188 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1926 
late about a mean position. The sun and the stars appear to file 
slowly back of it, while all the time we can see it rotating upon its 
own axis and changing phase, like our moon, with the varying position 
of the sun from which it receives its illumination. The position in 
the sky where the earth will be seen changes with the position of the 
observer. From the central region of the lunar disk visible from the 
earth, it is enthroned in the lunar zenith. At the periphery, it will 
be seen on the horizon. (Pls.3and4.) In each position, it will have 
an aspect thirteen times greater than that of our moon. At the time 
it is full it will shine with intense brilliancy. 
Let us now leave this strange world, so near to us—only 384,000 
kilometers (239,000 miles) distant. It is the excursion outside of 
the earth about which we can foretell the most. The facts we pos- 
sess about the other planets of the solar system are fewer, and to 
avoid pure phantasy we must limit ourselves to more general con- 
siderations. Let us remember that with regard to the worlds which 
we are to consider, though the facts relative to the appearances 
in the sky are exact, coming from mathematical deductions of 
measures, further than that we can offer only details which seem 
reasonable. We can not, for instance, say: Behold a landscape of 
the planet Mars! but, rather, a landscape which is theoretically 
possible on the planet Mars; or, better yet, what we conceive should 
be certain landscapes upon that planet. 
The “fixed stars” are so distant that their relative positions 
appear the same from whatever planet they are observed. There- 
fore, for each of these worlds the starry firmament would be the 
same as ours. However, from each one the other planets are seen 
with differing brightness, there are different moons, and, finally, 
the sun appears of very different size (pl. 5). 
Thus from Mercury, the planet closest to the sun, this central 
star appears enormous, in such proportions as Plate 5 indicates. 
Further, this great size varies notably because the orbit of Mercury 
is very eccentric. The apparent diameter of Mercury’s sun indi- 
cated (relative to that seen from the earth) is that when Mercury 
is in perihelion; that is, when it is nearest to the sun. What man- 
ner of landscape is lighted by this colossal furnace the heat of which 
we are certainly not so constituted as to be able to bear, especially 
since it stays immovable in the sky? For Mercury revolves about 
the sun, always turning the same side toward it. In order to enjoy 
the freshness of night we would have to travel around into the 
opposite hemisphere. 
Our knowledge about this planet is insignificant. Probably its 
surface has high mountains, but we can not estimate the importance 
of its atmosphere. Let us not delay upon this inhospitable world, 
