Equinox Sky Show

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.

A similar Moon-Pleiades conjunction photographed by Marek Nikodem of Szubin, Poland, in July 2009.

The Pleiades are a cluster of young stars some 440 light years from Earth. They formed from a collapsing cloud of interstellar gas about 100 million years ago. By the standards of astronomy, that's really young. The Earth under your feet is almost 50 times older. Dinosaurs were roaming our planet long before the Pleiades popped into being.

Only about seven of the Pleiades are visible to the unaided eye. The "Seven Sisters" are Sterope, Merope, Electra, Maia, Taygete, Celaeno and Alcyone, named after daughters of the mythological Greek god Atlas. Together, they form the shape of a little dipper, which is why the Pleiades are often mistaken for the Little Dipper, an asterism of Ursa Minor.

Binoculars are highly recommended for this event.

First, scan the Moon. You'll see craters, mountains and lava seas. Note that you can see the entire Moon, not just the brightly-lit crescent. The Moon's dark terrain is illumined by a ghostly glow called "Earthshine." It is the light of our own blue planet shining down on the Moon.
Next, scan the sky around the Moon. The Pleiades come into sharp focus---and they are more than seven. Dozens of faint "sisters" can be seen through even modest optics.

This night doesn't sound equal. It sounds much better than that.

Experience the equinox!

The Wizard Nebula

This image of the open star cluster NGC 7380, also known as the Wizard Nebula, is a mosaic of the images from the WISE mission spanning an area of the sky of about 5 times the size of the full moon. NGC 7380 is located in the constellation Cepheus about 7,000 light years from Earth within the Milky Way Galaxy. The star cluster is embedded in a nebula, which span some 110 light years. The star of NGC 7380 have emerged from this star-forming region in the last 5 million years or so, making it a relatively young cluster.

WISE, the Wide-field Infrared Survey Explorer mission, scans the entire sky in infrared light, picking up the glows of hundreds of millions of objects and producing millions of images. The mission is designed to uncover objects never seen before, including the coolest stars, the universe's most luminous galaxies and some of the darkest near-Earth asteroids and comets. It vast catalogs will help answer fundamental questions about the origins of planets, stars and galaxies.

WISE join two other infrared mission in space - NASA's Spitzer Space Telescope and the Herschel Space Observatory, a European Space Agency mission. WISE is different these missions in that it will survey the entire sky. It is designed to cast a wide net to catch all sorts of unseen cosmic treasures, including rare oddities. All four infrared detectors aboard WISE were used to make this image.

NGC 7380 was discovered by Caroline Herschel in 1787. Her brother, William Herschel, discovered infrared light in 1800.