Planets align for heavenly treat

March 26, 2004|By Frank D. Roylance | Frank D. Roylance,SUN STAFF

We're all pressed for time. So, if you've ever wanted to go outside and see a real planet with your own eyes, do it now and get five for the price of one. Six if you count Earth.

For a limited time only, Mercury, Venus, Mars, Jupiter and Saturn - every planet in our solar system that can be seen without visual aids - will be splayed out across the evening sky.

"A lot of times people have a lot of difficulty picking out all the planets because they are so starlike," said Jim O'Leary, director of the Maryland Science Center's Davis Planetarium. "Here, we're looking at all our planetary neighborhood spread out in front of us in the sky."

Although Mercury will sink into the glare of sunset by April 5, the other four planets will remain visible for about two more months.

Similar groupings occur from time to time when the "naked-eye" planets and Earth, moving around the sun in their individual orbits, happen to bunch up on the same side of the solar system.

A much-publicized assembly of the same spheres in May 2002 was said to be the best since 1940, and the tightest grouping until 2040.

But astronomers say this year's family reunion may be the best evening opportunity of its kind for decades to come. And the show has begun.

Venus has been blazing high in the western sky for months, gleaming like an aircraft landing light throughout the evening. You can't possibly miss it.

The second planet from the sun, Venus is just 70 million miles away, and so brilliant right now you can see it in the daytime if you know where to look.

Giant Jupiter is 420 million miles away - six times farther than Venus. But it, too, is a snap to spot, rising in the southeast, on the opposite side of the evening sky from Venus. While not quite as gaudy as Venus, it is still easily the brightest object in that part of the sky.

"We get a lot of questions about those two - Venus and Jupiter," O'Leary said. Callers ask, "What are those things? They can't be stars. They can't be planets."

NASA's orbiting Galileo spacecraft photographed and studied Jupiter and its largest moons at close range for eight years before controllers ended the mission in September by plunging the probe into the Jovian atmosphere.

Saturn is dimmer, and a bit trickier to locate. Look for it almost directly overhead in the early evening hours. It doesn't stand out much from surrounding stars, but you can find it by "star-hopping" from the constellation Orion."

Start at Orion's belt - three stars in a tight row about halfway up from the southwestern horizon. The brightest star just above the belt stars is the red giant Betelgeuse. Now hop about the same distance higher in the sky, and that pale, yellowish "star" just south of the zenith (directly overhead) is Saturn.

NASA's Cassini spacecraft, carrying an international cargo of instruments, is in its final approach to the ringed planet. It is expected to begin orbiting in July, and will send a probe to the surface of Titan, Saturn's largest moon, next winter (see http://saturn.jpl.nasa.gov).

Mars and Mercury are the hardest to spot.

Mars is that small, amber dot just above and to the left of Venus, separated from it by about the width of your fist held at arm's length.

It's a feeble glimmer compared with Mars' brilliant appearance in August, when the Earth made its closest approach to the Red Planet in all of recorded history. The Earth was just 35 million miles from Mars at the time. We've raced ahead since then, leaving Mars 175 million miles behind.

Despite the expanding gulf, NASA's Mars rovers Spirit and Opportunity continue to send back photos and scientific data from the Martian surface (see http://marsrovers.jpl. nasa.gov).

Mercury is the closest planet to the sun, and almost always lost in the sun's glare. It does make regular appearances at the extremes of its orbit, either low in the eastern sky before sunrise, or low in the west at sunset. But it's always a coup for stargazers who spot it.

This week and next, look for Mercury low in the west in the hour after sunset. If skies near the western horizon are clear enough, Mercury will pop out of the deepening twilight as a faint but steady white "star."

Mercury, now 90 million miles away, hasn't been visited by a spacecraft from Earth since Mariner 10 flew by in 1975. But NASA is preparing for a launch this summer of the Messenger mission, built and managed by the Johns Hopkins Applied Physics Lab in Howard County. If all goes well, the spacecraft should begin orbiting the planet in 2011 (see http://messenger. jhuapl.edu).

As an added bonus, a crescent moon has been climbing among the planets in the west since Monday. It will return to the evening sky April 22 and 23, although Mercury will be gone by then.

One of the most striking things about these gatherings of planets is the way they line up in a nearly straight line across the sky. It's no accident, O'Leary said. Like peas arrayed across a dinner plate, "it's an indication of the flat plane our solar system is constructed in."

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