Page:Astronomy for Everybody.djvu/222

One of these bodies is so exceptional as to attract our special attention. All the hundreds of minor planets known up to 1898 moved between the orbits of Mars and Jupiter. But in the summer of that year Witt, of Berlin, found a planet which, at perihelion, came far within the orbit of Mars—in fact within fourteen million miles of the orbit of the earth. He named it Eros. The eccentricity of its orbit is so great that at aphelion the planet is considerably outside the orbit of Mars. Moreover the two orbits, that of the planet and of Mars, pass through each other like two links of a chain, so that if the orbits were represented of wire they would hang together.

Owing to the inclination of its orbit, this planet seems to wander far outside the limits of the zodiac. When nearest the earth, as it was in 1900, it was for a time so far north that it never set in our middle latitudes, and passed the meridian north of the zenith. This peculiarity of its motion was doubtless one reason why it was not found sooner. During its near approach in the winter of 1900-‘01 it was closely scrutinised and found to vary in brightness from hour to hour. Careful observation showed that these changes went through a regular period of about two and a half hours. At this interval it would fade away a little with great uniformity. Some observers maintained that it was fainter at every alternate minimum of light, so that the real period was five hours. It was supposed that this indi-