Sky Watch: A planetary promenade

If you've been putting off stargazing until something really cool happens in the heavens, this is definitely your week! Three planets will be dancing beautifully in the western sky over the next two weeks. And the best part of the story is that you won't need to leave the brightness of the city, nor will you need to stay out late, to enjoy the show.

At dusk this week, the brightest planet, Venus, and the second-brightest, Jupiter, will seem to be drifting toward each other from night to night, creating a series of stunning patterns.

Jupiter, of course, is the largest of all solar system planets, 11 times larger than our own Earth. It appears so bright in the night sky because its huge orb is composed of highly reflective clouds. And speaking of highly reflective clouds, Venus -- though only the size of our Earth -- is also shrouded by clouds, which reflect about two-thirds of all sunlight back into space. These two worlds alone will make the sky show worth seeing.

Joining the party will also be the innermost world of our solar system, Mercury, which can only be seen for a few weeks per year. Mercury is the nearest planet to the sun and, as such, whips around its orbit once every 88 Earth-days at a distance of "only" 36 million miles from the scorching face of our star. From our terrestrial vantage point, Mercury appears so close to the sun that it's often lost in its glare.

In fact, this planet's elusiveness is legendary; it's been said that the great 16th century Polish astronomer Nicolaus Copernicus -- who overturned the long-held notion that the Earth occupied the center of our planetary family -- had never actually seen this world with his own eyes. Now I can't say whether this is true, but it certainly makes sense given what we know about weather conditions in Eastern Europe and how buried in the glow of twilight Mercury always remains.

Keep an eye on these three worlds this coming week and the week of May 26 through June 1 because each night their relative positions will change. This is caused by their own motions around the sun, coupled with those of the Earth itself.

Of course, I hope you'll watch the entire show every night, but if you have to choose just one night to check it out, that night should be Sunday, May 26. At dusk on that day, the trio will appear in its most compact arrangement. In fact, if you have binoculars, you'll be able to see all three in the same field of view. And if you wait until they get a bit lower and the horizon enters the field of view, you'll see a fourth planet as well -- the Earth!

Their apparent proximity, of course, is purely an illusion caused by these worlds lying roughly along the same line of sight. On May 26, for example, Jupiter lies on the opposite side of the sun -- 564 million miles from Earth -- nearly as far as it ever goes. Venus, on the other hand, lies 153 million miles, and Mercury only 106 million miles from Earth.