The Medieval Friar Who Foretold Carl Sagan’s “Star-Stuff”

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WWe are made of star stuff. Few scientific ideas have had as much cultural resistance as this one, which Carl Sagan popularized in his 1980 television series. Cosmos. The phrase has become almost secular scripture, cited in hundreds, if not thousands, of books, splashed on T-shirts and tote bags, tattooed on skin, and repeated at weddings.

Sagan intended the phrase to be understood in a very literal sense. According to modern astrophysicists, the nitrogen in our DNA, the calcium in our teeth, and the iron in our blood were all forged inside collapsing stars and then circulated throughout the universe. “The cosmos is within us,” Sagan said. “We’re made of star stuff.”

Some 800 years earlier, a Dominican friar had a similar idea. In the 1240s, theologian and philosopher Richard Fishacre drew on his understanding of color and light to argue that the stars and planets were made of the same elements we find here on Earth. His idea linking terrestrial matter to celestial bodies challenged the Aristotelian worldview dominant at the time. Aristotle had proposed that the heavens and all the moons and planets within them were made up of a perfect, transparent and immutable fifth element, totally distinct from the four parts of our planet: water, fire, air and earth. Fishacre was one of the first people to challenge this model, thereby bridging the metaphysical divide between Heaven and Earth.

Read more: »When we were the cosmos»

Fishacre arrived at his reasoning by observing the interaction of color and light in stars and planets, writes William Crozier in The conversation and in an article on Fishacre in the Theological Review New Blackfriars.

Without the aid of a telescope, Fishacre noticed, for example, that Mars emitted a faint red light and Venus a yellowish glow. Color, he noted, is associated with opaque substances, which are always made of one or more of the four earth elements. But the observation that he believed most favored his new concept was that the Moon could obscure the Sun during an eclipse, which would not be possible if it were transparent like glass. The nature of the eclipse suggested that the Moon was also made of physical substance and obeyed natural laws similar to those of Earth. If this was true of the Moon, he reasoned, it must also be true of the rest of the elements in the cosmos.

Fishacre, who was the first Dominican friar to teach theology at Oxford University, was criticized at the time for his ideas, but modern astrophysics continues to vindicate him today, Crozier writes. Not long ago, scientists used the James Webb Space Telescope to determine that the atmosphere of a Neptune-like exoplanet, known as TOI-421 b, located 244 million light-years from Earth, is rich in water and sulfur dioxide, elements common on our home planet. The researchers were able to confirm this chemical composition using a process closely related to the humble observations Fischacre relied on: transmission spectroscopy, which detected subtle variations in color and light emitted by the exoplanet that could only be explained by the presence of water and sulfur dioxide.

Of course, Fishacre’s ideas were philosophical and observational rather than quantitative or chemical. And there is no evidence that Sagan or any other modern astronomer relied directly on his arguments to formulate theirs. But the thematic echoes suggest a much earlier evolution of the idea that we are cosmic.

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Main image: Bruce Rolff / Shutterstock

• Kristen French

  Published on November 17, 2025

  Kristen French is an associate editor at Nautilus. She has worked in science journalism since 2013, reporting and writing articles and news for publications such as Wired, Backchannel, The Verge, And New York Review. She holds a master’s degree in science journalism from Columbia University.