a day ago
How to see the letters X and V on the moon tonight
The full moon is a glorious sight, and the sliver of a brand-new moon a wispy delight, but tonight's first-quarter moon has its own unique treat — for a few hours, you can make out the letters X and V on the lunar surface. Here's how.
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As the photo shows, the lunar X appears about a third of the way from the bottom of the moon, while the Lunar V is a little above the centre. Both features straddle the line between the light and dark sides of the moon, known as the terminator, with the X appearing a little into the dark side, and the V closer to the light side.
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Why do the letters appear?
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They're not really there on the surface, and you can't see them at any other time. What you're looking at is called the 'clair-obscur' effect, in which the play of light and shadow on the surface creates the appearance of shapes; in this case, giant letters, formed by the partially lit edges of craters.
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According to British astronomer Mary McIntyre, the effect kicks off tonight at about 7:30 p.m. ET, and should last about four hours. That means by the time the sun has set and the moon is at its brightest, you should be able to get a good look, clouds permitting.
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What's the best way to see them?
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Naked eye is a little tricky, since they are quite small. But decent binoculars (or better yet a small telescope) should bring them into focus.
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Humans have been looking at the moon since we were human, and through telescopes since they were invented, so it's not surprising that other transient shapes have been noticed and given evocative names, including the jewelled handle, Cassini's moon maiden, Plato's hook and the eyes of Clavius, not to mention the so-called 'man in the moon' that many people see in the full moon.
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McIntyre has a chart of when to look for them, while BBC's Sky at Night Magazine has a nice picture that shows their locations. The best part about all this is that if you miss them, they'll come back again every 28 days, forever.
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