Johannes Fabricius (1587-1615) Astronomer

Johannes Fabricius
Johannes Fabricius

Johannes Fabricius [fä-brē′tsē-s]

German astronomer who discovered the sun rotates on its axis and in 1610, while a medical student he discovered sunspots about the same time as Galileo. Noting that sunspots move, he concluded the movement was a result of rotation of the sun.

Born January 8, 1587 in Resterhafe, Netherlands in the East Friesland, and died in 1615. Johannes was the son of the noted astronomer David Fabricius (1564-1617), a Lutheran pastor and noted astronomer who discovered the variability of light in the star Mira in the Cetus constellation in 1596.

Johannes Fabricius was educated in medicine as a physician at the university in Wittenberg. In Holland, he obtained some of the earliest astronomical telescopes that were starting to circulate in the Netherlands. He first saw sunspots on February 27, 1611, (March 9 on the Gregorian calendar which had not yet been adopted in East Frisia). Shortly after his discovery he decided to team up with his father for further guidance and observation.

Johann, a studied physician, left medicine and in 1611, returned home. His father lived in Osteel, a town in the northwest part of Germany which in addition to his studies of astronomy, he was a Lutheran preacher. In Osteel, Johannes Fabricius shared his telescopes with his father, and on March 9 they collectively began to observe the sun.

At first, the Fabricius team first made their sunspot observations before and after sunrise, observing the sun directly through their telescope. According to their account:

"Having adjusted the telescope, we allowed the sun's rays to enter it, at first from the edge only, gradually approaching the center, until our eyes were accustomed to the force of the rays and we could observe the whole body of the sun. We then saw more distinctly and surely the things I have described [sunspots]. Meanwhile clouds interfered, and also the sun hastening to the meridian destroyed our hopes of longer observations; for indeed it was to be feared that an indiscreet examination of a lower sun would cause great injury to the eyes, for even the weaker rays of the setting or rising sun often inflame the eye with a strange redness, which may last for two days, not without affecting the appearance of objects."
David Fabricius
Warnfried church in Osteel, Germany where David Fabricius preached and his son Johannes Fabricius observed sun spots on March 9, 1611. Credit: NASA and Inlandsvägen

Johannes observed and made record of the black spots on the sun's surface. Sunspots had been seen by the Chinese, and Thomas Harriot observed them through telescopes in December of 1610.

To be able to observe and track sunspots without hindrance, they adopted Kepler's camera obscura technique, which allows an image of the Sun to be formed by a pinhole opening and observed, without damage to one's eyes. The Fabricius' interpretations of sunspot activity gave indication the Sun possessed an axial rotation, and in the same year Johannes Fabricius completed a short account of their observations and interpretation. It was through this publication he covered his discovery of sunspots, and the rotation of the sun on its axis.

Johannes Fabricius was the first scientist to publish a treatise on the subject. This publication lead the way to four centuries of solar research.

David Fabricius
De Maculis in Sole observatis et Apparente earum cum Sole Conversione Narratio (Narration on Spots Observed on the Sun and their Apparent Rotation with the Sun). Title page of the small pamphlet published in 1611 by Johann Goldsmid, better known by his latinized name Fabricius. He was born on 8 January 1587 at Resterhave, in East Frisia (Northwestern Germany).


  • Funk and Wagnall's Encyclopedia, ©1950
  • Encyclopedia International, ©1966 (Grolier Inc.)
  • Encyclopedia Britannica Micropedia, ©1984
  • Celebrating 400 Years of Sunspot Observations,
  • Johann Fabricius (1587-1616)
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