AN ASTRONOMER PRESENTS THE HEAVENLY OUTLOOK

Evening Post, Volume CXIX, Issue 128, 1 June 1935, Page 25

AN ASTRONOMER PRESENTS THE HEAVENLY OUTLOOK

A glimpse of the earth as it should appear to a man on Mars was pictured before the closing session of the annual meeting of the American Philosophical Society at Philadelphia. Dr. Vesto M. Slipher, director of the Lowell Observatory at Flagstaff, Arizona, under whose direction the planet Pluto was discovered and who was the first to determine definitely that the atmospheres of the giant planets were composed of "coal damp," presented the Martian "outlook," says the "Daily Express." ' He showed the scientists how man on earth can build for himself a "ladder of light" upon which he can climb to Mars and look at our own little planet from afar, as it twinkles on the Martian night sky. The vision of the earth from Mars was not mere guesswork, but-was based on a careful analysis and comparison of the lights and shadows cast by the earth on the surface of the ■moon. With these light beams as building material, the "portrait" of the earth as viewed from Mars was painted in striking colours. Here is our planet as the Martian would see us, in the word picture painted by Dr. Slipher: "Consider how the earth would appear from, say, 50,000,000 miles or more. We observe it and compare it with Venus or Mars. "What shall we see? Not very much at first. Only prolonged observation will yield a working knowledge of the planet. "Earth would appear larger, and brighter than Mars and bluer even than Venus. Its polar caps could be made out much less easily than those of Mars.

"Seasonal changes would in time become recognisable in other features than polar caps. The oceans and wooded areas would be nearly black, as seen through holes in the clouded atmosphere, but veiled with blue. "Oceans of the earth and green vegetation might not always be easily differentiated. Under best observations the Nile Valley would show seasonal changes not very different from a strong canal on Mars. "The Sahara and Arabian Deserts would be one-third the brightness of the clouded areas. Large vegetated areas of earth would appear seasonally not very unlike the extended dark areas of Mars. The clouds would be earth's brightest feature. "Certainly. no evidence of man's doings would be .recognisable. Our own planet would, appear very intriguing, far more promising than Venus, but not easily observable as is Mars from earth." Though we cannot observe the ■earth's features from without, Dr. Slipher explained, it has been possible so to examine its integrated light by analysing the "earth light," or "earth shine," reflected from the dark.side of the moon. The light of the crescent moon is much stronger in the yellow and red parts of the spectrum than is the earth light, whereas at the violet end of the spectrum the two are fairly equal. This shows, it was explained, that the 'earth shine is relatively stronger in the blue and violet, and that therefore the earth is a bluish planet. Telluric absorption of water and oxygen have also been found to be accentuated in earth's"portrait." .