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Updated: June 6, 2025
But now comes the camera, a veritable new eye for science, as sensitive as the optic nerve and a thousand times more steadfast and tireless, being able to hold its gaze upon the minutest object of search hour after hour, without blinking. It is with this new eye that Dr. Pritchard has succeeded, as he thinks, in reading the infinitesimal figures on the milestone of the star 61 Cygni.
The light year is taken as the unit of measurement in the starry heavens, as the earth's mean distance is "the astronomical unit" for the solar system. The proper motions and parallaxes combined tell us the velocity of the motion of these stars across the line of sight: alpha Centauri 14.4 miles a second=4.2 astronomical units a year; 61 Cygni 37.9 miles a second=11.2 astronomical units a year.
Its magnitudes are six and seven, distance 0.66", p. 74°. The next step carries us to a very famous object, 61 Cygni, long known as the nearest star in the northern hemisphere of the heavens.
As an educative object for those unaccustomed to celestial observations it may be compared among star clusters to beta Cygni among double stars, for the most indifferent spectator is struck with wonder in viewing it.
With its companion, it revolves round their common centre of gravity in eighty-one years, and hence it would seem that their conjoint mass is less than that of the sun. The star 61 Cygni is of the sixth magnitude. Its parallax was first found by Bessel in 1838, and is about one-third of a second. The distance from us is, therefore, much more than five hundred thousand times that of the sun.
See gathered a rich harvest of nearly 500 new southern pairs with the Lowell 24-inch refractor in 1897. Professor Hough's discoveries in more northerly zones amount to 623; Hussey's at Lick to 350; and Aitken's already to over 300. There is as yet no certainty that the stars of 61 Cygni form a true binary combination. Mr.
On this ground alone, 61 Cygni was admitted to be a genuine double star; and it was shown that, although its components appeared to follow almost strictly rectilinear paths, yet the probability of their forming a connected pair is actually greater than that of the sun rising to-morrow morning.
But a sensible parallax of about one second has been ascertained in the case of the double star, alpha alpha, of the constellation of the Centaur, and one of the third of that amount for the double star, 61 Cygni; which gave reason to presume that the distance of the former might be about twenty thousand millions of miles, and the latter of much greater amount.
When at last, January 9, 1839, Henderson communicated his discovery to the Astronomical Society, he could no longer claim the priority which was his due. Bessel had anticipated him with the parallax of 61 Cygni by just two months. Thus from three different quarters, three successful and almost simultaneous assaults were delivered upon a long-beleaguered citadel of celestial secrets.
H. Corder, on whose notification Mr. Espin, on August 21, examined its nearly monochromatic spectrum. The metamorphosis of Nova Cygni seemed repeated. The light of the new object, like that of its predecessor, was mainly concentrated in a vivid green band, identified with the chief nebular line by Copeland, Von Gothard, and Campbell. The second nebular line was also represented.
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