The Fixed Stars

Journal of the Minnesota Academy of Science Volume 2 Number 3 Article 10 1881 The Fixed Stars John F. Downey Follow this and additional works at: https://digitalcommons.morris.umn.edu/jmas Part of the Stars, Interstellar Medium and the Galaxy Commons Recommended Citation Downey, J. F. (1881). The Fixed Stars. Journal of the Minnesota Academy of Science, Vol. 2 No.3, 146-161. Retrieved from https://digitalcommons.morris.umn.edu/jmas/vol2/iss3/10 This Article is brought to you for free and open access by the Journals at University of Minnesota Morris Digital Well. It has been accepted for inclusion in Journal of the Minnesota Academy of Science by an authorized editor of University of Minnesota Morris Digital Well. For more information, please contact [email protected]. The Fxcd Stars. THE FIXED STARS. BY PROF. JOHN F. DOWNEY-OF THE UNIVERSITY OF MIN· NESOTA. The object of this paper is to give, in a popular form, a brief review of what is known about the fixed stars. Although they have always been objects of interest, have guided the mariner over trackless seas, arid have inspired many sublime and noble thoughts, yet, until a comparatively recent date, only three things were k.nown about them; viz., that they re tain (approximately) their ·relative positions, that they are self luminous, and that they are very far away. The remotest planet of our own system is at no insignifi cant distance. It is difficult for us to comprehend it when expressed in terms of any unit used in terrestial measurements. The distance from the sun, and consequently the mean dis tance from us, is 2,772,000,000 miles; but miles lose their meaning in such a number. An express train, running day and night, at the rate of thirty miles an hour, would be over ro,soo years in making this journey. Had the ball of the first cannon fired in the Revolutionary War continued in a straight line with the velocity with which it left the muzzle, it would now be only half way to the orbit of Neptune. So far as known this is the confines of our system, with the exception of a number of comets which, in their eccentric orbits, plunge far• beyond. And what a distance it is! It is absolutely awful! Merely to 'think of it almost makes us dizzy. oigitizedbyGoogle · \l l i. ! The Fixed Stars. 147 I- But astronomers were not satisfied when they had reached l r the limits of our own system, and obtained a knowledge of the t· motions of its bodies and the laws by which they are gov erned. Success stimulates the mind and urges it to new ef- · forts and greater achievements. Knowing that our whole ,. planetary system is but a small part of the universe, they were anxious to pass its boundaries, and leap the mighty gulf that separates us from the fixed stars. Many attempts were made, but all in vain; many promising methods were tried, (,.' but to no purpose-until Prussia gave to the world a Bessel, and Bessel it was who led the way across this bewildering dis tance. '·· The distance to the sun is measured by solving the triangle formed by conceiving a line drawn from the sun to the centre of the earth, another from the sun tangent to the earth, and .the radius ofthe earth at the point of tangency. The angle at the sun is the horizontal parallax. As the triangle is right I• angled at the point of tangency, the radius of the earth divided ' by the sine of the parallax will give the distance to the sun. As the different civilized nations will next year repeat their liberality of seven years ago, and send out scientific expedi tions (or observing the transit of Venus, by means of which the sun's parallax is best obtained, we expect a very accurate value of this angle. This method, however, is wholly inapplicable to the measurement of the' distance to the fixed stars; for so great is their distance that the angle at a star subtended by the earth's radius is entirely inappreciable. It was necessary to look for a longer base line. Our annual journey around the sun furnishes one of great length. Now we are 92,000,000 miles on this side of the sun; in six months we shall be 92,- 000,000 miles on the other side: that is, we shall be 184,000, ooo miles from where we now are. Notwithstanding this mighty change, in six months we shall look in the same direc- o;9;,;zed by Coogle The .Fixed Stars. tion for the North Star. Ay, more: so slight is the displace ment that it cannot, by direct measurement, be detected with the most accurate instruments. The English astronomer, Bradley, sought diligently to ascertain the parallax of a star by thus taking direct measurements from the opposite ex tremities of diameters