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Updated: May 5, 2025
On September 5, 1877, Mars came into opposition near the part of his orbit which lies nearest to that of the earth, and Dr. He chose, as the scene of his labours, the Island of Ascension, and for their plan a method recommended by Airy in 1857, but never before fairly tried. This is known as the "diurnal method of parallaxes."
The list included eleven fainter stars with notable proper motions, and most of these proved to have fairly large parallaxes.
These successes led to renewed zeal, and now the distances of many stars are known more or less accurately. Several of the brightest stars, which might be expected to be the nearest, have not shown a parallax amounting to a twentieth of a second of arc. Among these are Canopus, alpha Orionis, alpha Cygni, beta Centauri, and gamma Cassiopeia. Oudemans has published a list of parallaxes observed.
Brinkley, Director of the Dublin College Observatory, turned on the same subject. Brinkley, who was in possession of a first-rate meridian-circle, believed himself to have discovered relatively large parallaxes for four of the brightest stars; Pond, relying on the testimony of the Greenwich instruments, asserted their nullity.
The distances even of the few stars found to have measurable parallaxes are on a scale entirely beyond the powers of the human mind to conceive. In the attempt both to realize them distinctly, and to express them conveniently, a new unit of length, itself of bewildering magnitude, has originated. This is what we may call the light-journey of one year.
When it is added that a few star-couples had been noted in singularly, but it was supposed accidentally, close juxtaposition, and that the failure of repeated attempts to measure stellar parallaxes pointed to distances at least 400,000 times that of the earth from the sun, the picture of sidereal science, when the last quarter of the eighteenth century began, is practically complete.
So far as measurement goes, we can only say of the distances of all the stars, except the few whose parallaxes have been determined, that they are immeasurable.
Chloe was an ordinary mortal negress enough, but Diana might have been the Huntress of the Woods herself, done into the African type. I have known young American school girls, duly instructed in the nature of the parallaxes of the stars, but, as a rule, they do not know how to darn their stockings.
In the arduous matter of determining star distances progress has been steady, and bids fair to become rapidly accelerated. Together, yet independently, Gill and Elkin carried out, at the Cape Observatory in 1882-83, an investigation of remarkable accuracy into the parallaxes of nine southern stars.
Of 450 objects thus cursorily examined, only one star of the seventh magnitude, numbered 1,618 in Groombridge's Circumpolar Catalogue, gave signs of measurable vicinity. Similarly, a reconnaissance among rapidly moving stars lately made by Dr. Chase with the Yale heliometer yielded no really large, and only eight appreciable parallaxes among the 92 subjects of his experiments.
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