PRITCHETT EPHEMERIS OF SATELLITE OF MARS, lObl. 353 



Efhemeris of the Satellites of Mars for the Opposition 



of 1881. 



By H. S. Pritchett. 



Owing to the greater distance from the Earth and the Sun the 

 present opposition of Mars will not be so favorable as the two 

 preceding ones ; still these distances will be sufficiently small to 

 permit many useful observations of physical phenomena, and, in 

 the case of large telescopes, observations of the satellites. In one 

 respect the planet is much more favorably situated than in the 

 former oppositions referred to, since it reaches this year a decli- 

 nation of 26° north and hence will be observed at a much higher 

 altitude. Physical observations, either measures or drawings, 

 by amateur astronomers with good glasses, if carefully made and 

 published, will be useful when finally reduced and compared. 



During the last opposition several series of micrometric meas- 

 ures of the diameter of the planet were made by observers with 

 good telescopes which showed curious differences both between 

 themselves and when compared with the results obtained from 

 the heliometer. Some of these measures seemed to show an ap- 

 preciable flattening at the poles, while others showed no such 

 flattening. It will be interesting to have these measures repeated 

 during the present opposition, with a careful discussion of the 

 sources and effects of personal error. 



The satellites were observed last opposition with at least one 

 of the large reflectors, with the great refractor at Washington, 

 with the 15-inch refractor of the Harvard College Observatory, 

 and with the I2i-inch refractor of the Morrison Observatory, and 

 were seen with other instruments. Before December ist of this 

 year the satellites will be considerably brighter than when last 

 observed in 1879 with the Harvard College refractor, and also 

 brighter than when last observed with the Morrison Observatory 

 refractor. It seems possible, therefore, that they may be seen 

 this year with telescopes even of moderate size. 



The following ephemeris (derived from the elements of Prof. 

 A. Hall, A. N. No. 3394) has been computed at the request of 

 several observers, and will be found convenient for any who may 

 wish to observe these satellites. In connection with the discus- 



