The portrait of Kepler you have seen is not actually Kepler

The widely circulated portrait of Kepler is not of Kepler? Then who is he?

Written by Ye Lingyuan

Like all disciplines, the history of physics is written by physicists. In order to present this history more vividly, we can usually see many portraits or photos of physicists in physics textbooks or popular science articles: Leibniz and Newton with thick curly hair; playful Einstein with his tongue sticking out in front of the camera and his hair flying; Marie Curie, who is serious in black in the laboratory; and the group photo of the Solvay Conference, which is "worshipped" by many students studying physics, etc. These portraits and photos do bring us closer to the history of physics development, and find a more human side behind the increasingly abstract ideas of physics; they also allow us to glimpse the different personalities of physicists.

However, not all portraits in these documents are accurate. In popular science articles and other Internet resources in the past decade or so, the portrait of Kepler, a medieval physicist who made fundamental contributions to modern physics and astronomy, seems to contain serious misuse.

Kepler lived after Galileo and before Newton, and was a famous astrologer at the time. His most famous contribution to physics was that he used the massive astronomical data that Tycho had painstakingly collected for many years to summarize and discover the three laws of motion of the planets in the solar system, which directly promoted Newton's discovery of the law of universal gravitation. Kepler believed that the universe was geometric. In his early days, he used the nesting of six Platonic cubes to construct a cosmic model, which corresponded to the six known solar system planets at the time; he also believed that the universe was musical, and the harmony of the universe could be explained by music. The movement of the entire universe was composing a beautiful piece of music. How romantic!

If you open Baidu and search for Kepler, the first portrait that appears under the Kepler entry in Baidu Encyclopedia as of the time I finished writing this article is shown below on the left; the picture on the right also appears in the album under the Kepler entry.

Previously, there were two portraits of Kepler in Baidu Encyclopedia.

The portrait on the left is also the main image under the Kepler entry on Wikipedia. If you search online for popular science articles about Kepler, they will most likely choose this picture as Kepler's portrait and display it in the text. For example, the popular science article titled "Why Kepler is called the 'Lawmaker of the Sky'" on Science Popularization China includes this portrait [1]. Many more professional organizations have also used this picture: NASA used this picture in its 2017 teaching materials on exploring the solar system; the European Space Agency also cited this portrait on Wikipedia in an earlier press release. If you have time, you can find more examples.

Based on the two images provided by Baidu Encyclopedia, it is hard to believe that the two different portraits above depict the same person: the portrait on the left clearly has more prominent cheekbones and a wider nose bridge; the facial proportions of the portrait on the right are obviously different, with the ratio above and below the eyebrows being almost 1:1. The Kepler image used in the Kepler entry under the astronomy category of the Encyclopedia of China database is more consistent with the portrait on the right above [2].

In fact, the portrait on the left is most likely a fake. The original is now kept in a Benedictine monastery in Kremsmünster, Austria. The canvas is made of oak and has no signature or mark anywhere on the painting; these marks are often omitted in copies. Only in the upper right corner of the painting is there a Latin inscription "Aetatis Suae 39, 1610" (Thirty-nine years, 1610), indicating the date of the painting and Kepler's age at the time. But anyone who knew Kepler's birthday could have added it to the painting.

In an article published in 1930 to commemorate the 300th anniversary of Kepler's death, astronomer Ernst Zinner recorded the opinion of Seraphin Maurer, director of the Vienna Academy of Fine Arts, on this portrait[3]. Maurer had examined the painting in the 1920s. He believed that although the painting as a whole was consistent with paintings from the 17th century, the techniques and brushstrokes of the painting showed that the painter was only mechanically imitating the works of others without any understanding of the natural form of things. At the same time, if the painting was really completed in 1610, its pigments should show signs of aging such as cracking like paintings of the same period, but this painting did not show obvious similar signs. All these signs led Maurer to speculate that the painting was just a copy and that it was actually painted around 1800.

As Zinner said in the same article, the person in this fake painting is not even Kepler. It is most likely a copy of the portrait on the left below. There is a clear signature and attribution on the upper right side of this portrait. It is a portrait of Kepler's teacher Michael Mästlin. If you compare this portrait with the portrait in the encyclopedia shown above on the left, you can find that the two portraits are very similar, from the objects in the hands to the style of clothing to the details of the face.

Left: Kepler's teacher Michael Mästlin; Right: Kepler

Kepler's official portrait is shown above on the right, with detailed information also marked in the upper left corner. By comparison, we can see that this portrait is more consistent with the second picture under the previous Baidu Encyclopedia entry. Their facial features are more consistent: the official portrait also shows that Kepler has a very broad forehead, which may be a symbol of wisdom.

The most obvious difference between the two sets of images is the clothing. Both the figure in Mästlin's and the supposedly fake Kepler portraits are wearing academic robes with pleated collars, which were commonly worn by professors at the time. This style of collar is called a ruff collar and was a typical feature of aristocratic clothing from the mid-16th to the mid-17th century. However, judging by Kepler's official portraits and the oval medallion from his wedding in 1597, Kepler is more likely to be wearing a lace collar: this may be more consistent with his status, as he was neither a scholar nor a noble at the time.

Portrait of Kepler and his wife Barbara Müller

How this portrait of Kepler, which is most likely a forgery, has been so widely circulated in the past decade is unknown. But since it is still the main photo under Kepler's entries on Baidu Baike and Wikipedia, this error may spread further. Although this will not lead to the erasure of Kepler's contributions to physics and astronomy, if the wrong portrait occupies our mind's impression of Kepler, it does not show the respect we should have for him. This year is the 450th anniversary of Kepler's birth, and it is time to put an end to this misinformation that may have been spread unintentionally.

(Postscript: It is worth mentioning that before this article was officially published, Baidu Encyclopedia had deleted the suspected fake Kepler portrait from the Kepler entry, which is certainly a good start. I hope that from now on, articles about Kepler will allow us to see Kepler's correct face.)

Notes

[1] Why is Kepler called the “Lawmaker of the Sky”? 2017, Science Popularization China, http://www.xinhuanet.com//science/2017-03/01/c_136088669.htm

[2] https://h.bkzx.cn/item/86649?q=Kepler

[3] E. Zinner, Ber. Naturwiss. Ver. Regensbg. 19, 337 (1928/1930), pp. 339.