160 SOME RECENT ASTRONOMICAL EVENTS. 



So highly eccentric indeed was the planet's orbit that, although 

 upward of 90,000,000 miles distant at unfavorable oppositions, when 

 nearest the earth it may come within about 15,000,000 miles, and 

 is on these occasions, so far as is known, our nearest celestial neigh- 

 bor after the moon. This peculiarity caused the planet to become an 

 object of great interest on account of its possible use in the more 

 accurate determination of the sun's distance from the earth, for an 

 object at 15,000,000 miles distance has a very appreciably different 

 position among the stars if viewed from opposite ends of the earth's 

 diameter — no less a parallax indeed than 100 seconds of arc. Con- 

 sequently its actual distance from the earth could probably be deter- 

 mined with very great accuracy, and this distance when thus fixed 

 could be used indirectly to obtain a new estimate of the sun's distance 

 from the earth, with an accuracy possibly exceeding that of earlier 

 methods. 



Search was immediately instituted by Prof. E. C. Pickering, the 

 director of Harvard College Observatory, through the continuous 

 photographic record of the stars which is kept up at that observatory, 

 for earlier positions of the planet, and such were soon found among 

 plates taken in 1893, 1891, and 1896. From these observations, which, 

 taken with those made in 1898, follow the planet through a consider- 

 able range of time, a very accurate orbit was computed. 11 



The orbits of Eros and the earth were found to be of such a form 

 that their next reasonably close approach would occur in November, 

 1900, and while their distance at this time was indeed considerably 

 greater than their least possible distance of 15,000,000 miles, yet it 

 was determined to institute at that opposition a thorough parallax cam- 

 paign to be taken part in by all the observatories in the world fitted 

 with instruments suitable for this purpose, for it would be necessary 

 to wait upward of twenty years for the minimum distance to occur. 

 Fully 50 observatories took part in this parallax campaign, continu- 

 ing observations from October through to about the 1st of February. 

 These observations were in part photographic, in part visual, and 

 taken at stations as far apart as the Cape of Good Hope, South Africa, 

 and Helsingfors, in Finland, and indeed it might almost be said that 

 there was no habitable quarter of the earth which was not represented 

 by observers. It is yet too early to say what will be the results, but 

 it is hoped that they may lead to a very excellent determination of the 

 distance of the sun. 



11 As an evidence of the value of the photographic records of Harvard College 

 Observatory, it was recently remarked by Professor Pickering that "if, in the future, 

 any other object like Eros should he discovered, we have at this observatory the 

 means of tracing its path since L890, during the time in winch it was moderately 

 bright, with nearly as great accuracy as if a series of observations had been taken of 

 it with a meridian circle," 



