Before the invention of telescopes, it seemed to contradict Copernicus’s opinion, to make the sun one of the fixed stars. For the stars of the first magnitude being esteemed to be about three minutes diameter; and Copernicus (observing that though the earth changed its place, they always kept the same distance from us) having ventured to say that the magnus orbis [Earth’s orbit] was but a point in respect of the sphere in which they were placed, it was a plain consequence that every one of them that appeared any thing bright, must be larger than the path or orbit of the earth: which is very absurd. This is the principal argument that Tycho Brahe set up against Copernicus. But when the telescopes took away those rays of the stars which appear when we look upon them with our naked eye, (which they do best when the eye-glass is blacked with smoke) they seemed just like little shining points, and then that difficulty vanished, and the stars may be so many suns.
Christiaan Huygens (1629-95)
The Celestial Worlds Discover’d (London, 1722)
Page 145
That is how the astronomer Christiaan Huygens outlined Tycho Brahe’s “principal argument” against the heliocentric world system of Copernicus. Brahe’s argument was important. Brahe was the most prominent astronomer of his age. This argument that he set up against Copernicus would be cited by all sorts of opponents of Copernicus, including Simon Marius (who named the moons of Jupiter), and the Jesuit astronomers Giovanni Battista Riccioli, Christoph Scheiner, and Andreas Tacquet (and, by the way, Huygens was wrong in that Marius and Riccioli specifically used the argument with the telescope). Melchior Inchofer, S.J., who was appointed by Pope Urban VIII to criticize Galileo’s Dialogue Concerning the Two Chief World Systems, cited the argument. But where did Brahe (1546-1601) get this star size argument?
I think he got it from a thousand-year-old discussion regarding the sizes of celestial bodies and the first chapter of Genesis. I think he got it from Augustine of Hippo (354-430). I have talked here at Sacred Space Astronomy about the star size argument, and about the connection of Augustine, Genesis 1:14-16, and the sizes of the stars to that argument. But I believe I have now managed to find evidence connecting Brahe and Augustine.
The connection is found in an exchange of letters in 1588-89 between Brahe and the astronomer Christoph Rothmann (d. ~1600). Rothmann had brought up the question of Genesis and the sizes of stars in a letter of 19 September 1588, in which he was advocating for a free interpretation of the Bible on matters of astronomy:
The scriptures are not written only for you and me, but for all humanity altogether; indeed, they speak to the comprehension of all, as indeed all theologians acknowledge in explications of Genesis Chapter 1. Otherwise the moon might be greater than the rest of the stars, contrary to geometrical demonstrations. But from those, that is clear.
Rothmann had also brought up Augustine, at the start of a letter of 22 August 1589 which he opened by defending himself from what he saw as Brahe’s accusation that he was being too free with the words of scripture. “If you will read Augustine,” Rothmann told Brahe, “you will discover much freer speaking concerning the sacred writings.”
One instance in which Brahe had suggested that Rothmann was being too free with scripture was in a 21 February 1589 letter, where Brahe had discussed Genesis 1 and the matter of the “two great lights” of Genesis 1:14-16. Here Brahe had mentioned that “Moses” (Genesis) called the sun and moon “great” based on “magnitude of light”, not on “size of bodies”. Brahe had also mentioned the vast distances of the stars, and he had noted Moses’s need to not delve into the details of astronomy, “for he is writing to a rude people” — thus agreeing with what Rothmann had written the previous September. But Brahe told Rothmann, “You disparage the Prophets too much, when you assert that they do not understand more than the common people concerning the nature of things.”
Brahe responded to Rothmann’s August letter in a letter of 24 November. He starts the letter by assuring Rothmann that he was never questioning his piety, and also by again drawing attention to Moses and the magnitudes of the moon and stars. Brahe then touches on Augustine. Quite a bit later in this lengthy letter, Brahe again brings up Moses and the two great lights — and in the same (lengthy) sentence he mentions Augustine. However, the mention is regarding theologians and the motion of the Earth, and not about those lights.
Two pages later, in the same letter, Brahe lays out his “principle argument”. The fact that observations of the same stars from different locations on Earth’s orbit are not found to differ, he says, puts a minimum distance on the stars — seven hundred times the distance to Saturn. Given that,
Then stars of the third magnitude which are one minute in [apparent] diameter will necessarily be equal to the entire annual orb [Earth’s orbit], that is, they would comprise in their diameter 2,284 semidiameters of the earth. They will be distant by about 7,850,000 of the same semidiameters. What will we say of the stars of first magnitude, of which some reach two, some almost three minutes of visible diameter? and what if, in addition, the eighth sphere were removed higher [that is, if observations were improved and yet did not yield a detection of differences between different locations on Earth’s orbit, so that the minimum distance to the stars must become greater], so that the annual motion of the earth vanished entirely [and was no longer perceptible] from there? Deduce these things geometrically if you like, and you will see how many absurdities (not to mention others) accompany this assumption [of the motion of the Earth] by inference.
There is the principal argument. Now, nowhere does Brahe directly indicate that this argument derives from Augustine. It could just be a matter of coincidence that he had discussed both Augustine and (separately) the two great lights question in the same letter to Rothmann in which he put forth his principal argument. But I think the case for coincidence seems weaker than the case for the principal argument being derived from Augustine and the matter of the “two great lights”.
If you are interested in a full scholarly treatment of this matter, including discussion of how the telescope came to bear on it, see “Whence Tycho’s Case against Copernicus? On Genesis, Augustine, and the Stars” (arXiv:2312.09898). ArXiv material is open access — just CLICK HERE and then select the option to download the PDF.
