Riccioli On Mizar

This is the facsimile of the famous and frequently quoted note about Mizar's being a double star.

Giovanni Battista Riccioli: Almagestum Novum, Tom. I., Part I. (Liber Sextus: De Stellis Fixis), p. 422 (Bononiae: Ex typographia haeredis Victorij Benatij, 1651). National Library, Prague.

Translated from Latin by Thomas Winter, the associate professor of classics at the University of Nebraska, it reads as follows:

"Chapter IX – On apparent and real dimensions of stars


The first way to observe the diameters of stars depends on ocular estimate, and on comparison either with the diameter of the moon, or – so its brightness won't be a problem – with the known distance of fixed stars close together to each other, the pure distance of the Pleiades, the Hyades, or the Goats to each other, by estimating how many such stars would be needed to fill that interval. This conjecture is, of course, liable to error, especially on account of artificial rays enlarging the stars and shrinking the intervals, the way that there appears to be one star in the middle of the Great Bear's tail, when there are actually two, as the telescope reveals. On this account, Galileo (Dialogo dei Massimi Sistemi del Mundo, volume terzo) thinks it better that diameters be observed in a luminous ambience, near the sun or moon, because then they are stripped of those spurious rays, just as it appears when Venus is seen by day, and in lamp flames seen by day at some distance, and I have frequently experienced in full moons."