Popular Science Monthly/Volume 12/November 1877/The System of Sirius




EACH of the stars which glitter in the depths of space is a voluminous and massive sun like that which gives light to our earth. Distance alone reduces them to the appearance of fixed points. If we could approach any one of them we should experience the same impression as in passing from Neptune to the sun; the star would increase in size as we should approach it; it would soon exhibit a circular disk and continue to increase its proportions until they would be as large as the sun; finally, this luminous disk, continuing to increase in consequence of our approach, would expand and present itself as a fiery furnace filling the entire heavens—a colossal blaze, under which we would be reduced to nothing, melted like wax, vaporized like a drop of water dropped on red-hot iron! Such is every star in the heavens.

Each sun in space has its special sphere of attraction, a sphere which extends to the limit of neutralization by another. This attraction diminishes in the inverse ratio of the square of the distances, but never becomes absolutely nothing. At the distance of Neptune the solar attraction is 900 times less than at the distance of the earth. While the earth if it were stopped in its course would fall toward the sun 294 hundred-thousandths of a metre during the first second of time, Neptune would fall only 327 hundred-millionths of a metre in the same time. At the aphelion distance of the comet of 1680 the fall toward the sun is only the minute distance of 416 hundred-billionths of a metre during the first second of time. This attraction continues thus to decrease as the distance increases. But, at the same time, if a body moves in the direction of one of the neighboring stars, it begins immediately to receive its influence. The star nearest us is at a distance 210,000 times greater than that which separates the earth from the sun, or eight trillions of leagues; it is the star Alpha Centauri, a brilliant double star whose orbit and mass I have calculated. This mass is equal to the half of that of the sun; it happens that if one could travel from the sun to this star a point would be reached where the attraction of the two would neutralize each other; this point is three-quarters of the distance which separates us, that is, six trillions of leagues from our sun, or, what is the same, two trillions of leagues from Alpha Centauri, the whole distance being eight trillions. At that point, a celestial body, a comet, would hesitate as to which course to pursue, would weigh nothing, would stop in its flight; but the feeblest outward influence would be felt, throwing it either into the sphere of attraction of our sun or into that of Alpha Centauri.

This sun called Centaurus is located in the southern sky, near the antarctic pole. It appears to us in the form of a bright star of the first magnitude. The sun nearest to us, next after this, is situated in the northern sky, in the constellation Cygnus, or the Swan. It is famous as 61 Cygni. Its distance is 400,000 times the radius of the earth's orbit, or about fifteen trillions of leagues. I have often observed this star: it is just visible to the naked eye, but to the telescope it is double, as the preceding, only its components do not move around each other, a conclusion which has much surprised me, although arrived at by comparing all the observations made during the last hundred years; its mass, therefore, cannot be determined. But, however that may be, the fact which should impress us is that the distances which separate the suns of the universe are reckoned not by millions, nor by billions, but by trillions of leagues.

The most brilliant star of our sky, Sirius, is a sun whose volume, judging from its light, should be 2,600 times larger than that of our sun. Its distance is about 897,000 times thirty-seven millions, that is about thirty-three trillions of leagues.

Let us mention again among "our neighbors" the sixty-second of Ophiuchus, situated near the equator. I have calculated that it weighs about three times as much as our sun, that is, 900,000 times more than the earth. Its distance is 1,400,000 times the semi-diameter of the earth's orbit, that is, fifty-four trillions of leagues.

Astronomers, since the time of Kepler, agree in admitting that each of the countless suns that fill infinite space is the centre of a system analogous to the planetary system of which we form a part. Each of these suns that we see in the sky shows to us a luminous fireside around which other human families are gathered. Our eyes are too feeble to see these unknown planets. The most, powerful of our telescopes do not yet reach down to these depths. But Nature concerns itself neither with our eyes nor with our telescopes, and so, beyond the boundaries that stop the flight of our tired conceptions, she continues to display her boundless and magnificent works.

However, the hour has come when these planetary systems different from ours cease to slumber in the domain of hypothesis. In spite of the telescope, celestial mechanics have already revealed the existence of obscure stars, invisible in the rays of these distant suns, but which affect them in their proper movements across immensity; and already powerful telescopes have contemporaneously recognized several among the stars known before to exist only in hypothesis.

One of the most splendid conquests of sidereal astronomy has been the discovery of the system of Sirius, made some fifteen years since. For a long time, from careful measures of its position, it has been remarked that this brilliant star is slowly moving in space, like all the other stars, but that its proper movement is not uniform; and Bessel announced, thirty years ago, that at some time there would be discovered, without doubt, a world of its system moving around it and disturbing it in its progress. This discovery was made in 1862. The companion of Sirius was then almost exactly on the eastern side, quite small, and buried in the rays of the star. Since that year it has been constantly watched by the aid of powerful instruments, and it is seen to slowly gravitate around the Sirian sun.

