May 24, 2002

A Dazzling Duo

Dazzling Duo

This week brilliant Venus and giant Jupiter are rushing toward a close encounter in the western sky.


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May 24, 2002: Stick out your index finger and hold it at arm's length. The width of your fingertip (less than 2 degrees wide) is how far apart Jupiter and Venus will be on June 3rd -- a remarkable close encounter between the two brightest planets.

There's no need to wait until June, however. Even now Jupiter and Venus are eye-catching. They pop out of the evening twilight long before the sky grows completely dark. Brilliant Venus appears first, not far above the western horizon. Dimmer (but still bright) Jupiter emerges next, higher in the sky.

The two planets are rushing together, drawing noticeably closer each night. In fact, there is no danger of a true collision -- Jupiter is 560 million miles from Earth while Venus is only 120 million miles away. The two will converge in appearance only.

But what an appearance it will be!

Right: Canadian sky watcher Lauri Kangas captured this image of Venus and Jupiter emerging from the evening twilight on May 20, 2002. Venus appears twice: in the sky and reflected from the lake.


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Close encounters between Jupiter and Venus happen often enough, every year or so. Some, though, are better than others. For instance, on June 17, 2 B.C., the pair drew so near -- just 6 arcseconds (0.002 deg.) apart -- that they merged into a single dazzling point of light. Some scholars believe that was the Star of Bethlehem mentioned in the Bible.

The coming encounter won't make that kind of history, but it will be pleasing to sky watchers. The pair will turn heads even in urban areas where city lights often obliterate astronomical events. Venus is so bright that it's often mistaken for a landing airplane or a UFO. Sky watchers in remote dark areas say that the planet can cast pale shadows. Amazing.

Venus is bright because the planet is covered by sunlight-reflecting clouds (made of carbon dioxide and sulfuric acid). Jupiter is cloud-covered, too, and 11 times wider than Venus. Jupiter's clouds (made of ammonia ice, water and sulfur compounds) are somewhat less reflective than Venus' clouds -- but that's not why Jupiter seems dimmer. The real reason is distance. Jupiter lies seven times farther from the Sun than Venus does.

If the two planets shared the same orbit -- Venus', say -- Jupiter would outshine Venus by a factor of 100. The giant planet would beam down on Earth like a bright Moon. Lovers would take Jupiterlight strolls and composers would write the Jupiterlight Sonata. (Fortunately Jupiter is far away. Otherwise its powerful gravity would wreak havoc on Earth's orbit.)

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Above: The western sky shortly after sunset on June 3, 2002, viewed from mid-northern latitudes.

Only two weeks ago, observers of the western sky could spot five planets after sunset: Mercury, Venus, Mars, Saturn and Jupiter -- the Great Planetary Alignment of 2002. No longer. Saturn and Mercury are now too close to the Sun to see without hurting your eyes, and Mars is fading fast. Jupiter and Venus are all that's left.

Even so, the western sky remains attractive. Go outside after dinner and see for yourself: it only takes two planets to make a lovely show.

Editor's Note: If you're watching Venus set in late May or early June (around 10:30 p.m. local time at mid-northern latitudes) and the planet looks odd, grab your binoculars for a closer look. You may have spotted an elusive Venus pillar. Their cousins, Sun pillars, are well-known: When the Sun is rising or setting, ice crystals in cirrus clouds can reflect sunlight and cause vertical columns of light to spring upward from the horizon. It's a mirage, and it only happens to very bright objects such as the Sun and Moon ... and sometimes Venus.

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These sky maps show the appearance of the western sky after sunset from mid-northern latitudes:

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Right: The solar system on June 3, 2002. Venus and Jupiter will appear close together in the sky, but they are really very far apart. Courtesy NASA Liftoff.

Venus Pillars and Dogs -- (Science@NASA) If you look at Venus this month and something doesn't seem quite right, you may have spotted a rare Venus pillar ... or better yet, a Venusdog!

Relax, It's Only April -- (Science@NASA) The five brightest planets converged in the western sky for an eye-popping show in May 2002. [gallery]

Learn more about the Star of Bethlehem: A Christmas Star for SOHO (Science@NASA); The Star of Bethlehem: An Astronomical and Historical Perspective (Susan S. Carroll); Star of Bethlehem (Griffith Observatory)

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