SCIENCE. 



563 



EPHEMERIS 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 favor- 

 able 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 tele- 

 scopes, 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 declination 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 

 measures of the diameter of the planet were made by ob- 

 servers with good telescopes which showed curious dif- 

 ferences both between themselves and when compared 

 with the results obtained from the heliometer. Some of 

 these measures seemed to show an appreciable flattening 

 at the poles, while others showed no such flattening. It 

 will be interesting to have these measures repeated dur- 

 ing 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 12% inch refractor of 

 the Morrison Observatory, and were seen with other in- 

 struments. Before December ist of this year the satel- 

 lites will be considerably brighter than when last ob- 

 served 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 mod- 

 erate size. 



The following ephemeris (derived from the elements of 

 Prof. A. Hall, A. N. No. 2394) has been computed at the 

 requtst of several observers, and will be found convenient 

 for any who may wish to observe these satellites. In 

 connection with the discussion of the relative merits of 

 reflectors and refractors, excited by the observations of 

 these satellites, it may be interesting to many to try if 

 they can see them. 



In the case of Deimos, the outer satellite, the ephem- 

 eris gives the Washington mean times of the east and 

 west elongations, together with the position-angle and 

 distance at the time of elongation. In the case of Phobos 

 on.y the times of western elongations are given, as the 

 revolution time is very short and the times of eastern 

 elongations may be obtained by a simple interpolation. 

 The aberration time is not included in the time given, 

 but it may be taken from the table at the end if desired, 

 the effect of the aberration being to make the satellites 

 about five minutes late at each elongation. The relative 

 brightness on diffeient days maybe obtained from the 

 same table, taking the brightness on Nov. 20 as unity. 

 As was shown by the observations of 1879, Prof. Hall's 

 elements are very nearly correct, so that the correction to 

 this ephemeris will be quite small. 



* Read before the St. Louis Academy of Sciences. 



Deimos. 



Date. 



Direction of 

 Elongation. 



Wash. 

 M. T. 



Pos. 

 Ang. 



Dist. 



Date. 



Direction of 

 Elongation. 



Wash. 

 M. T. 



Pos. 

 Ang. 



Dist. 







H. M. 











H. M. 







Dec. 5 



E 



16 33 







! Dec. 22 



E 



2 2 







6 



W 



7 42 













W 



17 10 











E 



22 50 







23 



E 



8 19 







7 



W 



•3 38 









W 



23 26 







8 



E 



5 7 







24 



E 



'4 33 









W 



20 14 



250°2 



52". 4 



25 



W 



5 4' 











9 



E 



11 23 









E 



20 49 







10 



W 



2 31 







26 



w 

 w 



11 57 









E 



17 39 







27 



E 



3 5 







I I 



W 



8 47 









w 



18 12 









E 



"3 55 







28 



E 



9 20 







12 



W 



■5 3 







29 



W 



28 







13 



E 



6 11 









E 



'5 36 









W 



.21 19 



249°. 7 



53"-2 



3° 



W 



6 44 





.... 



'4 



E 



12 27 









E 



21 52 







15 



W 



3 35 







r 3 ' 



W 



13 









E 



'8 43 







Jan 1 



E 



4 7 







16 



W 



9 ji 









W 



19 15 



245°-9 



52" -4 





E 











2 



E 



10 23 









w 



16 7 







3 



w 



• 3" 







18 



E 



7 '5 









E 



16 39 









W 



22 23 







4 



W 



7 47 







19 



E 



•3 3' 









E 



22 55 







20 



W 



4 39 



248°.S 



53'-7 



5 



W 



'4 3 









E 



19 47 







6 



E 



5 11 







21 



W 



10 54 









W 



20 19 







Phobos. 



Date. 



Wash 

 M. T. 



Pos. 

 Ang. 



Dist. 



Date. 



Wash. 

 M. T. 



Pos 

 Ang. 







Dist. 



Dec. 2 



H. M. 

 I 40 

 9 19 



16 58 



37 

 8 16 



25'°-5 



20". 3 



Dec . 20 



II. M. 



5 5i 

 13 30 

 21 g 



4 48 

 12 27 

 20 6 



248°. 5 



21". 5 

















3 







21 





















15 56 

 23 35 

 7 14 

 I 4 53 



22 32 



6 12 



'3 5i 

 21 31 

 5 'o 











---- 









22 



3 46 







4 



















23 



11 25 

 19 4 

 2 43 

 10 22 

 18 1 







5 

















24 



1 40 



9 19 

 16 58 



37 

 8 16 







6 













12 49 

 20 28 



4 7 

 11 46 

 '9 25 



3 S 

 10 44 

 18 23 

 . 2 2 













7 







25 







8 



25°° ■ 4 



20" .9 



26 



'5 55 

 23 34 



7 '3 

 14 53 

 22 32 



6 11 



'3 5° 

 21 29 

 5 8 

 12 47 

 20 26 



4 5 

 11 44 



19 23 

 3 3 

 )o 42 

 18 21 



247-°3 



2l".4 

























9 







27 









9 4i 

 17 20 

























10 



5( 







28 









8 39 

 16 18 

























1 1 



23 57 

 7 36 

 15 15 

 22 54 



6 33 

 14 13 







29 















30 







12 

























21 52 

 5 3« 

 13 10 







31 



2 







13 







9 39 

 17 18 



57 



8 36 

 .6 15 

 23 54 



7 33 

 '5 13 

 22 52 



6 3i 

 14 10 

 21 49 



5 28 

 '3 7 

 20 46 



4 25 ' 

 12 4 

 ■9 43 



3 23 

 1 1 2 

















'4 



20 49 

 3 28. 

 12 7' 

 19 46 



3 25 



*J * 

 18 43 



2 23 

 IO 2 



249° -7 







21-.3 



Jan. 1 



246. °o 



21". I 



15 





2 

















16 





3 

















17 41 











17 



I 20 





4 







8 59 

 16 38 











18 



17 







5 







7 56 

 ■5 35 

 23 14 



6 53 

 '4 33 



















6 







19 



















18 41 



2 20 









22 12 







7 





















