238 ANNUAL REPORT SMITHSONIAN INSTITUTION, 195 6 



Owing to its proximity Phobos cannot be seen from the Martian 

 polar regions, as it is always hidden by the curvature of the surface of 

 Mars. In the equatorial zone it passes overhead, and must look con- 

 siderably larger when high up in the sky that when near the horizon. 

 A few moments' thought will be sufficient to show that Phobos is 

 considerably nearer when overhead, and therefore looks as big as it 

 possibly can. 



If Mars is inhabited by intelligent beings, and if they have tele- 

 scopes of equal power to ours, it would be easy to find out whether 

 these little moons also are inhabited. The rarefied atmosphere would 

 enable high powers to be used, bringing Phobos within a mile and 

 Deimos to within four miles. However, both moons are certainly 

 barren worlds, being devoid of atmospheres and appreciable surface 

 gravity. They would be admirably suitable for observatories, and 

 may be used as such during the coming era of space travel. What a 

 view of Mars could be obtained from Phobos ! Seen from this little 

 world Mars would look over 80 times larger than the moon does to us, 

 and would go through all its phases in less than eight hours. 



To ourselves Mars does not always look round, but may appear 

 gibbous, that is to say like the moon three days before or after full. 

 At such times we can see a little bit of the darkened or night side of 

 Mars. Along the line dividing the darkened from the sunlit portion 

 of the planet (the "terminator," to use the correct and technical term), 

 the sun is either rising or setting. This line is generally smooth, but 

 occasionally is irregular owing to the presence of bright projections 

 or spots. When such are seen they can only be viewed for a short time 

 before being carried into the bright or the darkened portion, owing to 

 the rotation of Mars on its axis. Although fiction writers, for exam- 

 ple H. G. Wells in his fantasy The War of the Worlds, have ascribed 

 these bright spots to flashes from a stupendous gun which was being 

 used by the Martians to project cylinders to the earth, there is no doubt 

 that they are clouds floating in the Martian atmosphere at a consider- 

 able distance above the surface and thus catching the sun's rays. 



But there are other bright spots, not floating in the atmosphere but 

 on the surface. They appear in the equatorial regions during the 

 summer and autumn on Mars. Usually they lie on or close to the 

 borders of one or more of the patches of vegetation, such as Syrtis 

 Major or Margaritifer Sinus. These white spots develop markedly 

 during the hot season, and, although we are not sure what they are, the 

 plausible suggestion has been made that they may be cultivated areas 

 or, in other words, crops. 



Certain canals occasionally show activity of another kind ; they be- 

 come double! What was previously seen as a long, linear marking 

 now has a companion running parallel to it a short distance away. 

 They look exactly like a rail track, and may maintain their parallel 



