« AnteriorContinuar »
every year? This is the last question, and even this has not escaped the successful examinations of the human mind. The discovery of the parallax of one or two fixed stars has already been referred to.Within a few months, an elaborate work, by Struve, on the Sidereal Heavens, has reached us, containing some remarkable investigations on the mean distances of the stars of the various magnitudes.
Struve, by a most ingenious and powerful train of investigation, obtains a series representing the relative mean distances of the stars of all magnitudes, up to the most minute visible in Herschel's twenty feet reflector. From the sun, as a centre, he sweeps successive concentric spheres, between whose surfaces he conceives the stars of the several magnitudes to be included. The radius of the first sphere reaches to the nearest stars of the first magnitude; that of the second sphere extends to the farthest stars of the same magnitude, and the mean of these two radii will be the mean distance of the stars of the first magnitude. The same is true with reference to the concentric spheres embracing within their surfaces the stars of the various orders of brightness.
Having, from his data, computed a table exhibiting the relative distances of the stars of the different magnitudes, an examination of these figures revealed the singular fact that they constituted a regular geometrical progression; and having assumed the distance of the stars of the sixth magnitude as the unit the distance of the stars of the fourth magnitude will be one-half ; that of those of the second magnitudo will be one-quarter, and so of the even numbers expressing magnitude ; while the distance of the stars of the fifth magnitude is obtained by dividing unity by the square root of the number 2, and from this the distances of the odd magnitudes come by dividing constantly by 2. In mathematical language, the distances of the stars of the various magnitudes form a geometrical progression whose ratio is equal to unity divided by the square root of 2.
Having thus obtained the relative mean distances of the stars, in case we can find the absolute mean distance of those of any one class, that will reveal to us the absolute mean distances of the stars of every class. For the approximate accomplishment of this last great object, we are again indebted to the as tronomers of Russia. As early as 1808, M. Struve, then of Dorpat, attempted the determination of the parallax of a large number of stars, and obtained results so small that, in the state of astronomical science as it then existed, no confidence could be placed in them. The final value of the numerical co-effi cient of the aberration of light had not been then absolutely determined. Subsequent investigations by Struve and Peters have fixed this quantity, and the actual determination of the parallax of eight stars recently, has shown that confidence may now be placed in the results obtained by Struve nearly 25 years ago.
By combining all the results, M. Peters finds no less than thirty-five stars whose parallaxes have now been determined, either absolute or relative, with a degree of accuracy which warrants their employment in investigating the problem of the mean parallax of stars of the second magnitude. Excluding from this number the stars 61 Cygni, and No. 1830 of the
Grombridge catalogue, on account of their great proper motion, there remained thirty-three stars to be employed in the investigation.
From a full and intricate examination of all the data, by a process of reasoning which I will not attempt to explain at this time, M. Peters finds the mean par allax of stars of the second magnitude to be equal to 116 thousandths of one second of arc, with a probable error less than a tenth part of this quantity. Returning now, with this absolute result, to the table of the relative distances of the fixed stars of different magnitudes, it is easy to fix their absolute distances, as far as confidence can be placed in this first approximation. We find the stars of the first magnitude to be located between the surface of two spheres, whose radii are respectively nine hundred and eightysix thousand times the radius of the earth's orbit, and one million two hundred and forty-six thousand times the same unit. We will express the distance in terms of the velocity of light, as no numbers can convey any intelligible idea. Stars of the first magnitude send us their light in about seventeen years ; those of the second magnitude in about thirty years; -stars of the third magnitude send their light in about forty-five years; those of the fourth magnitude in sixty-five years; those of the fifth in ninety years; those of the sixth magnitude, the most remote visible to the naked eye, send us their light after a journey through space of one hundred and thirty years! while the distance of the lowest order of telescopic stars visible in Herschel's twenty feet reflector is such, that their light does not reach the eye for 3,541 years after it starts on its tremendous journey!
Let it be remembered that these results are not conjectures. Though they are first approximations to the truth, they are reliable to within the tenth part of their value, and are thus far certain ; they raise, in the most astonishing manner, our views of the immensity of the universe, and of the powers of human genius which have fathomed these vast and overwhelming profundities.
Let us now return to the examination of the abso. lute amount of progressive motion of our sun and system through space. As already stated, M. Otho Struve determined its yearly angular motion, as seen from the more distant of the stars of the first magnitude. To convert this angular motion into miles, a knowledge must be obtained of the absolute mean distance of the stars of the first magnitude. This has been accomplished by M. Peters, and combining the researches of Argelander, Struve, and Peters, we are now able to pronounce the following wonderful results. The sun, attended by all its planets, satellites, and comets, is sweeping through space towards the star marked * in the constellation Hercules, with a velocity which causes it to pass over a distance equal to thirty-three millions three hundred and fifty thousand miles in every year !
And now do you demand how much reliance is to be placed on this bewildering announcement? I answer, that as to the reality of the solar motion, there is but one chance out of four hundred thousand that astronomers have been deceived. We cannot resist the evidence, and startling as the truth appears, we are obliged to yield our assent, reluctant though it may be, to the logical reasoning by which this magnificent result has been demonstrated.
But whither is our system tending? If moving on. ward with such tremendous velocity, is there not danger that ere long it may reach the region of the fixed stars, and by sweeping near to other suns and systems, derange the order of the planetary worlds ? Let us examine this question for one moment, on the hypothesis that the sun alone is moving among all the stars of heaven, and that it will hold on in its present direction until it shall reach the star in Hercules, towards which it is now urging its flight. This star is of the third magnitude, and according to our statement already made, the mean distance of its class is such, that its light does not reach us in a period less than forty-six years. Executing the calculation, we find that in case the solar system should continue to progress towards that star, it cannot pass the enormous interval, even at 33,550,000 miles per annum, in less than 1,800,000 years !
If the eye of any superior intelligence can behold this amazing scene, how stupendous must be the spectacle presented! In the centre the sun, blazing with splendor, pursues its majestic career;-around it roll the planets, and about it cluster ten thousand fiery comets. Worlds bright and beautiful hover near the sun ,-worlds fiery and chaotic seek this great centre with impetuous velocity, and then dash away into the farthest range of their grand revolution. But the monarch moves on, and his magnificent cortége, performing his high behests, follow whithersoever he leads through space!
Here we reach the boundary which divides the known from the unknown. Steadily we have purBued the human mind as it has moved on in its grand