Just look at those planets move across the sky! Sometimes, if you watch closely, they dosey doe around in a nice loop and start going backwards!

Just look at those planets move across the sky. Sometimes, if you watch closely, they do si do around in a nice loop and start going backward.

They really do appear to make this motion, but you have to watch carefully. Their “zip” across the heavens seems to be more of a snail's pace because they are so far away. You have to look night to night and patiently note their positions relative to the stars in the background.

Only the outer planets do loops, by the way: Mars, Jupiter, Saturn, Uranus and Neptune, and the so-called “dwarf planets” (there are more than seven, in case you were asking), such as Pluto. The inner planets -- those between Earth and the sun (Venus an Mercury) -- refrain from somersaults.

This strange looping motion is called “retrograde.” One could also say, “renegade” for this strange behavior. The reason the outer planets loop back is simply because the Earth, which is moving faster, overtakes the outer planet and passes it by. As we pass Mars, for instance, it seems to loop backward against the stars (east to west), and then starts to resume its normal direction (west to east).

Retrograde loops had the ancient thinkers befuddled, when Earth was considered the center of the universe and everything went around us.

Whenever a galaxy or a planetary system forms from its dust cloud, most of the material will rotate in the same direction. The collapsing of the cloud starts the motion and is kept up by angular momentum. Our solar system’s planets move counter-clockwise as seen above the north pole of the sun. (Yes, the sun has a north pole and south pole, but be assured, neither zone is frigid.)

Retrograde motion is observed as the outer planet reaches “opposition,” the point where it is opposite in the sky from the sun and thus rises at about the same time as the sun is setting. The farther out the planet, the smaller is the apparent loop it makes.

While we’re at it, six of the eight main planets behave by rotating counter-clockwise as well. Having to be different are Venus and Uranus. They are spinning the “wrong way” because they are so far tilted over that as seen from the same reference point (above the sun’s north pole), they appear to be spinning clockwise.

The next clear evening this May, look well up in the southern sky for the bright planets Mars and Saturn. The reddish planet Mars is most easily noticed due to its color -- it is on the right. Far to the left is yellowish-white Saturn. Between these is a bright bluish-white star, Regulus, the brightest star of the constellation Leo the Lion. Both Mars and Saturn are currently of similar magnitude, +0.8. By contrast, Regulus shines at magnitude +1.35, or a little fainter than these planets (the higher the magnitude number, the fainter).

Note that Regulus is about 77-1/2 light years away or 449.5 trillion miles. These planets, which reflect the light of a much closer star, our sun, are far nearer. Mars is close to 34 million miles from us, and Saturn is around 497 million miles away -- not as far as it used to be before our modern planetary spacecraft!

Venus is much more brilliant (magnitude -3.9), visible in the west-northwest during twilight.

New moon is on May 13.

Peter Becker writes for the Wayne Independent in Honesdale, Pa. Contact him at pbecker@wayneindependent.com.