View three planets April 17

Published 3:08 pm Friday, April 16, 2010

Three of our solar systems five naked-eye planets, Venus, Mars and Saturn, will be on display after sunset on Saturday, April 17.

In appearance, the three planets are very different from each other, and since they can all be seen at one time these differences can easily be discerned, even by a casual observer.

Venus is by far the brightest of the three outshining the brightest star in the sky, Sirius, by a factor of exactly ten. By a lucky coincidence, Sirius will be located about 30 degrees south of Venus for comparison. Seeing Venus and Sirius together will allow you to see what ten times brighter really means in terms of the sense of sight.

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But Mars and Saturn are no slouches with respect to brightness only 12 stars rival them, all the rest a dimmer. And since all the planets reside in the same plane (the path of the sun) it is easy to avoid confusing them with bright stars.

With respect to color, Venus is pure white, Mars is slightly orange, and Saturn has a yellowish aspect. Through a telescope Venus shows no surface detail as it is enshrouded with a permanent cloud cover which reflects the white light of the sun. Mars on the other hand has a very tenuous and transparent atmosphere, and its rust color reflects exactly that rust (iron oxide) on its surface. Saturns high altitude cirrus methane ice clouds account for its slightly yellowish appearance.

Of these three planets, only Mars is a possible target for human explorers. Venus is far too hot its surface temperature would melt lead. And as for Saturn, it has not surface in the conventional sense. Saturn is a world composed, like the sun, primarily of hydrogen gas. There is no place to land on Saturn.

The most spectacular visual feature of Saturn is its system of rings which span a distance of 170,000 miles, more than 20 times the diameter of the earth. The rings are highly reflective and account for half the planets brightness. The rings are thought to be the shattered remains of a moon that ventured too close to Saturn and was broken up by the tidal forces of its massive gravity.

To add further interest to Saturday nights celestial show, a three-day old crescent moon will be in the vicinity of Venus in the constellation Taurus, the bull. Earthshine (sunlight reflected from the earth back to the moon) will softly illuminate the dark part of the moon making for very lovely and interesting sight that you may not have noticed before.

If the sky is clear, we hope you will join the local astronomers (who are always armed with telescopes) at FENCE after sunset this Saturday night.

Park at the main building and walk up to the top of the hill. And dont forget to bring your binoculars!