The question of who first observed sunspots is complex, as the early 17th century saw multiple independent observations. Sunspots are temporary, visible features on the Sun’s surface, and their study became intertwined with the greatest scientific debates of the time. The historical context of their first telescopic observation involves a controversy between several European astronomers who pointed their new instruments at the Sun almost simultaneously.
Defining Sunspots
Sunspots are regions on the Sun’s photosphere that appear darkened because their temperature is lower than the surrounding material. This temperature drop, typically from about 10,000 degrees Fahrenheit in the photosphere to around 6,500 degrees Fahrenheit in the spot itself, is caused by intense concentrations of magnetic flux emerging from the Sun’s interior. These powerful magnetic fields inhibit the convection of hot gas from below, effectively cooling the surface area they cover.
A sunspot typically consists of a dark central area called the umbra, surrounded by a lighter region known as the penumbra. Sunspots can be many times the size of Earth. The number of sunspots visible changes in a regular pattern known as the solar cycle, which averages about 11 years in length. This cycle represents a fundamental variation in the Sun’s magnetic activity, influencing phenomena like solar flares and coronal mass ejections.
Early Observations and Pre-Telescopic Records
Before the invention of the telescope, sunspots were occasionally visible to the naked eye when the Sun’s brightness was naturally dimmed by atmospheric haze, fog, or when viewed near sunrise or sunset. For millennia, cultures around the world documented these transient dark patches. The earliest known records come from ancient Chinese astronomers, with observations possibly dating back to the 12th century B.C.
Systematic records from China began around 28 B.C., noting “a black vapor as large as a coin” at the center of the Sun. In the West, the Greek philosopher Theophrastus mentioned a sunspot around 300 B.C. However, these early European sightings were often dismissed or misinterpreted, such as a large spot seen in A.D. 807 being mistaken for a transit of Mercury. This reluctance stemmed from the prevailing philosophical view that the heavens were perfect and unblemished.
The Simultaneous European Discoveries (1610-1611)
The advent of the telescope in the early 17th century transformed the observation of sunspots from rare glimpses into systematic study, sparking the controversy over who deserves credit for the discovery. Four individuals—Thomas Harriot, Johannes Fabricius, Christoph Scheiner, and Galileo Galilei—independently turned their new instruments toward the Sun between late 1610 and early 1611.
The English astronomer Thomas Harriot made the earliest known telescopic observations and drawings, beginning on December 8, 1610. Harriot, however, never published his notes, which remained largely unknown until the late 18th century. The German astronomer Johannes Fabricius and his father David observed sunspots in March 1611 and were the first to publish their findings, releasing the pamphlet De Maculis in Sole Observatis in June 1611. This publication correctly identified the spots as features on the Sun itself, deducing the Sun’s rotation from their movement.
The Jesuit mathematician Christoph Scheiner began his observations in March or April 1611 and published his first account in January 1612 under the pseudonym “Apelles.” Scheiner initially argued that the spots were small, dark planets orbiting the Sun, a position meant to preserve the Aristotelian idea of a perfect, immutable Sun. Galileo Galilei began his systematic observations around the same time, demonstrating the spots to audiences in Rome in the spring of 1611. Galileo published his definitive work, Letters on Sunspots, in 1613, which used meticulous observations to refute Scheiner’s planetary hypothesis and provide evidence that the spots were features on the solar surface.
The Cosmological Impact of the Discovery
The telescopic observation and confirmation of sunspots had profound implications that extended beyond astronomical curiosity. This discovery directly challenged the long-standing Aristotelian model of the cosmos, which held that celestial bodies were made of an unchangeable, perfect substance. The transient, changing nature of the sunspots provided undeniable visual evidence that the Sun was not a flawless sphere but was subject to generation and decay, just like Earth.
The consistent movement of the spots across the Sun’s face, disappearing on one side and reappearing on the other, demonstrated that the Sun was rotating on its own axis. This observed rotation provided support for the emerging heliocentric model, which required the Sun to be a dynamic, rotating body. The sunspots were physical proof that the old cosmology was fundamentally incorrect, ushering in a new understanding of the universe.