The Intellectual Battle Over the Nature of Sunspots! ❤️

On Sunspots and their Intriguing Lore

25th December 2025

#intothewildwithrufus | Physics of Cool Darkness | Telescopic Astronomy | Freckles in the Sun | Engine of our Solar System

After an exciting morning of trekking and birding in the wild, in the distant banks of the River Cauvery, we came back to camp, exhausted albeit deeply satisfied! Then, flipping through the morning’s lovely snapshots, I shared the picture of the early morning sun in all its sublime grandeur, with my wife.

She was all in awe, and exclaimed, ‘I’m teaching sunspots in the sun to my students right now. This is so amazing!’

Well, this piqued my curiosity still further, and I wanted to explore! 😊

According to NASA,

Sunspots are dark spots that freckle the face of the Sun. These sunspots are in fact, cooler regions on the Sun caused by a concentration of magnetic field lines.

Sunspots are the visible component of active regions, areas of intense and complex magnetic fields on the Sun that are the source of solar eruptions.

Sunspots can be seen on the Sun’s photosphere, or visible surface of the Sun. The number of sunspots goes up and down as the Sun goes through its natural 11-year cycle. Scientists use sunspots to help them track this cycle,

says NASA’s feature article in their official website.

Added, I stumbled upon a lovely book titled, On Sunspots: Galileo Galilei & Christoph Scheiner, translated & introduced by Eileen Reeves & Albert Van Helden, that proved a vital read on the topic of sunspots in the sun!  

[Surprisingly Reeves is a Professor of Comparative Literature while Helden is a Professor of the History of Science! What a lovely combo to come up with such a spirited book on sunspots!]

Well, this book is a historical and scientific compilation that documents one of the most significant astronomical debates of the 17th century.

The book details on the intellectual battle over the nature of sunspots and, by extension, the perfection of the heavens.

And the central conflict to the battle was whether sunspots were actually on the surface of the Sun or were small planets/stars orbiting it. Scheiner initially argued they were “wandering stars” to preserve the Aristotelian idea that the heavens (and the Sun) were perfect and unchanging.

However, Galileo argued that sunspots were contiguous to the Sun’s surface, appearing and disappearing like clouds. He used mathematical demonstrations to show that their changing shapes and speeds as they moved across the solar disk proved they were on or very near the Sun’s rotating body.

Through his study of these spots, Galileo concluded that the Sun itself rotates on its axis, carrying the spots with it—a revolutionary idea at the time.

And here goes some lovely vignettes from the book for us all –

Sunspots have been observed for thousands of years, with systematic telescopic records beginning in 1610 (by Galileo, Harriot, and others).

Unlike studying a distant galaxy, sunspot data has immediate consequences for Earth.

By monitoring sunspot size and magnetic complexity, scientists can predict geomagnetic storms that could knock out power grids, disrupt GPS, or damage satellites. Sunspots are a masterclass in thermal and magnetic physics.

The study of sunspots emerged in the second decade of the seventeenth century as an essential element of the debate about the nature of the heavens.

The instrument that made these and other celestial features visible, the telescope, was still a novelty, and the observations made with it were likewise subjects of controversy and negotiation.

Telescopic astronomy, as we might call it, was a subject that could not have been imagined in 1607 - the year before the instrument came into use - and in 1612 and 1613, when the sunspot controversy raged.

In the Western tradition, the scientific study of sunspots dates from the early seventeenth century, when the telescope made them apparent to observers.

Though for the most part so small that they remain undetected in the bright field of the Sun, from time to time larger spots have been visible to the naked eye. Because of their interest in celestial omens, Far Eastern observers carefully noted such spots, and records dating back to at least 165 BC have come down to us.

The earliest known Western reference, attributed to Theophrastus of Eresus in the fourth century BC, merely states that “black spots in the Sun and the Moon foretell rain, and reddish ones wind.” 

Virgil’s more ample presentation of sunspots appeared in the first book of the Georgics, composed around 36–29 BC.

It is significant in that it describes such spots, portrayed as maculae or “flecks,” as the best indices of approaching storms or showers, and treats phenomena that medieval and early modern observers would find rare and astonishing as quotidian, fleeting, and natural.

Much attention has been devoted to the question of priority in telescopic sunspot observations, the principal candidates being Thomas Harriot, Johannes and David Fabricius, Galileo Galilei, and Christoph Scheiner.

The origins of these controversies must be found in the writings of Galileo and Scheiner themselves, and for the most part learned men of the early modern period believed Galileo’s account.

The book thus serves as a “history of the controversy,” to show how the debate evolved between these two scientific giants.

In short, while most astronomical research focuses on distant, static, or ancient events, sunspot observation is a daily “real-time” pulse check on the engine of our solar system.