PHILADELPHIA - Between homework, all new episodes of the "Gilmore Girls" and the Sixers effort to end their NBA playoff run with some dignity, chances seemed slim last week for interesting our preteens in skywatching.

After a few "humphs" and some amazingly slow shoe tying, we were on our way.

A nearly full Moon, midway up in the eastern sky, followed us out Ridge Avenue, which by name presumed to offer high ground and a good view of the horizon, where the action would be. Venus beckoned already, higher than I'd expected, a "star" that shines vividly even before the lights on the grand stage are fully dimmed.

The radio told us the Sixers were losing, but it was early in the game and we had hope. And, I was reminded, my sky show had formidable competition.

The evening darkened. Jupiter appeared, hovering so high as to appear uninterested in the main planetary grouping. I pointed it out with one eye on the road, picked a side street at random and turned left. One more block brought us to an empty, muddy field that fell away toward a school along the south edge and some squat, two-story rowhouses to the west. A few budding trees and some power lines would obscure the planets just before they set, but overall we'd stumbled onto a grand viewing location with little effort.

Connecting the dots

The horizon was giving up its last orange hues. Overhead, deep blue turned to a washed out purple. I shut the car off, rolled down the window and started pointing.

"Draw a line between Jupiter and Venus," I explained, "and somewhere in there you'll see Saturn, soon as it gets a little darker." The kids maneuvered with surprising vigor for window seats. Perhaps skywatching has a bit more allure when those Gilmore Girls aren't around. I turned the radio down to further my advantage.

"I see it!" one of the kids exclaimed. A sighting. Our expedition had now become less like science and more like fishing. They were hooked.

"Now follow the same line down past Venus," I continued, "toward the trees, and pretty soon you should be able to see Mercury." A few moments later this most elusive of planets twinkled into view. The sky darkened further and finally, with effort, we found Mars, relatively dim nowadays as it is far from Earth.

All the while, the kids didn't complain. They were as captivated as I could hope, and now we could explore the solar system's movements, right here from this muddy lot surrounded by bright streetlights smack in the middle of America's 5th largest city with absolutely no special equipment.

And we didn't even have to get out of the car.

The questions

The first question, with a little coaxing, came from one of the kids.

"Why are they all in a line?"

I explained that the planets all follow basically the same path across our sky, from east to west, because they all reside in roughly the same imaginary plane in space. It is the plane through which they travel as they orbit the Sun and a plane they share with Earth. I noted with satisfaction that preteen eyes did not roll back into preteen heads, thanks I think to the simple fact that our textbook was the deepening night.

I asked the next question: "Where did the Sun set?"

Kids, and even many adults, don't know this intuitively anymore. Heads swiveled to check each window. Then twilight dawned on them and they both pointed west, toward the fading, colorless glow. I pointed out that they were pointing at a spot that was also along the line formed by the planets.

Now watch, I said, while we sit here, as Mercury sets just like the Sun. All the planets, in fact, rise toward the east and set toward the west. So do the stars (some, around the North Star, just sit up there and go in circles, but I left that fact out).

Why do they all set in the west?

"Because the Earth spins," the kids said together. Exactly. The same motion that generates night and day and guides the Sun across our sky also controls the movement of the stars and planets across our field of view at night. Synapses were making lifelong connections, I hoped.

I closed the window, turned the radio up, and we headed home before the sky had a chance to lose its advantage.

The kids don't know it yet, but I'll be coaxing them out at least twice more as the planets move ever closer to the most thrilling configuration, a tight triangle that will form May 5-6. And as I know now, making the planet gathering a family gathering won't be as hard as I once thought.

What to look for

As the Great Planet Alignment of 2002 approaches its climax, here are some things to do and discuss:

Each night, notice how the planets draw closer together. Here's why: The inner planets move around the Sun much more quickly, effectively lapping the lumbering outer planets. From time to time, as now, a few of them are in roughly the same line of sight from our vantage point. To envision this, imagine flying up above the solar system and looking down on it. Right now, you'd see Earth and the five visible planets all more or less lined up on the left side of the Sun.

Stretch your arm out, make a fist, and see how many planets you can block out at once. Your fist in this configuration covers about 10 degrees of sky, so even if you don't know or care what degrees are (astronomers use them to measure distances and sizes of objects in the sky) you're employing some technical astronomy to your observations. On May 5 and 6, your fist will blot out Mercury, Venus, Saturn and Mars!

Draw or print a sky map. Even a quick sketch of the planet's positions, based on one of our online maps [here's one], will help you identify them more easily once you're outside. Our award-winning Starry Night software, installed on your home computer, can provide you with personalized maps of the sky exactly as seen from your location. On Friday, May 3, we'll provide printable sky maps for three nights next week during the climax of the whole event.

Enhance your experience with binoculars or a small telescope. Look for Saturn's rings, an amazing sight for any first-timer and one that even experienced astronomers come back to over and over. You should also be able to see up to four points of light near Jupiter, strung out in a line. These are the Galilean Moons: Io, Europa, Ganymede and Callisto. They're named after the guy who used one of the first telescopes to find them in 1610. Also, Mercury goes through phases, just like the Moon. The planet is waning now, and you can watch it happen.

Go out early, then watch the planets set. Depending on your view of the horizon, Mercury can be gone just an hour or two after sunset. If one of the planets gets near a reference point -- a tree, power line or even the rearview mirror of your car, note its location and close your eyes for 10 full seconds. Open your eyes and see how the planet has moved. It's direction of movement will be slanted along the line that the planets form in the sky, a line that points to where the Sun had earlier gone down.

More information:

Mercury Joins the Show
Columnist Joe Rao's weekly tour of the sky focuses on the planet alignment in this April 26 installment.

The Science of the Alignment
How it works, and what to expect through early May.

Main Spacewatch Page
More details about this and other skywatching opportunities.