Jupiter and Saturn have finally lumbered around. Those lazy bodies of rock and gas, it takes them forever to orbit. They have finally rendezvoused with the rest of the party -- Mars, Venus and Mercury -- and now all five planets visible with the naked eye can be seen on the western horizon.

They're line-dancing, mingling and conjuncting, in a diagonal slash across the sky that earthlings have not seen since 1940 and will not see again until 2040. While this arrangement happens every 20 years or so, it sometimes appears during daytime, making it harder to see, and it is rarely as vivid.

The planetary phenomenon happens to coincide with National Sky Awareness Week, as hundreds of professionals and amateurs around the world begin hauling out telescopes and trekking to parks and open spaces to take a peek at the luminous confluence.

The gazing technically began Saturday, but the weather here has not been cooperative. Not to worry: The show lasts until May 15. The best viewing time is 8:20 p.m., twilight, when the sun has dipped below the horizon enough that it does not overwhelm the glow of planets but still illuminates their hues of blue, yellow and orange.

"This will be something that spawns a new crop of astronomers. It's like when astronomers say, 'Oh yeah, it was that beautiful moon and Venus conjunction back in October '82, I'll always remember it.' Or, it might have been the comet Haley or the comet Hale-Bopp. Well, there will be people who will always remember this," said Alan MacRobert, a senior editor at Boston-based Sky & Telescope magazine. (This month's cover line: "MICROQUASARS in the MILKY WAY.")

Area astronomers have organized public events at several parks in the District, Alexandria and Haymarket.

Astronomy teachers in the Fairfax County school system expect about 400 people at a workshop Sunday at Huntley Meadows Park. And National Capital Astronomers, one of the oldest stargazing clubs in Washington and Rockville, will be in Rock Creek Park at Military and Glover roads NW on May 11.

Not everyone is enthralled, however. Some die-hard astronomers contend that the lineup is unusual but no big deal, scientifically.

"There's nothing you can learn by looking at it," said Bob Bolster, a founder of the Hopewell Observatory in the Bull Run Mountains near Haymarket and a member of National Capital Astronomers. "It's not going to produce any data. It's not really a big deal for the serious people."

The configuration is not as fascinating as the sky's lesser-known and less ostentatious phenomena, said Ed Karch, president of the Northern Virginia Club of Astronomers. "Most of the serious observers are looking for star clusters, galaxies and nebulas -- glowing spots that could have been stars that exploded after getting too dense."

Nebulas, he added, are cool.

But some observers are riveted by the lineup's peculiarities, especially Mercury, the closest planet to the sun.

"Mercury is always a trickster. It's always a personal triumph if you get a peek at it because it sits so low on the horizon," said John Avellone, 61, a Northern Virginia Astronomy Club trustee. "But when you look at the whole thing, you just say, 'Gee, these are the gears of the clock -- the sky clock.' "

All of this is not to say that planetary matters are the exclusive province of astronomers. Astrologers are busy portending the future based on the alignment's relationships to the constellation Gemini and the planet Pluto.

Evil Pluto, that is.

"It's not the alignments we have to be worried about," said Bob Marks of New York, a member of the National Council for Geocosmic Research, who runs a 300-plus-page Web site on astrology. "It's that they are facing opposite of Pluto, and when that happens you get upheaval. Look at what's happening in the Middle East. It's the killer. Planets aligned in 1962 and we had the whole '60s revolution, the Vietnam War and . . . "

And?

"Jennifer Jason Leigh, the actress, was born -- the day after a major eclipse. She's out there. She's a super Aquarian -- Aquarians are all crazy, and they'll be the first to tell you that. Actually, they're all geniuses."