When these have been given with a reasonable approach to accuracy, the observer has done his best to provide a real, though small, contribution to the sum of human knowledge; nor is the determination of these points so difficult as would at first appear from their number. The fixing of the points of appearance and disappearance and of the radiant will present a little difficulty to start with; but in this, as in all other matters, practice will bring efficiency. It may be mentioned that the efforts of those who take up this subject would be greatly increased in usefulness by their establishing a connection with the Meteor Section of the British Astronomical Association.
One curious anomaly has been established by Mr. Denning's patient labour—the existence, namely, of what are termed 'stationary radiants.' It is obvious that if meteors have the cometary connection already indicated, their radiant point should never remain fixed; as the showers move onwards in their orbit they should leave the original radiant behind. Mr. Denning has conclusively proved, however, that there are showers which do not follow the rule in this respect, but proceed from a radiant which remains the same night after night, some feeble showers maintaining the same radiant for several months. It is not easy to see how this fact is to be reconciled with the theory of cometary origin; but the fact itself is undeniable.
CHAPTER XIV
THE STARRY HEAVENS
We now leave the bounds of our own system, and pass outwards towards the almost infinite spaces and multitudes of the fixed stars. In doing so we are at once confronted with a wealth and profusion of beauty and a vastness of scale which are almost overwhelming. Hitherto we have been dealing almost exclusively with bodies which, though sometimes considerably larger than our world, were yet, with the exception of the sun, of the same class and comparable with it; and with distances which, though very great indeed, were still not absolutely beyond the power of apprehension. But now all former scales and standards have to be left behind, for even the vast orbit of Neptune, 5,600,000,000 of miles in diameter, shrinks into a point when compared with the smallest of the stellar distances. Even our unit of measurement has to be changed, for miles, though counted in hundreds of millions, are inadequate; and, accordingly, the unit in which our distance from the stars is expressed is the 'light year,' or the distance travelled by a ray of light in a year.
Light travels at the rate of about 186,000 miles a second, and therefore leaps the great gulf between our earth and the sun in about eight minutes. But even the nearest of the fixed stars—Alpha Centauri, a star of the first magnitude in the Southern Hemisphere—is so incredibly distant that light takes four years and four months to travel to us from it; while the next nearest, a small star in Ursa Major, is about seven light-years distant, and the star 61 of the constellation Cygnus, the first northern star whose distance was measured, is separated from us by two years more still.
At present the distances of about 100 stars are known approximately; but it must be remembered that the approximation is a somewhat rough one. The late Mr. Cowper Ranyard once remarked of measures of star-distances that they would be considered rough by a cook who was in the habit of measuring her salt by the cupful and her pepper by the pinch. And the remark has some truth—not because of any carelessness in the measurements, for they are the results of the most minute and scrupulous work with the most refined instrumental means that modern skill can devise and construct—but because the quantities to be measured are almost infinitely small.
It is at present considered that the average distance from the earth of stars of the first magnitude is thirty-three light years, that of stars of the second fifty-two, and of the third eighty-two. In other words, when we look at such stars on any particular evening, we are seeing them, not as they are at the moment of observation, but as they were thirty-three, fifty-two, or eighty-two years ago, when the rays of light which render them visible to us started on their almost inconceivable journey. The fact of the average distance of first-magnitude stars being less than that of second, and that of second in turn less than that of third, is not to be held as implying that there are not comparatively small stars nearer to us than some very bright ones. Several insignificant stars are considerably nearer to us than some of the most brilliant objects in the heavens—e.g., 61 Cygni, which is of magnitude 4·8, is almost infinitely nearer to us than the very brilliant first magnitude star Rigel in Orion. The rule holds only on the average.