Through telescopes on either orb, an observer can easily and clearly study the other without the surrounding atmosphere acting as an interference.
Astronomers on Earth have given the heavy atmosphere surrounding Venus as the reason that planet's markings have never been seen with even the finest telescopes. In this line of reasoning, the markings on Earth should be obscured by her heavy atmospheric belt. But they are not.
Taking all known facts into consideration, planets Mars, Jupiter, and Saturn must have atmosphere very similar to the Earth or the Moon, or maybe somewhat between these two, since from the Earth definite markings around and on these other planets are so plainly visible. Even through five hundred miles of atmosphere, with some of it as dense as it is close to the surface of the Earth, people there can easily see planets and other heavenly bodies with their naked eyes although markings cannot be observed without the aid of a telescope.
It has been said that if atmosphere surrounded the Moon and other planets, clouds would be seen from time to time floating above them, such as we see over the Earth when on the Earth. We have been watching for cloud formations around the Earth as we have been sitting here noting every little detail and discussing our observations. But we haven't seen any. Yet we know from experience that somewhere over the Earth there are clouds moving. At the same time we realize that a cloud large enough to cover the entire state of California would scarcely be visible even from here and certainly not from the great distance between other planets and the Earth. Earth observers have however noted dark patches on these planets which were not always there the next time they looked. These may have been cloud shadows.
On the other hand, since the Earth is visible from the Moon and the Moon and other planets, with the exception of Venus, are visible from the Earth, then all these must have a rarefied atmosphere in comparison to that surrounding Venus, yet similar to each other.
Continuing in this line of thought, there is an atmospheric condensation that takes place over different parts of the Earth from time to time which is impenetrable even with our finest telescopes. This we call 'fog'. Should a dense fog enfold the entire Earth at one time, she probably would be hidden from the view of other planets, unless they had telescopes better than those on Earth which would penetrate such denseness.
This must be the type of atmosphere constantly around Venus. If so, people on that planet would be unable to view the heavens as we do unless they have more penetrating eyes than we have. Also their scientists and astronomers must have finer instruments than we have on Earth to be able to study the vastness of the universe as our scientists are able to delve into it with the aid of their instruments.
"Wonder if I can find anything in the sky from here that I've never heard of on Earth," mused George as he played around with the telescope.
"Hey, Doc, what's this?" he suddenly exclaimed.
"Looks like a moon to me," remarked Dr. Johnston as he looked intently into the telescope. "Could be a moon to this one yet never be seen from Earth. I've heard of a dark moon to the Earth, but of course no one there has ever seen it. This must be it."