for National Geographic News
Skywatchers across the world are in for a celestial treat Monday night as two of the brightest naked-eye planets, Venus and Jupiter, join a thin crescent moon to create a brief "unhappy face" in the sky.
The planets appeared closest together—an event known as a planetary conjunction—Sunday night.
"This is set to be the best planetary gathering of the year, simply because it involves three of the brightest objects in the sky after the sun," said Geza Gyuk, director of astronomy at the Adler Planetarium in Chicago.
"As long as you have clear skies in the early part of the evening, this is one astronomical event that's hard to miss."
In fact, some historians think that a similar conjunction between Jupiter and Venus in 2 B.C. may be the source of the "star of Bethlehem" story related in the Bible.
The stellar pair would have appeared so close together, scholars think, that they might have seemed to meld into one brilliant beacon of light.
Blocked by a Thumb
Of the eight official planets in the solar system, five are visible at night without the aid of a telescope or binoculars.
Jupiter and Venus are particularly bright, partly because both have highly reflective clouds that completely envelop them, but also because Venus is Earth's closest neighbor while Jupiter is the largest planet in the solar system.
Both planets are currently easy to locate just after sunset in the southwestern sky.
During a conjunction, two or more of the naked-eye planets seem to be huddled close together—but this proximity is misleading.
For example, on the flat plane of the sky, Jupiter and Venus look like they have been drawing closer together over the past month. But in three dimensions the planets are actually separated by nearly 500 million miles (805 million kilometers).
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