"The artificiality of these canals is attested to by the fact that all canals hitherto known to us run in great circles across the surface of the planet, thus automatically achieving the shortest distance between the ends of any one canal. This alone lends considerable credence to the attestation, but the green areas at canal junctions, which are usually circular, tend to confirm it."
"My dear Dr. Bergmann," remarked Holt seriously as he put down the photograph," you must know that the project before us is a very major one. We cannot possibly base our plans upon hypotheses and guesses, no matter how plausible they may be. We can only use clear, definite facts and results of such measurement as is entirely beyond doubt.
These we must have. No effort must be spared to collect every bit of confirmed data available here. Our entire project can be endangered by a single erroneous conclusion or a set of figures which is not absolutely correct. Anything like that would distort the groundwork of our planning.
"Your dissertation was of immense interest to me and what you have said will be very useful. But I want to suggest that we drop any further attempts to line up further theories about the Martian civilization and what it may have created. It would be very kind of you to tell me something about the methods of observation and measurement that you have been using. You might also make a few suggestions about how to improve these methods, with respect to what we can do to perfect our applicable knowledge."
At this point Professor Hansen broke in. "We'll use this observatory as the main tool for all future work on Mars," he said. "I don't believe that we can use anything from the terrestrial observatories henceforward. Perhaps Dr. Bergmann will tell the Colonel why observations and measurements from here are so much better and more promising."
"I'll begin by citing an example," continued Bergmann. "Let's take the composition of the Martian atmosphere. Spectroanalysis is the only method astronomy has for finding this composition. All the light coming from a planet is reflected sunlight which has traversed the planet's atmosphere twice — once when it strikes the planet's surface, and a second time when it is reflected back into space.
"The gases of which the atmosphere is composed produce certain characteristic dark lines in the planet's spectrum. The latter is otherwise a pure solar spectrum. This happens because every gas has the characteristic of absorbing light waves of certain quite definite frequencies. We can deduce what gases are present in the planet's atmosphere from the frequencies corresponding to certain dark lines in the spectrum, know as absorption lines.
"Now, when light must pass through the Earth's atmosphere before entering a telescope, black lines originating in the Earth's atmosphere superimpose themselves upon the other black lines. Let's take carbon dioxide and water vapor, for example. They are found in the atmospheres of both Mars and Earth. Therefore those lines which are caused by the carbon dioxide on Mars are superimposed on those caused by the carbon dioxide on Earth, and the same thing applies to water vapor, since the lines lie at very definite places in the spectrum. This dilemma is circumvented by photographing Mars' spectrum at a time when the two planets are receding from or approaching one another at the highest rate. Then the Doppler Effect displaces Mars' spectrum and it is possible to distinguish Martian absorption lines from those of our atmosphere.
"Unfortunately, this procedure calls for the photographs to be made at a time when Mars is rather distant and that is an unfavorable time for observation. Results thus obtained up to now have not been altogether satisfying.
"Working from Lunetta, there are no such difficulties, and we can take spectral photographs when Mars is very close to us. Another advantage is the absence of the flickering caused by the Earth's atmosphere. From the optical angle alone, our work is vastly better than can be done on Earth.
"Now let's take another example; just think of all the difficulties confronting a terrestrial observer who is trying to follow consecutively the burgeoning and fading of any given Martian vegetative region. Of course even on Lunetta, we cannot obviate the difficulties that the change of distance between observer and observed brings during a half year. But the astronomers on Earth must fight many handicaps from which we're free.
"Many observatories in the northern hemisphere, and particularly in highly developed regions such as Europe and America, work under such poor atmospheric conditions as to be almost unsuited for delicate observation work on planets. Local weather conditions often interfere just when astronomic ones are best.
"Even observatories near the equator, less bothered by weather, work against a handicap when it comes to consecutive observations of Mars over extended periods. Let's consider an opposition of Mars. The planet is then exactly opposite the Sun, and to all terrestrial observatories, it transits the southern branch of the meridian at midnight and may be observed from nightfall until daybreak. Since Mars rotates once in 24 hours and 37 minutes, any one spot on its face appears approximately in the same place on two consecutive nights at the same moment. An observer will see the same hemisphere of Mars each night, while the other hemisphere remains invisible. The latter, however, could be seen by an observer antipodally located, whose midnight is 12 hours later than that of the first observer.
"But the picture is gradually changed by the 37 minutes difference in the times of revolution. Any given spot on Mars appears at its western rim each night later, by 37 minutes. So fifteen or twenty days afterwards, it appears just before dawn, when daylight and the low altitude of the planet obstruct observation. Therefore, to get continuity of observation, an observatory located where it can see the subject at night must take over.
"You will not find it difficult to imagine what a lot of errors can thus creep in. There's the difference in personal reactions, without even bringing up the number of unsuccessful measurements and examinations in the past stemming from lack of accurate coordination between various observatories, widely separated geographically. This may not appear insuperable, but it's very difficult to get such coordination in practice.
"On Lunetta, we have none of these handicaps. With our bi-hourly orbiting time, Mars can never be hidden from us for more than an hour. We can always see it for a full hour or more. We can keep its entire sphere in sight so consecutively that we can check changes in certain regions throughout long periods quite easily and without interruption.
This is one of the more important keys to successful examination of Mars. Being free of atmospheric disturbances, we can observe Mars even when it is most distant from the Earth, unless, indeed, it is hidden by the Sun. Such observations, naturally, lack the quality obtainable in Mars oppositions, but no terrestrial observatory can make Mars out at all at these times, for it is obscured by the bright daylight.
"There are many more advantages of a space station like this as an observatory, but I suspect it might bore you to hear them all."
"Not at all, not at all," said Holt with a friendly grin. "As an old space man, even if I was military, I always get a kick when I hear that rocketry has done something for astronomy. You know, there's a natural relationship between our two trades, and a pretty close one at that. So we've got to pull together every time we can.
"But let's get back to business. What was that you were saying about temperatures on Mars? You gave the results, but I'd like to know how you get them."
"Here's the way it's done," said Bergmann. "There's a tiny thermocouple in the focal plane of the telescope with which we're working on Mars. The strength of the radiation is a measure of the temperature of that spot on the surface to which we have adjusted the thermocouple. It's not quite as simple as it sounds, for the total radiation of a planet consists of rather more than the heat radiated by the planet itself. The "more" is reflected solar radiation, and our conclusions must be drawn from the former only. So we've got to separate the two. This is done by interposing a layer of water about half an inch thick in the ray. This permits the short wave, reflected solar radiation to pass, slightly weakened. But it completely cuts off the long wave heat radiation which comes from the surface of the planet. There's a ratio between the current produced by the thermocouple with and without the water filter and this ratio enables us to determine the rate of the planetary radiation. With it, we can finally derive the temperature at the surface.