S is for Sunspots, or One lucky scientist
It is common knowledge that Galileo's "discovery" of sunspots was one of the pivotal events that caused the sudden appearance of modern science. The sunspots suggested that the Sun and the heavens are corruptible, a tenet contrary to Aristotle (although accepted by many Stoics, patristic writers, and even theologians, e.g., by Cardinal Bellarmine). The discovery of the sunspots predates Galilean Copernicanism and it had the immediate and huge impact on the public opinion. The sunspots and irregularities on the surface of the Moon contradicted Aristotle's tenet that the moon and the heavens are permanent, perfect, and made of aether (also called quinta essentia, the stuff of the philosopher's stone). [For "chymistry" it was a decisive, mortal blow: if even the Sun is not made of the quintessence, then what is?] The body made of the perfect element was perfect, and the circle is perfect. The Sun is perfect and thus it moves around the Earth in a circle. It was a pretty clever theory that lasted for hundreds of years; and then came Galileo with his stupid sunspots and ruined everything. Few people realize, however, how unbelievably fortunate Galileo was. If the telescope were invented just 30 years later, he would not make his amazing "discovery" that dealt such a decisive blow to the peripatetic school. The mountains on the Moon were not as damning, because even Aristotle assumed that the part of the Moon that permanently faces the Earth might be corruptible (that's where the meteorites are from). It had to be the Sun. Here are some details, taken from this site.
...Sunspots are dark areas of irregular shape on the surface of the Sun...Records of naked-eye sunspot observations in China go back to at least 28 BCE. In the West, the record is much more problematical. It is possible that the Greek philosopher Anaxagoras observed a spot in 467 BCE, and it appears that there are a few scattered mentions in the ancient literature as well. However, in the dominant Aristotelian cosmology, the heavens were thought to be perfect and unchanging. A spot that comes and goes on the Sun would mean that there is change in the heavens. A very large spot seen for no less than eight days in 807 was simply interpreted as a passage of Mercury in front of the Sun. Other mentions of spots seen on the Sun were ignored.
...In 1607 Johannes Kepler wished to observe a predicted transit of Mercury across the Sun's disk, and on the appointed day he projected the Sun's image through a small hole in the roof of his house (a camera obscura) and did indeed observe a black spot that he interpreted to be Mercury.
...The scientific study of sunspots in the West began after the telescope had been brought into astronomy in 1609...Galileo and Thomas Harriot were the first, around the end of 1610; that Johannes and David Fabricius and Christoph Scheiner first observed them in March 1611, and that Johannes Fabricius was the first to publish on them.
Sunspots (Rosa Ursina, Scheiner, 1630)
...Galileo had shown sunspots to a number of people in Rome during his triumphant visit there in the spring of 1611...[He] did not undertake a study of sunspots until April 1612. Scheiner began his serious study of spots in October 1611 and his first tract on the subject appeared in January 1612...Scheiner argued that sunspots were satellites of the Sun. They appeared as black spots when they passed in front of the Sun but were invisible at other points in their orbits. Their orbits had to be very close to the Sun for their shapes were foreshortened as they approached its edge. Scheiner observed sunspots through a telescope equipped with colored glasses.
...In April 1612, Galileo turned his attention to sunspots with the help of his protégé Benedetto Castelli, who was in Florence at the time. It was Castelli who developed the method of projecting the Sun's image through the telescope, a technique that made it possible to study the Sun in detail even when it was high in the sky. Galileo wrote his first letter to Welser on sunspots, in which he argued that spots were, in fact, on the surface of the Sun or in its atmosphere, and although he could not say for certain what they were, they appeared to him most like clouds...[Galileo observed how the spots rotated with the Sun - S.] Scheiner commented that his observations agreed precisely with those of Galileo and defended his judgment that sunspots were solar satellites. He showed a large number of sunspot observations, made at roughly the same time of the day, so that the Sun's orientation was the same and the motion of the spots across its disk could be easily followed.
...Galileo noticed that, while a spot took about 14 days to cross from one side of the Sun to the other, its rate of motion was by no means uniform. That is, the spot's motion always appeared much slower when near the edge of the Sun than when near the center. This Galileo recognized as an effect of foreshortening. That is, a spot coming around the limb is actually traveling towards you. But your eyes can't see the 3-D effect, and the spot likes as if it were moving slowing across the disk. However, when the spot is in the middle 1/3 or so of the Sun, all its motion is across the disk. So it appears to be moving quickly. Foreshortening would result if, and only if, the spot were on or very near the surface of the Sun. A planet orbiting the Sun would not appear to change its speed when moving across the Sun's disk.
...His definitive sunspot studies were followed up by others. In France Pierre Gassendi made numerous observations (not published until 1658); in Gdansk Johannes Hevelius (1647) and in Bologna Giovanni Battista Riccioli (1651) did the same. There is, therefore, a reasonably good sunspot record for the years 1610-1645...After this time, however, sunspot activity was drastically reduced. When, in 1671, a sunspot was observed, it was treated as a rare event. Sunspot activity increased again after about 1710.
