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Curt Nason

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The space missions and giant telescopes of the past few decades have yielded a great deal of knowledge about our neighbouring planets; sadly, at the expense of the mystery and romance that sparked our youthful minds. This week presents a chance to glimpse them together in the night sky and perhaps visit them in a flight of fancy.

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Mercury, Venus, Earth and Mars comprise the inner or terrestrial planets. They have a higher proportion of heavy, rocky material than the distant, giant gas planets, the nearest of which is three times farther from the sun than Mars. When the sun formed 4.6 billion years ago it was surrounded by a disc of gas, dust and solid clumps. Radiation streaming from the sun dispersed the lighter gases a greater distance, leaving the clumps to build up the inner planets through collisions. Although the gas giants also have rocky cores, most of their mass is from the lighter atoms and they are three to four times less dense overall.

This week provides an opportunity to see all four terrestrial planets simultaneously, but you will need binoculars, a clear view of the western horizon, and a little luck with the weather. Take note of where the sun is setting, then after 10 minutes scan above the horizon to the left of the sunset point. It might help to focus your binoculars first on a very distant object. You should be able to pick out Venus in the bright twilight. Having located it, readjust the focus so that Venus is a small point of light. Now, try to see Venus without the binoculars; it is surprisingly easy when you know where to look.

Mercury and Mars should pop into binocular view within half an hour of sunset. Placing Venus inside of the 2 o'clock position in your binoculars, Mercury will appear near the 8 o'clock position and Mars at 11 o'clock. Both will be dim points of light and will set before the sky gets dark, but if you also have the horizon or a tree in view then you are seeing all four terrestrial plants at once. By Thursday, Venus will have moved to just above Mars, offering an intriguing view in a telescope. Mercury, Venus and Mars form such close groupings about six times a century, on average, but sometimes they are too near the sun to be observed. The last visible binocular grouping was in 1976.

If you have difficulty finding the trio of planets and if you really want to, hop a plane to the southern hemisphere where they appear higher in the sky. The line of planets makes a shallow angle with the horizon during our autumn evenings; therefore, they are hidden easily by trees and buildings. The opposite occurs in the south, or in the northern hemisphere in spring. This shallow angle is the reason we see the autumn full moon prominently over several days, giving us the Harvest Moon in September and the Hunter's Moon in October.

The science fiction tales of the last century were rife with imaginative settings on the terrestrial planets. Mercury had lanky humanoids with eternal thirst; Venus with tropical swamplands hosting dinosaurs and, of course, beautiful maidens; and industrious critters tended the canals of Mars. By the 1980s space probes had shown Mercury and Mars to be arid rock, and Venus is hell with its 470 C temperatures and clouds of sulphuric acid.

Recent space probe findings have renewed our hopes of discovering alien life. Water ice has been uncovered on Mars, opening a slim possibility of ancient civilization or at least a hockey team.

The Saint John Astronomy Club meets on the first Saturday of the month. Contact Curt Nason (648-9063, nasonc@nbnet.nb.ca) or visit their website at http://sjacnb.tripod.com.