646 POPULAR SCIENCE MONTHLY. 



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 ad- 

 vantage 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 magni- 



<lo* 



Fig. 2. Orbits of Eros, Earth and Mars. Relative Positions of Eros and Earth. 



tude. 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 