...The Maunder Minimum is the name given to the period roughly from 1645 to 1715 A.D., when sunspots became exceedingly rare, as noted by solar observers of the time...During one 30-year period within the Maunder Minimum, for example, astronomers observed only about 50 sunspots, as opposed to a more typical 40,000-50,000 spots...The Maunder Minimum coincided with the middle - and coldest part - of the so-called Little Ice Age, during which Europe and North America, and perhaps much of the rest of the world, were subjected to bitterly cold winters...Whether there is a causal connection between low sunspot activity and cold winters is the subject of ongoing debate...The lower solar activity during the Maunder Minimum also affected the amount of cosmic radiation reaching the Earth. The resulting change in the production of carbon-14 during that period caused an inaccuracy in radiocarbon dating until this effect was discovered. Other historical sunspot minima have been detected either directly or by the analysis of carbon-14 in ice cores or tree rings; these include the Sporer Minimum (1450-1540), and less markedly the Dalton Minimum (1790-1820). In total there seem to have been 18 periods of sunspot minima in the last 8,000 years, and studies indicate that the sun currently spends up to a quarter of its time in these minima. Wikipedia
Scheiner never conceded his theory, but he, unlike Galileo, was very systematic and made many contributions to the studies of solar physics. Scheiner's method of illustrating the motion of individual spots across the face of the Sun became the standard way of rendering this motion and the changing shapes of the spots. Observe that if the planet is in a VERY low orbit, then foreshortening would also occur; that was Scheiner's point exactly. Extrasolar planets known as "hot Jupiters" discovered over the last 10 years are in very tight orbits around their suns (8-10 times closer than Mercury); the situation envisaged by Schreiner is possible. However, having hundreds of such planets, constantly appearing and disappearing, was an absurd idea. Galileo had a point there. However, if there were very few sunspots, such an argument would not have much currency. And this number was indeed very low after 1645.
What does it all mean? Galileo and Scheiner were very, very lucky. The telescope was invented when the solar activity was maximum (it cycles every 11 years) and if it were invented 30 years later, no sunspots would be found. What course would the events take in such a case? Would the teachings of Aristotle be taught for another 50 years or more?
PS: Maundler Minima occur roughly every 440 years on an irregular pattern and we may have the next one in 10-20 years, for all we know. Then another Little Ice Age could be upon us:
...Experts disagree on the duration of the Little Ice Age. Some mark its inception as early as the 1200s, others view the Little Ice Age "proper" as beginning around 1450 or even later. Low activity from 1645 to 1715, called the Maunder Minimum, matched perfectly one of the coldest spells of the Little Ice Age. Disagreements arise because the phenomenon was not simply a giant cold snap. The cooling trend began at different times in different parts of the world and often was interrupted by periods of relative warmth. All agree, however, that it lasted for centuries, and that the world began emerging from its grip between 1850 and 1900.
May be it was not only Galileo who was lucky?
...Sunspots are dark areas of irregular shape on the surface of the Sun...Records of naked-eye sunspot observations in China go back to at least 28 BCE. In the West, the record is much more problematical. It is possible that the Greek philosopher Anaxagoras observed a spot in 467 BCE, and it appears that there are a few scattered mentions in the ancient literature as well. However, in the dominant Aristotelian cosmology, the heavens were thought to be perfect and unchanging. A spot that comes and goes on the Sun would mean that there is change in the heavens. A very large spot seen for no less than eight days in 807 was simply interpreted as a passage of Mercury in front of the Sun. Other mentions of spots seen on the Sun were ignored.
...In 1607 Johannes Kepler wished to observe a predicted transit of Mercury across the Sun's disk, and on the appointed day he projected the Sun's image through a small hole in the roof of his house (a camera obscura) and did indeed observe a black spot that he interpreted to be Mercury.
...The scientific study of sunspots in the West began after the telescope had been brought into astronomy in 1609...Galileo and Thomas Harriot were the first, around the end of 1610; that Johannes and David Fabricius and Christoph Scheiner first observed them in March 1611, and that Johannes Fabricius was the first to publish on them.
Sunspots (Rosa Ursina, Scheiner, 1630)
...Galileo had shown sunspots to a number of people in Rome during his triumphant visit there in the spring of 1611...[He] did not undertake a study of sunspots until April 1612. Scheiner began his serious study of spots in October 1611 and his first tract on the subject appeared in January 1612...Scheiner argued that sunspots were satellites of the Sun. They appeared as black spots when they passed in front of the Sun but were invisible at other points in their orbits. Their orbits had to be very close to the Sun for their shapes were foreshortened as they approached its edge. Scheiner observed sunspots through a telescope equipped with colored glasses.
