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Background
Jean Tarde (born in 1561 in La Roque-Gageac near Sarlat, France, died in 1636 in Sarlat, France) was an early French Copernican and a student whose primary study was on sunspots. Tarde was born into a family whose social status isn’t completely known, but it is speculated that they were bourgeois. This speculation comes from when he died, he left behind a large estate, and his family remained in a high status within the bourgeois community.

Education and Religion
Jean Tarde received his doctorate in law from the University of Cahors and then continued his studies at the University of Paris where he became an expert in mathematical sciences.

After finishing school, he was ordained a priest and was then assigned to the parish of Carves near Belvès. After spending some time there, he was promoted to canon theologian of Sarlat’s cathedral. He was appointed as vicar general in 1594 by the bishop of Sarlat at the time, Louis de Salignac. A few years after this, Henri IV appointed Tarde as an almoner, for which he received a pension.

Cartography
In 1594 when Tarde was appointed as vicar general, Louis de Salignac wanted to learn more about the effects of France’s religious wars on the Dioces, so he commissioned Tarde to map out the diocese due to his cartography skills.

In 1606, he mapped out the neighboring diocese at the request of bishop of Cahors in 1606. With this task, Tarde put together a quadrant that was fitted with a compass needle and attached this device to a sundial. This device interested the Bishop greatly, where he encouraged Tarde to write his book Les usages du quadrant à l’esguille aymantée (1621), which was dedicated to the Bishop. Tarde cartographic work established his curiosity in geometry, drawing, drafting, and the uses of technical instruments which would prove extremely useful in his work in astronomy.

Study on Sun Spots
The controversy of sun spots was one of the most acrimonious quarrels of the early Scientific Revolution between astronomers starting in the late 1500s. Jean Tarde was at the forefront of these disputes where the main aspects regarding sunspots included whether the visual data of sunspots seen through telescopes were valid perceptions, if the discovery of the suns spots and their further inspection were even a priority, and what the nature of the spots were, provided the visual perceptions of them were real and valid. The third aspect of these disputes became one of the most important, because if these observations were to be accepted, it would heavily challenge the fundamental principles of cosmology where the sun was considered flawless.

Tarde’s study on sun spots primarily began in 1614 where he took a trip with his bishop to Italy. During this trip, Tarde was able to visit Galileo in Florence to further discuss his findings and learn of Galileo’s related discoveries. Tarde flattered Galileo when first seeing him by telling him that he read his book. He told Galileo about his sighting of two stars around Saturn, the phases of Venus, and the spots on the face of the sun. It was mentioned that many other astronomers in Rome had also seen these spots, some even with the naked eye, and that this was not a trick perceived through telescopic lenses. In response, Galileo informed Tarde that the spots were not still, that they followed a certain path along the middle of the Sun, and that the time for them to across was approximately fourteen days. Galileo concluded to Tarde that these spots were not close to the Earth, but instead were very close to the Sun, if not on the Sun itself. At the end of his visit with Galileo, Tarde questioned how a telescope works, where Galileo’s response was to direct him to Kepler’s Book on Optics along with giving him his book on sunspots. Galileo also promised to send Tarde one of his best lenses to aid him in his research while in Rome. It is unclear, though most unlikely, that Galileo ever sent it to him.

In 1615, Tarde returned to his observatory in Sarlat and continued to observe the Sun. He would further observe the spots and record his observations until 1620 when he would publish his book on the subject, titled Astres de Borbon. In his book, Tarde reveals his hypothesis on the spots and speculates that they are bodies that orbit around the Sun. He named these bodies the “Bourbon Stars” in dedication to king Louis XIII as an attempt to flatter the ruling dynasty and gain more funding for his work, though he did not receive it. His conclusion came primarily from his belief that the sun was perfect with no blemishes and his favoritism toward heliocentric theory.

Tarde’s theories on sun spots sparked a debate between him and Galileo, where Galileo questioned some of Tarde’s claims on planetary theory. As Galileo believed the spots to be on the Sun itself due to the absence of parallax, Tarde also agreed that the parallax was difficult to detect but that this could be reasoned by the blurring of vision caused by the sun’s brightness. Many of Tarde’s arguments against Galileo held up, but he did have to rely many times on his observation that the sun had a blurring effect on the vision due to its brightness in many of his rebuttals.