Simon Newcomb

“ Each of these moves around a planet larger than itself, which it accompanies in its revolution round the sun. A planet not revolving round another is termed a primary planet.
The primary planets are classified as major and minor. The former are eight in number and, with the sun, form the principal members of the solar system, under which head their arrangement is described. The earth on which we live is the third in the order of the major planets from the sun. With respect to the positions of their orbits relative to the earth, the other planets are distinguished as inferior and superior. ”

“ The temperature of the surface of the planet on which the atmosphere rests is determined partly by the sun’s radiation and partly by the temperature of the air. What we should generally expect in the absence of any selective absorption by the air is that the temperature of the lower air would be higher than that of the material surface on which it rests. ”

“ The brilliancy of the planet, as measured by the total amount of light we receive from it, goes through a similar cycle of change. The point of greatest brilliancy is between inferior conjunction and greatest elongation. In the case of Venus this phase occurs about three or four weeks before and after inferior conjunction.
In the figures given above are shown the relative orbits of the planets, the orbits of Mars, the Earth, Venus and Mercury (fig. 1) being drawn to a scale twenty times that of the outer ones—Neptune, Uranus, Saturn, Jupiter (fig. 2) . ”

“ Since the radiation of heat by a planet is, with our present instruments, scarcely capable of detection and measurement, the temperature of these bodies can be estimated only from general physical laws. The laws governing the radiation of heat have been so developed Temperature of the Planets.during recent years that it is now possible to state at least the general principle on which a conclusion as to the temperature of a planet may be reached. ”

“ It is not to be assumed that a molecule would move through the ether without resistance as the minutest known body does, and there is probably a radical difference between the minutest particle of meteoric matter and the molecule of a gas. ”