On the Method of Observing the Changes That Happen to the Fixed Stars; With Some Remarks on the Stability of the Light of Our Sun. To Which is Added, a Catalogue of Comparative Brightness, for Ascertaining the Permanency of the Lustre of Stars. By William Herschel, LL. D. F. R. S
Philosophical Transactions of the Royal Society of London
c 166 3 IX. On the Method of observing the Changes that happen to the fixed Stars ; with some Remarks on the Stability of the Light of our Sun. To which is a d d e d , a Catalogue o Brightness, for ascertaining the Permanency of the Lustre of Stars. By William Herschel, LL. D. F .R .S. v Read February 25, 1796. T he earliest observers of the stars have taken notice of their different degrees of brilliancy, and, by way of expressing their ideas to others, have classed them into magnitudes.
... o magnitudes. Bright ness and size among the stars were taken as synonymous terms, and may still be used as such with sufficient truth, notwithstanding the latter, it seems, can only be looked upon as the consequence of the former. The brightest stars were called of the first magnitude; the next of the second; and those of an inferior lustre of the third, fourth, and fifth mag nitudes ; and so on. Among the stars of the first two or three classes there seems to be some natural limit which confines them to a par ticular order. If we suppose the stars to be about the size of our sun, and at nearly an equal distance from us and from each other, those which form the first inclosure about us will appear brighter than the rest, and there can be only a small number of them. This hypothesis is nearly confirmed by observation, as may be seen by looking over a globe, and applying a pair of compasses opened to 60 degrees, which * I use the letter m in a short way to express the magnitude o f the stars.