Sunspots: 17th Century

April 5, 2009, 8:28 pm
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Introduction - Early 1600's

Using telescopes similar to Galileo Galilei’s instrument, Johannes Fabricius and Christoph Scheiner began the first systematic study of sunspots in early 1611. Johannes Fabricius was the first to publish his observations in De Maculis in Sole Observatis ("On the Spots Observed in the Sun") in 1611, but it remained unknown to the other observers for some time. Scheiner’s book Tres Epistolae de Maculis Solaribus Scriptae ad Marcum Welserum  ("Three Letters on Solar Spots written to Marc Welser") appeared in 1612.

Scheiner wanted to preserve the unblemished perfection of the sun, and proposed that sunspots were simply satellite orbiting the sun. In 1612, Galileo was equally certain that sunspots were on the surface of the sun, or at least that they could be clouds in the solar atmosphere, and published his first drawings of them in his 1613 book Istoria e Dimostrazioni intorno alle Macchie Solari  (Letters on Sunspots to Marc Welser), which was basically an answer to Scheiner’s hypothesis. After a series of lengthy letter exchanges and debates, Scheiner eventually backed away from his assertion of solar satellites, and Galileo’s interpretation prevailed. [1]

One of Galileo's sunspot "plates" published in 1613. (Source: Univ. of Oklahoma, History of Science.)Galileo’s separate drawings for each day were printed on separate pages, one of which is pictured at left. You can browse Galileo’s sunspot observations for 28 days, they are superimposed and animated in this QuickTime movie.

As you watch the movie, follow one or two spots and observe how they move together across the Sun. Watch the movie again, and note the following characteristics of sunspots’ motion: By moving together, and moving slowly (about a month), they cannot be planets. Note how irregular they are in shape, and how they form and disappear with irregular timing. That’s not like planets either. Note the foreshortening of the spots as they approach the edge of the solar disk. That proves they’re contiguous with the surface. [2]

 

A page from Christoph Scheiner's book 'Rosa Ursina'. (Source: Univ. of Oklahoma, "History of Science.")

A page from Christoph Scheiner's book 'Rosa Ursina'.
(Source: Univ. of Oklahoma, "History of Science.")

In his famous book on optics, Rosa Ursina, Scheiner published many more detailed observations of sunspots like the one above, and no longer described sunspots as satellites. This book became a standard "textbook" on sunspots for over a century.

Sunspot drawings in Scheiner's Rosa Ursina, reproduced from

Sunspot drawings in Scheiner's Rosa Ursina, reproduced from "The history of the discovery of the solar spots," in Popular Astronomy, 24, W.M. Mitchell, 1916. This drawing illustrates the apparent paths of sunspots across the solar disk, for two sets of observations taken six months apart. Scheiner correctly concluded that the Sun's equatorial plane is inclined by 7° with respect to the ecliptic.  (Source: NASA, Technology Through Time, #31.)

1645-1710: Sunspots Vanish

As the sun entered the Maunder Minimum (1645-1710), very few sunspots were seen, and they were only sporadically reported by observer’s diligent attempts to observe them. [3]

During this period, when sunspots were observed their presence was noted as a noteworthy event by active astronomers. At that time, a systematic solar observing program was underway under the direction of Jean Dominique Cassini (1625-1712) at the newly founded Observatoire de Paris, with first Picard and later Philippe La Hire carrying out the bulk of the observations. Historical reconstructions of sunspot numbers indicate that the dearth of sunspots is real, rather than the consequence of a lack of diligent observers. A simultaneous decrease in auroral counts further suggest that solar activity was greatly reduced during this time period.

This very anachronistic plot shows the variation in observed sunspot numbers during the time period 1600-1800. The red curve is the Wolf sunspot number, and the purple line a count of sunspot groups based on a reconstruction by D.V. Hoyt. The green crosses are auroral counts, based on a reconstruction by K. Krivsky and J.P. Legrand.

This very anachronistic plot shows the variation in observed sunspot numbers during the time period 1600-1800. The red curve is the Wolf sunspot number, and the purple line a count of sunspot groups based on a reconstruction by D.V. Hoyt. The green crosses are auroral counts, based on a reconstruction by K. Krivsky and J.P. Legrand. [4]

This period is now known as the Maunder minimum, after the solar astronomer E.W. Maunder, who, following the pioneering historical investigations of Gustav Spörer (1822-1895), was most active and steadfast in investigating the dearth of sunspot sightings by astronomers active in the second half of the seventeenth century. The documented occurrence of exceptionally cold winters throughout Europe during those years may be causally related to reduced solar activity, although this remains a topic of controversy. [4]

References

  1. Technology Through Time, Issue #31: Galileo Galilei, "How could a Perfect Orb like the sun have blemishes? Some early observations of sunspots spawned two radically different opinions on this matter." NASA.
  2. Letters on Sunspots (1613) - The Works of Galileo, Sunspots and Floating Bodies, History of Science, University of Oklahoma.
  3. Technology Through Time, Issue #31: Galileo Galilei, "How could a Perfect Orb like the sun have blemishes? Some early observations of sunspots spawned two radically different opinions on this matter." NASA.
  4. 1645-1715: Sunspots Vanish - Great Moments in the History of Solar Physics, University of Montreal.

Related EoC Articles

External Links

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  •  "Rosa Ursina (1630) title page." - The Jesuit astronomer Christoph Scheiner published the definitive work of the 17th century on sunspots.  (Source: The Works of Galileo, Sunspots and Floating Bodies, History of Science, University of Oklahoma.)

Citation

Odenwald, Sten, Ph.D. (Contributing Author); Bernard Haisch (Topic Editor). 2009. "Sunspots: 17th Century." In: Encyclopedia of the Cosmos. Eds. Bernard Haisch and Joakim F. Lindblom (Redwood City, CA: Digital Universe Foundation). [First published November 26, 2007].
<http://www.cosmosportal.org/articles/view/138714/>

 

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Citation

(2009). Sunspots: 17th Century. Retrieved from http://www.cosmosportal.org/view/article/138714

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