...In April 1612, Galileo turned his attention to sunspots with the help of his protégé Benedetto Castelli, who was in Florence at the time. It was Castelli who developed the method of projecting the Sun's image through the telescope, a technique that made it possible to study the Sun in detail even when it was high in the sky. Galileo wrote his first letter to Welser on sunspots, in which he argued that spots were, in fact, on the surface of the Sun or in its atmosphere, and although he could not say for certain what they were, they appeared to him most like clouds...[Galileo observed how the spots rotated with the Sun - S.] Scheiner commented that his observations agreed precisely with those of Galileo and defended his judgment that sunspots were solar satellites. He showed a large number of sunspot observations, made at roughly the same time of the day, so that the Sun's orientation was the same and the motion of the spots across its disk could be easily followed.
...Galileo noticed that, while a spot took about 14 days to cross from one side of the Sun to the other, its rate of motion was by no means uniform. That is, the spot's motion always appeared much slower when near the edge of the Sun than when near the center. This Galileo recognized as an effect of foreshortening. That is, a spot coming around the limb is actually traveling towards you. But your eyes can't see the 3-D effect, and the spot likes as if it were moving slowing across the disk. However, when the spot is in the middle 1/3 or so of the Sun, all its motion is across the disk. So it appears to be moving quickly. Foreshortening would result if, and only if, the spot were on or very near the surface of the Sun. A planet orbiting the Sun would not appear to change its speed when moving across the Sun's disk.
...His definitive sunspot studies were followed up by others. In France Pierre Gassendi made numerous observations (not published until 1658); in Gdansk Johannes Hevelius (1647) and in Bologna Giovanni Battista Riccioli (1651) did the same. There is, therefore, a reasonably good sunspot record for the years 1610-1645...After this time, however, sunspot activity was drastically reduced. When, in 1671, a sunspot was observed, it was treated as a rare event. Sunspot activity increased again after about 1710.
...The Maunder Minimum is the name given to the period roughly from 1645 to 1715 A.D., when sunspots became exceedingly rare, as noted by solar observers of the time...During one 30-year period within the Maunder Minimum, for example, astronomers observed only about 50 sunspots, as opposed to a more typical 40,000-50,000 spots...The Maunder Minimum coincided with the middle - and coldest part - of the so-called Little Ice Age, during which Europe and North America, and perhaps much of the rest of the world, were subjected to bitterly cold winters...Whether there is a causal connection between low sunspot activity and cold winters is the subject of ongoing debate...The lower solar activity during the Maunder Minimum also affected the amount of cosmic radiation reaching the Earth. The resulting change in the production of carbon-14 during that period caused an inaccuracy in radiocarbon dating until this effect was discovered. Other historical sunspot minima have been detected either directly or by the analysis of carbon-14 in ice cores or tree rings; these include the Sporer Minimum (1450-1540), and less markedly the Dalton Minimum (1790-1820). In total there seem to have been 18 periods of sunspot minima in the last 8,000 years, and studies indicate that the sun currently spends up to a quarter of its time in these minima. Wikipedia
Scheiner never conceded his theory, but he, unlike Galileo, was very systematic and made many contributions to the studies of solar physics. Scheiner's method of illustrating the motion of individual spots across the face of the Sun became the standard way of rendering this motion and the changing shapes of the spots. Observe that if the planet is in a VERY low orbit, then foreshortening would also occur; that was Scheiner's point exactly. Extrasolar planets known as "hot Jupiters" discovered over the last 10 years are in very tight orbits around their suns (8-10 times closer than Mercury); the situation envisaged by Schreiner is possible. However, having hundreds of such planets, constantly appearing and disappearing, was an absurd idea. Galileo had a point there. However, if there were very few sunspots, such an argument would not have much currency. And this number was indeed very low after 1645.
What does it all mean? Galileo and Scheiner were very, very lucky. The telescope was invented when the solar activity was maximum (it cycles every 11 years) and if it were invented 30 years later, no sunspots would be found. What course would the events take in such a case? Would the teachings of Aristotle be taught for another 50 years or more?
PS: Maundler Minima occur roughly every 440 years on an irregular pattern and we may have the next one in 10-20 years, for all we know. Then another Little Ice Age could be upon us:
...Experts disagree on the duration of the Little Ice Age. Some mark its inception as early as the 1200s, others view the Little Ice Age "proper" as beginning around 1450 or even later. Low activity from 1645 to 1715, called the Maunder Minimum, matched perfectly one of the coldest spells of the Little Ice Age. Disagreements arise because the phenomenon was not simply a giant cold snap. The cooling trend began at different times in different parts of the world and often was interrupted by periods of relative warmth. All agree, however, that it lasted for centuries, and that the world began emerging from its grip between 1850 and 1900.
May be it was not only Galileo who was lucky?