But this companion certainly does not follow the theoretic orbit calculated to correspond to the perturbations noted in the proper movement of the brilliant star. Differences more and more marked are shown between the calculated ellipse and the observed ellipse. The following is the orbit calculated by the German astronomer Auwers in 1864 to correspond with recognized perturbations:

Passage by lower apsis 1793.890
Annual movement 70.28475
Period years 49.418
Eccentricity 0.6010

The last orbit calculated by Auwers, placed in the form of the orbits of double stars, and given as definitive, is the following:

Perihelion passage 1843.275
Longitude of node 61°.57,8
Angle between node and perihelion 18°.54,5
Inclination 47°.8,7
Eccentricity 0.6148
Semi-major axis 7".331
Period years 49.399

From these elements, the limits of distance ought to be 2.31" at 302.5° in 1841, and 11.23" at 71.7° in 1770, and the ephemeris is—

1862 85°.4 10".10 1874 65°.0 10".95
1865 79°.9 10".78 1876 62°.1 10".59
1868 75°.0 11".15 1878 58°.4 10".05
1871 70°.3 11".20 1880 54°.2 9".33

But, in making out my "Catalogue of Double Stars in Movement," I have found that all the observations on the satellite of Sirius give the following means for each year since its discovery:

1862 84°.6 10".08 1870 65°.0 12".06
1863 82°.2 9".84 1871 63°.0 11".79
1864 79°.0 10".33 1872 61°.3 11".34
1865 76°.7 10".56 1873 62°.7 11".33
1866 75°.0 10".61 1874 58°.5 11".18
1867 73°.9 10".39 1875 55°.5 11".30
1868 70°.4 11".18 1876 55°.2 11".51
1869 72°.3 10".92 1877 51°.0 11".40

Pardon these figures! But they form the basis of the reasonings which constitute the groundwork of this article, and it is essential to consider them in order to know on what to rely in discussing the system of Sirius. In comparing these last numbers with those of the preceding ephemeris, we see at the first glance that the angle diminishes more rapidly than had been announced, while the distance has continued to increase since 1870 instead of having attained its maximum on that year, as the orbit of Auwers indicated. It is still further shown by the diagram I have constructed that the arc of the observed orbit crosses the calculated orbit about 1668 and is projected outside of it, pursuing a wholly different curve which must be larger than the orbit traced and less eccentric.

If the observed motion were the mean motion, the revolution of the satellite would be accomplished in a period of about one hundred and sixty-seven years. But the arc passed is yet too small to allow any positive conclusion, and, as the observed perturbations of Sirius demand a period of forty-nine years, we are brought to the conclusion that the observed companion continues to accelerate its motion and will be found in the west of Sirius in 1892, or else there is another body causing perturbation nearer Sirius, and moving more rapidly.

We should reserve all conclusions in regard to the existence of these other satellites, as well as all difference of period between the observed orbit and the calculated orbit; but the inevitable conclusion is, that the observed positions do not correspond with those of the ephemeris, and that the orbit thence resulting differs from the calculated orbit.

By the aid of all the observations I have constructed the figure, which shows the movement of the observed planet from 1862 to 1877. The central disk represents Sirius; the four cardinal points are indicated by dotted lines; the proper movement of Sirius in space is marked by the large arrow, whose length corresponds exactly to this movement during ten years (the figure is drawn to the precise scale often millimetres for a second). If the small star discovered in 1862 to the east of Sirius did not belong to it, if it was situated in the depths of space far beyond, it would have remained fixed, and Sirius would have moved from it in the direction indicated by the arrow. But, on the contrary, it belongs to Sirius, accompanies that sun in its progress as the earth accompanies its sun, and turns around it in an elliptic orbit. It has yet traversed, from 1862 to 1877, only the line marked on the figure—a curve not long enough to enable us to calculate the remainder of its orbit. As it is seen, this star is quite small by the side of Sirius, but still larger than Jupiter relatively to our sun. Is it an immense planet, totally opaque and shining only by reflection of the light of Sirius? This is not probable; it must still be self-luminous just as our own earth was during so many ages. It does not correspond exactly to the observed perturbations, a fact which

PSM V12 D061 Orbit of sirius.jpg

proves that the system of Sirius certainly contains other worlds yet unseen. Our lamented friend Goldschmidt believed he saw three other planets. Thus, in conclusion, we have a solar system, outside of our own, as an object of study.

We know a great number of stars which are accompanied by smaller stars moving around them like the earth around the sun. These systems, which are now numbered by hundreds, have been so carefully observed that we have been able to calculate the orbits and periods of the planets, brilliant or opaque, which compose them.

It is, then, no longer on mere hypothesis that we can speak of solar systems other than our own, but with certainty, since we already know a great number, of every order and of every nature. Single stars should be considered as suns analogous to our own, surrounded by planetary worlds. Double stars, of which the second star is quite small, should be placed in the same class, for this second star may be an opaque planet reflecting only the light of the large one, or a planet still giving out heat and light. Double stars of which the two components give the same brightness are combinations of two suns around each of which may gravitate planets invisible from this distance; these are worlds absolutely different from those of our system, for they are lighted up by two suns, sometimes simultaneous, sometimes successive, of different magnitudes, according to the distances of these planets from each of them; and they have double years of which the winter is warmed by a supplementary sun, and double days of which the nights are illuminated, not only by moons of different colors, but also by a new sun, a sun of night!

Those brilliant points which sparkle in the midnight sky, and which have, during so many ages, remained as mysteries in the imagination of our fathers, are therefore veritable suns, immense and mighty, governing, in the parts of space lighted by their splendor, systems different from that of which we form a part. The sky is no longer a gloomy desert; its ancient solitudes have become regions peopled like those in which the earth is located; obscurity, silence, death, which reigned in these far-off distances, have given place to light, to motion, to life; thousands and millions of suns pour in vast waves into space the energy, the heat, and the diverse undulations, which emanate from their fires. All these movements follow each other, interfere, contend, or harmonize, in the maintenance and incessant development of universal life.

  1. Translated from the French by P. A. Towne.