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March 19, 2010: When the sun sets on Saturday, March 20th, a special kind of night will fall across the Earth. It's an equal night. Or as an astronomer would say, "it's an equinox." It's the date when the sun crosses the celestial equator heading north. Spring begins in one hemisphere, autumn in the other. The day and night are of approximately equal length. To celebrate the occasion, Nature is providing a sky show. It begins as soon as the sky grows dark. The Moon materializes first, a fat crescent hanging about a third of the way up the western sky. Wait until the twilight blue fades completely black and you will see that the Moon is not alone. The Pleiades are there as well. The Moon and the Pleiades are having a close encounter of rare beauty. There's so little space between the two, the edge of the Moon will actually cover some of cluster's lesser stars. According to David Dunham of the International Occultation Timing Association, this is the best Moon-Pleiades meeting over the United States until the year 2023. Right: A similar Moon-Pleiades conjunction photographed by Marek Nikodem of Szubin, Poland, in July 2009.

This week, Mercury is emerging from the glare of the sun and making a beeline for Venus. By week's end, the two planets will be just 3o apart, an eye-catching pair in the deep-blue twilight of sunset. The best nights to look are April 3rd and 4th. Go outside at the end of the day and face west. Venus pops out of the twilight first, so bright it actually shines through thin clouds. Mercury follows, just below and to the right: April 3April 4 Venus is an old friend to most sky watchers; Mercury, less so. The first planet from the sun spends most of its time wrapped in painful sunlight. Seeing it so easily, and in the beautiful company of Venus no less, is a rare treat indeed. The next apparition this good won't come until Nov. 2011. By that time, however, we'll have much better view of Mercury all the time. NASA's MESSENGER probe is en route to Mercury now, and in March of 2011 it will become the first spacecraft to orbit the planet. During a year-long science mission, MESSENGER will beam back a stream of high-resolution pictures and data obtained using seven instruments designed to operate in the extreme environment near the Sun. This kind of coverage of planet #1 is unprecedented.

Imagine you're a Brontosaurus1 with your face in a prehistoric tree top, munching on fresh leaves. Your relatives have ruled planet Earth for more than 150 million years. Huge and strong, you feel invincible. You're not. Fast forward about 65 million years. A creature much smaller and weaker dominates the Earth now, with brains instead of brawn. Its brain is a lot larger relative to its body size – plenty big enough to conceive a way to scan the cosmos for objects like the colossal asteroid that wrought the end of your kind. Right: An artist's concept of NASA's Wide-field Infrared Survey Explorer (WISE). [more] The creature designed and built WISE, NASA's Wide-field Infrared Survey Explorer, to search for "dark" objects in space like brown dwarf stars, vast dust clouds, and Earth-approaching asteroids. WISE finds them by sensing their heat in the form of infrared light most other telescopes can't pick up.