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Venus and Mercury
Mercury is a frustrating little planet. It’s one of our closest neighbors, passing within about 50 million miles of Earth. Yet because it’s the closest planet to the Sun, it seldom moves far enough from the Sun in our sky for good viewing.
But tonight offers an especially good view of Mercury because it climbs well up into the evening twilight. It’s in the western sky at sunset and looks like a bright star.
And an even brighter beacon helps point the way: the second-closest planet to the Sun, Venus — the brilliant “evening star.” Mercury is roughly half a degree to the right or lower right of Venus — roughly the width of a pencil held at arm’s length. The planets will remain close for several nights, offering a little extra time to catch Mercury.
Because Mercury stays so close to the Sun, it’s a tough world to study. Most research telescopes can’t aim close to the Sun because the sunlight would overpower their instruments. And even when Mercury is far enough from the Sun to observe with a telescope, it stays so low in the sky that the view is blurred and distorted by the atmosphere.
By far the best view of Mercury has come from spacecraft. In particular, MESSENGER has been orbiting Mercury since 2011. It has mapped Mercury’s surface in detail, and probed the planet’s interior. But its mission to Mercury is scheduled to end this spring — once again leaving us without a good view of this close but hard-to-study little planet.