surface, in which the fire has been extinguished, and which by degrees is rekindled. It is remarkable, that, though large spots are seen gradually to become small ones, no one has observed a small spot gradually become a large one; at least I do not remember to have met with such an observation. If this be so, it should seem that they are suddenly formed of their full size; and perhaps, if there were more such constant and diligent observers as you, some might happen to be observing at the instant such a spot was formed, when the appearances might give some ground of conjecture by what means they are formed.
The professor of astronomy at Glasgow, Dr. Wilson, has a new hypothesis. It is this; that the sun is a globe of solid matter, all combustible perhaps but whose surface only is actually on fire to a certain depth, and all below that depth unkindled, like a log of wood, whose surface to half an inch deep may be burning coal, while all within remains wood. Then he supposes, by some explosion similar to our earthquakes, the burning part may be blown away, leaving bare the unkindled part below, which then appears as a spot, and only lessened as the fluid burning matter by degrees flows in upon it on all sides, and at last covers or rekindles it.
In 1857 Heinrich Schwabe was presented with the Gold Medal of the Royal Astronomical Society for his discovery of the sun spot cycle. He observed and recorded sun spots for 43 years and he found about a 10 year period in the appearance of the spots. This had not been noticed in 200 years of observing sun spots.
This work interested another man, Richard Carrington, so much that he also began to systematically observe sun spots between 1853 and 1861. He discovered that sun spots undergo a latitude drift. That is, that the average latitude of the spots decreases steadily from the beginning to the end of the solar cycle and get closer to the solar equator.
With the introduction of photographic studies of sun spots in the latter half of the 1800's, the old era of naked eye discovery on the Sun came to an end.
September 13, 2002Alisdair Davey email@example.com