Look, up in the sky, it's a rare sighting

THE BALTIMORE SUN

In 1769, British explorer Capt. James Cook sailed HM Bark Endeavour around the world and into Tahiti's Mercury Bay to witness and record one of the rarest of celestial events - the Transit of Venus.

This passage of Venus, in dark silhouette, across the blazing disk of the sun has occurred only twice since Cook witnessed it. So no one alive today has ever seen it. On June 8 of 2004, billions of people from the Far East to the eastern Americas will get their chance.

It's a highlight of a stargazing calendar for 2004 that's jammed with exciting events.

Among them are a total eclipse of the moon in November (the last until 2007); a rare occultation or eclipse of Jupiter on Pearl Harbor Day; the possibility of a naked-eye comet appearing in May, a striking assortment of meteor showers and beautiful conjunctions of the moon, stars and planets.

If things go well, there will also be an unprecedented flurry of news from interplanetary spacecraft.

On Friday, NASA's Stardust probe will fly at 13,000 mph through the coma of Comet 81P Wild 2. Stardust has traveled nearly five years and 2 billion miles to reach its target.

If all goes well, it will sweep up dust samples from the comet's wispy coma and fly them back to Earth in 2006. Look for closeup pictures at http://stardust.jpl.nasa.gov

On Saturday, Spirit, the first of NASA's two golfcart-sized Mars rovers, is due to bounce down on the Red Planet. Three weeks later, its companion, Opportunity, will land.

And, on July 1, NASA's Cassini spacecraft is due to arrive in orbit around Saturn after a flight of nearly seven years. Cassini's Huygens probe is programmed to parachute to the surface of Saturn's largest moon, Titan.

If just part of this flotilla succeeds, the pictures and the science should be spectacular. Here's how the rest of the new year shapes up.

January: Venus rises higher and brighter in the west after sunset each night this month. Saturn is the steady, pale yellow "star" that rises in the east at sunset. The ringed planet is about as near and bright as it gets. The nearly full moon will rise beside it on the 6th.

Earth is at perihelion on the 4th - that mean it's at its nearest to the sun, a mere 91.4 million miles.

The latest sunrise of the year occurs on the 4th - 7:26 a.m. in Baltimore.

Watch for a striking pairing of Venus and the crescent moon, low in the west at dusk on the 24th.

February: Saturn stands directly above Orion's head, near the top of the sky in the evening. A small telescope will reveal its rings - a moving experience for first-timers.

The moon passes Saturn on the 2nd, Jupiter on the 8th, Mars on the 26th. These lunar conjunctions are good opportunities to learn where the planets are this winter.

The crescent moon makes a dramatic appearance beside Venus, in the west after sunset on the 23rd.

March: Bright Jupiter is at opposition - meaning its nearest and brightest - on the night of the 3rd/4th, rising as the sun sets. Binoculars will reveal up to four Jovian moons on either side.

Spring arrives with the Vernal Equinox at 1:49 a.m. on the 20th.

Venus is highest on the 29th, its greatest elongation from the sun until 2012. After dusk, late in March, you can see all five naked-eye planets - Mercury (if you're lucky) near the western horizon, then Venus, Mars, Saturn and Jupiter - in a queue from west to east.

April: From the 1st to the 3rd, Venus passes the Pleiades star cluster. Most people can count six or seven stars in this tight, naked-eye crowd of stars. Binoculars reveal many more. They're about 415 light years away, so the light we see left those stars around 1588. Venus nears the orange star Aldebaran on the 15th.

May: There's a chance that Comet Q4 (NEAT) will become visible to the naked eye in May. Discovered in 2001 by the Near Earth Asteroid Tracking project, it will pass within 30 million miles of Earth on May 6. Where skies are dark, look for it rising out of the western horizon after twilight by mid-month, moving higher and northward each night, headed for the Big Dipper before fading.

June: The Transit of Venus occurs on June 8. Two English astronomers were the first to observe it in 1639. It became a worldwide quest when scientists realized that, by precisely timing the event, they could calculate the diameter of Venus and the size and distance of the sun.

These transits come in pairs, and this second transit comes in 2012. But that's the last until 2117.

Never look at the sun directly, by the way - it can cause permanent blindness. Seek out a public program, TV or Webcast coverage or an experienced amateur astronomer with proper solar filters.

The entire event takes more than six hours. But on the East Coast the sun will rise with Venus in mid-transit. Baltimore will catch it from just after sunrise (5:40 a.m.) until 7:26 a.m.

The Maryland Science Center is planning safe public observations. Go to www.mdsci.org/exhibits/observatory in June for details.

The Summer Solstice arrives at 8:57 p.m. on the 20th. The year's latest sunset comes at 8:37 p.m. on the 27th.

July: Earth is at aphelion on the 5th - its farthest point from the sun at 94.5 million miles. That's 3.1 million miles farther than we were on Jan. 4.

Venus leaves the evening sky and by mid-month shines brilliantly before dawn. That leaves Jupiter outshining everything after sunset. The crescent moon approaches Jupiter on the 20th, the 35th anniversary of the first manned moon landing in 1969.

Watch for one full moon on the 1st, followed by a second, or "blue moon" on the 31st.

August: The last of the naked-eye planets are dropping into the sunset, but the evening is still rich with stars.

Look nearly directly overhead in the evening to find Vega, part of a trio of bright stars known as the Summer Triangle. Lower, toward the southeastern horizon, is Altair, 17 light years from Earth. Toward the northeastern horizon from Vega is Deneb, dazzling even at more than 2,000 light years.

The annual Perseid meteor shower peaks after midnight on the 12th. Look for as many as 90 per hour where skies are clear and dark.

September: Venus is the Morning Star. On the 1st, it's moving away from a close conjunction with Saturn - a finger's width held at arm's length.

Look for Mercury on the 10th, near the eastern horizon 45 minutes before dawn. With binoculars, Mercury can be seen close beside the star Regulus. A thin crescent moon joins them on the 13th.

The Autumnal Equinox occurs at 12:30 p.m. on the 22nd. The full Harvest Moon rises on the 28th.

October: The only total lunar eclipse visible in 2004 from the United States occurs on the 27th.

The moon enters the dark core of Earth's shadow at 9:14 p.m. The eclipse becomes total at 10:23 p.m. and lasts for 82 minutes. Enjoy it. This is the last total lunar eclipse anywhere until 2007, and the last visible in its entirety from Maryland until February 2008.

November: Rouse yourself before dawn on the 4th or 5th to see Venus (the brighter) and Jupiter in sparkling close conjunction in the eastern sky. The waning crescent moon is racing to join them, passing by Jupiter on the 9th, Venus on the 10th.

The Leonid meteor shower peaks after midnight on the 17th. Rates are declining, but should still be in the 10-50 per hour range. The moonless night will reveal more faint ones.

December: The earliest sunset is 4:43 p.m. on the 6th.

Then set the alarm on the 7th for a rare opportunity to see the waning crescent moon slide in front of Jupiter. This occultation is the first of a bright planet by a crescent moon visible here since 1976.

Binoculars will help keep Jupiter in view until it disappears behind the moon's bright, sunlit edge, or "limb" at about 3:45 a.m. About an hour later, the giant planet will pop back into view from behind the moon's dark limb.

It's a good year for the Geminid meteor shower, peaking Dec. 13. There's no moon to obscure the 120-or-so meteors expected per hour. It would be the year's best for stargazers if it weren't so darn cold. Anytime after 7 p.m.

The Winter Solstice occurs at 7:42 a.m., Dec. 21. Venus is the Christmas "star," rising in the east just before dawn.

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