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Mars Approaches

Throughout 2000 Mars was conspicuous by its absence from the evening sky. This year Mars begins a lengthy stay in our evening sky coming nearest to us in June. Mars will be nearer than usual as we pass it this year, a fore runner of 2003 when Mars makes it closest approach to Earth until 2629. Every other year Mars reaches the outermost part of its orbit close to the time that Earth makes its closest approach to the Sun. The situation reverses itself every two Summers when Mars is closest to the Sun just as Earth is at its most distant. The closest summer approaches are about 34.4 million miles while the most distant winter passes are more than 63 million miles. At a close approach Mars appears to be more than 3.3 times the area of Mars at a distant approach.

Until the advent of spacecraft, close oppositions of Mars were highly prized by astronomers. At close approaches surface details begin are visible that cannot be seen at any other time. Mountainous areas, lowland plains and polar caps are easily seen in large telescopes. However, you need to be careful when you study the red planet. No other planet has led to more incorrect sightings than Mars. The "canalli" [channels] of Schiaparelli became the canals [with hints of intelligent life] of later astronomers. With superb close-up photographs from spacecraft we now know that these lines were tricks of the human eye that wants to see boundaries between various shades of color.

Relying on photography to resolve the images has also been a problem. With film, longer exposures are required of dim objects like Mars. However, long photographs suffer from blurring caused by the Earth's atmosphere, vibrations in the camera, and over exposure of bright areas while darker areas are under exposed. Sometimes, the human eye catches details that the camera misses because the eye sees at a moment of perfect seeing while the camera combines both good and bad seeing in a single image.

Today, a new type of camera, called a CCD (Charged Couple Display) has all but replaced film as the media for astronomical photography. It combines some of the best features of both the human eye and film. It can take many short exposures, waiting for moments of finest seeing while also collecting over long periods so that dim objects can be perceived. At Frosty Drew Observatory we will be training our CCD on Mars this late spring and early summer to gain practice for 2003 when we will hope to really have excellent pictures of Mars.

It would be nice if I could truthfully say that CCDs are all gain and no loss, but this is not the case. CCDs are sensitive not only to visual light photons but to infrared photos as well. Things that are warm (like people and room temperature equipment) emit infrared photons vigorously. To allow CCDs to work, they must be chilled. [Ours has a built in refrigeration unit].

Color photography is possible, but only by taking several images through four filters (blue, green, red and infrared). Once a CCD has finished taking an image (literally counting the photons at each pixel), a complex process is required to convert the image to something we can recognize. Pixels with too many photons must be "scaled down" while pixels with some but not many photons must be "scaled up". There are no convenient film finishing stores that can do this for you with CCD images. Each of us must become skilled image finishers before we can show off a prized view of Syrtis Major or the polar caps. Still and all, I can hardly wait until I see our first full color views of the red planet this summer as we practice for 2003.

While we wait for Mars to arrive in the evening skies later this spring, why not stop over at Frosty Drew Observatory to see Venus, Saturn or Jupiter as they dominate the western sky? Just remember to dress twice as warmly as you would on a normal evening. Half a century of viewing the skies has convinced me of one thing: a cold windy night in an observatory dome will chill even the most cold tolerant person.

Leslie Coleman
Author:
Leslie Coleman
Entry Date:
Jan 1, 2001
Published Under:
Leslie Coleman's Columns
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