of the earth's. orbit. Though he failed in his object, his labors were re'Yarded with two most bril liant discoveries: viz., nutatio1l, or the oscillation of the ce lestial pole caused by the acti?n of the sun and the moon upon the protuberent equatorial mass, and aberratioll, or the displacement of a celestial body caused by the progressive motion of light in connection with the movement of the earth in its orbit. It was necessary to devise some other method of determin ing the parallax of the fixed stars. Sir Wm. Herschel was the first to attempt to apply one which had been suggested by Galileo. The telescope often reveals two stars where the unassisted eye detects but one. These two stars are not nec essarily near each other, but may appear so only because sit uated nearly in the same straight line with the observer. When one of them is much smaller than the other, it is pre sumably much farther away. Now if the farther one is a little east of the nearer one, a movement on our part toward the east would cause them to separate still farther, and a move ment toward the west would cause them to approach nearer to each other. With such a point of reference, a very slight change could be measured with delicate instruments, and, by 4~ · : .:.'(?: taking several such points of reference, still greater accuracy '":! / ·.: ~ ·· ~~.:· ~ '). ~ .. could be secured. Herschel began his observations upon such a pair or'stars, measuring as frequently as possible and with great care the distance between the two, and noting the direction of the line joining them. Soon a change was observed, but-strange to say-it agreed neither in time nor direction with the motion which parallax would give. Judge / · oigitizedbyGoogle The Fixed Stars. 149 of his astonishment when he discovered that the two stars were revolving around a common center between them. He examined many other pairs with the same result. Thus was the effort to measure a star parallax again defeated; but rich discoveries were rewarding those who were seeking what began to seem as unattainable as the Philoso pher's Stone or the mythical Eldorado. Munich now had her Fraunhofer who had acquired wonderful skill in the construc .· tion of refracting telescopes, and Kcenigsberg had her Bessel who was without a superior in the methematical and astro nomical field. The combined efforts of these two geniuses pro duced the celebrated Kcenigsberg Heliometer. Provided with ·t this wonderfully delicate and ingenious instrument, Bessel undertook the accomplishment of what had baffled his prede cessors. His method differed from Herschel's only in his choosing for points of reference two minute stars that were farther removed from the one whose parallax was sought. After most careful and oft-repeated measurements Bessel detectJd a variation, agreeing exactly in time and direction with what parallax required; but it was so slight and gave such an astounding distance that he hesitat~d. He pursued the investigation through another year and obtained the same result. Still fearing that there might be some mistake, he re peated his observations through another year, and, as the val ue.s were the same, all doubts were dispellt;d, and Bessel announced to the world that he had crossed the hitherto im passable abyss, and measured the distance to one of the fixed stars, 61 Cygni. But how shall we obtain a conception of the amazing distance? l\Iiles, velocities of express trains, and swiftly flying cannon balls, fail to give us an adequate 'unit. Light, which flashes with a swiftness that will carry it eight times around the world while the clock ticks once, occupies nearly ten years in completing this mighty journey. The sub sequent observations of Peters at Pulkova and Johnson at Oxford, have confirmed Bessel's result. Digitized by Coogle 150 The Fixed Stars. There is at least one star, Alpa Centauri, nearer than 61 Cygni, whose light requires three and a half years in coming to us. From Alpha Lyrce the light comes in twelve and a half years; and from Sirius, the brightest star in the heavens, in fourteen years. The light w}th which we shall see the North Star to-night started thirty years ago. If the star Alcyone of the Pleiades should be blotted from existence to night, it would continue to be seen here for five hundred and thirty-seven years; for the light which starts from there to-night cannot reach the earth before the expiration of that time. These distances should be taken with some latitude, as a slight error in so small a parallax makes a great difference in the distance.

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