Page:Popular Science Monthly Volume 58.djvu/654

646 nearer to Mars than to the earth. Owing to the large inclination of the planes of the two planets, and the unfavorable position of the line in which the planes intersect, this is not the case, as was pointed out by Mr. Crommelin. Eros does not approach Mars nearer than twenty million miles, so that the Martians, if such exist, have no advantage in this line of research.

At his approach in 1894, the brightness of Eros was computed by Professor Pickering to have been about the seventh magnitude. This places it just beyond the reach of the naked eye, even at the most favorable oppositions. During the recent opposition Eros was thirty million miles distant, and fainter than the ninth magnitude.

E. von Oppolzer has recently announced that Eros undergoes, within a few hours, variations in light amounting to a whole magnitude.

This variation has been confirmed at the Harvard Observatory, where there are observations, visual and photographic, extending back over eight years, sufficient to establish the period with precision. The variability of Eros is doubtless due to its axial revolution, and may be caused by the unequal light-reflecting power of different parts of its surface.

From the elements and diagram, it may be seen that the distance from perihelion, or the point nearest the sun, to the descending node, or the point where the planet passes through the plane of the earth's orbit, is less than three degrees. This is fortunate, for otherwise the planet's distance would be increased. The longitude of the planet's perihelion is 121°. The earth's longitude—or the sun's longitude, as seen from the earth, plus 180°—is 121° on January 21. In 1894, the