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It is time for a second post about research! (I had another one some weeks ago.) Research goes on at the Vatican Observatory, and yours truly here contributes to the research output of the VO. Here I again share some of the nuts and bolts of that research with Sacred Space Astronomy readers, and especially with subscribers, as those readers who are also subscribers actually help fund the operation of the Vatican Advanced Technology Telescope, or VATT, on Mt. Graham in Arizona, and its associated programs.
I am working on a paper about Jacques Cassini, a French astronomer from the 18th century. (My main area of research is the history of astronomy, and that has been my main area for roughly 15 years now.) Jacques Cassini was the son of Giovanni Domenico Cassini, the man for whom both NASA’s Cassini probe to Saturn and the Cassini Division in Saturn’s rings system are named. Jacques was born at the Paris observatory where his father worked.
In the early 18th century Jacques attempted to determine the distance to, and size of, the star Sirius. There were problems with both his distance measurement and his size measurement, but those problems were not obvious at the time. Cassini’s measurements indicated Sirius to be very far away, and very, very large—so large that, were it placed within the solar system, it would extend from the sun to the orbit of Earth. Indeed, Cassini said that Sirius compared to the sun was like the sun compared to the Earth; a million Earths would fit within the sun, and a million suns would fit within Sirius. Moreover, while Cassini did not mention this explicitly, his measurements also indicated that Sirius was very dim compared to the sun.
Then Jacques Cassini proceeded to suppose that all stars were like Sirius. Of all stars in the night sky, Sirius appears the brightest, so the reason the other stars appear to differ from Sirius in brightness would then be because they are more distant than Sirius in varying degrees. So Cassini was arguing for a universe in which the stars were, in essence, not like the sun, but instead were bodies a million times the volume of the sun (and, necessarily, far more dim than the sun).
This is the same sort of starry universe that Johannes Kepler had argued for a century earlier. It was the sort of universe that careful astronomers had to accept, at least if they both accepted the measurements of the stars and the theory of Nicolaus Copernicus that said that the Earth orbited the sun. Yet what is particularly interesting about this story is that Cassini’s fellow astronomers paid no attention to his ideas about the nature of the starry universe, even as they paid attention to and valued his data on Sirius. Typically, they misread what Cassini said, so as to make all stars like Sirius, and to make Sirius like the sun. Thus every star would be a sun—which is of course contrary to what Jacques Cassini said.
As I mentioned, there were flaws in Cassini’s measurements, but those flaws were not so obvious at the time. Thus, like Kepler, Cassini produced a scientifically strong case for a Copernican universe in which the stars were not other suns. Yet astronomers read Cassini’s work and continued to speak of the stars as being suns.
Of course, Jacques Cassini and Johannes Kepler were wrong about the nature of stars. Today we know that there is great diversity in stars: a very few are as large as Cassini calculated (indeed, some are a good deal larger), and those are very bright; more stars are actually comparable to the sun; and many more still are very dim “red dwarf” stars that are far outclassed by the sun. Indeed, we should say that the sun is a star, rather than that stars are suns, as we would say that a beagle is a dog, rather than that dogs are beagles (there being great diversity in dogs, as there is great diversity in stars). Nonetheless, we do commonly refer to stars as being “other suns”.
However, Cassini’s story suggests that it is likely that astronomers viewing the stars as being other suns predated any scientific evidence for such a view. His story shows that there was a strong scientific reason to believe that stars were not other suns, but were the giant dim bodies that Kepler said they were—and yet astronomers latched on to the idea that stars were suns anyway.
I have completed a working draft of this paper and submitted it to a journal. The draft has made it past the editor, and is now out for peer review. But those who are gung-ho enough to be interested in this research can read the working draft by clicking on the link below... but only if you are a paid-up member of Sacred Space, and logged in as such (if you are not, the link will not be visible). The paper is 26 pages with 3 figures, so it will keep you entertained for a while. Enjoy a look at the very cutting edge of knowledge! 🙂