is required to explain this). At any rate, the effect would have been too small for cannoneers of the time to detect. The star size argument Riccioli also used telescopic observations of stars to argue against the Copernican theory. Viewed through the small telescopes of his time, stars appeared as small but distinct disks. These disks were spurious – caused by the diffraction of waves of light entering the telescope. Today they are known as Airy disks, after the nineteenth-century astronomer George Biddell Airy (1801–1892). The real disks of stars are generally too tiny to be seen even with the best of modern telescopes. But during most of the seventeenth century it was thought that these disks seen in a telescope were the actual bodies of stars. In the Copernican theory, the stars had to lie at vast distances from Earth in order to explain why no annual parallax was seen among them. Riccioli and Grimaldi made numerous measurements of star disks using a telescope, providing a detailed description of their procedure so that anyone who wanted could replicate it. Riccioli then calculated the physical sizes that the measured stars would need to have in order for them both to be as far away as was required in the Copernican theory to show no parallax, and to have the sizes seen with the telescope. The result in all cases was that the stars were huge – dwarfing the sun. In some scenarios one single star would exceed the size of the entire universe as estimated by a geocentrist like Tycho Brahe. This problem that the appearance of stars in the telescope posed for the Copernican theory had been noted as early as 1614 by Simon Marius, who said telescopic observations of the disks of stars supported the Tychonic theory. The problem was acknowledged by Copernicans such as Martin van den Hove (1605–1639), who also measured the disks of stars and acknowledged that the issue of vast star sizes might lead people to reject the Copernican theory. Other arguments The other arguments Riccioli presents in Book 9 of the New Almagest were diverse. There were arguments concerning: whether buildings could stand or birds could fly if Earth rotated; what sorts of motions were natural to heavy objects; what constitutes the more simple and elegant celestial arrangement; whether the heavens or the Earth was the more suited for motion and the more