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Mercury, Venus and Saturn to appear in rare grouping

WASHINGTON—Worlds won't collide in the next few days, but they'll get pretty close in the eyes of the casual observer.

Starting Friday night, Mercury, Venus and Saturn will appear to be so close together that the bright trio will look like a new constellation. The rare grouping, which can be viewed through Sunday night, will be followed Monday night with Mercury and Venus separated by such a small distance that some observers may mistake the two planets for one large star.

The planets won't be in any danger of a galactic collision. They'll still be millions of miles away from one another, but from Earth they'll look as if they're side by side.

The Monday night separation of Mercury and Venus by one-tenth of one degree—or one-third of the visible surface of a full moon—isn't expected to happen again until 2070.

"They'll be pretty darn close," said Geoff Chester, an astronomer at the U.S. Naval Observatory in Washington.

The appearance of three planets so seemingly close to one another is less rare and can be seen every five to 10 years, Chester said. Mercury, Venus and Saturn will appear to be within three full moons of each other this weekend.

The trio doesn't mark a transforming celestial occurrence, but rather the coincidence of the planets' different orbits, scientists said.

"Having the planets visible at the same time is quite a sight, but ... it happens, no big deal," said Allan Treiman, a senior staff scientist at the Lunar and Planetary Institute in Houston.

Though they aren't scientifically significant, the planetary maneuverings are an easy way for people to become re-engaged in star-watching because the planets can be seen without instruments, said Jack Horkheimer, the host of "Jack Horkheimer: Star Gazer," a Miami-based weekly PBS show. He said Americans, especially those in cities, had trouble star-gazing because streetlights obscured most of what could be seen at night.

"These are the kinds of things that have deeply impressed the minds of our ancestors for thousands of years," he said of the planets' close proximity. "It's wonderful to be able to connect with your ancestors, to see what your ancestors saw."

The best time to view the phenomenon is 30 to 45 minutes after sunset (set to take place at about 8:30 p.m. EDT). Observers will find the planets in the western sky. Streetlights shouldn't block them out, Horkheimer said, because they probably won't be on yet.

Venus, which will be sandwiched between Mercury and Saturn, will give off a very bright light. Mercury, to Venus' right, will give off a pinkish hue. Saturn will be to the left of Venus and will look white. Horkheimer recommended using binoculars or telescopes to see some of the planets' striking details, such as Saturn's rings.

Being able to see Mercury clearly is eventful in itself, Chester said, because the planet closest to the sun is rarely seen in a dark sky. He noted that the 16th-century astronomer Nicolaus Copernicus, who theorized correctly that the sun was the center of the solar system, never saw Mercury.

"You have an opportunity to make an observation, albeit a casual one, that was missed by one of the world's great thinkers," Chester said. "For me, that's worth a few minutes of time from my everyday life."

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For more information online, go to www.jackstargazer.com, http://science.nasa.gov/Astronomy.htm or www.aaa.org.

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(c) 2005, Knight Ridder/Tribune Information Services.

GRAPHIC (from KRT Graphics, 202-383-6064): 20050613 Planets meet

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