When the Sun sets in the evening of Saturday, March 20, 2010, it will be crossing the celestial equator, as spring begins in the Northern Hemisphere and autumn in the Southern. See the equinox as the Moon and Pleiades are close together.





On Saturday night, March 20, 2010, the Sun will be crossing the celestial equator, going from the southern portion of Earth's orbital plane to the northern part.

It is one of two days each year in which the length of the day is approximately identical to the length of the night.



As such, it is called the equinox'”spring (vernal) equinox for the Northern Hemisphere and fall (autumn) equinox for the Southern Hemisphere.

All of this happens because the Earth is tilted about 23.5 degrees on its axis of rotation with respect to the plane of its orbit around the Sun.

So, on about half of its orbit around the Sun the Earth is tilted away from the Sun, and on the other half it is tilted toward the Sun.

Specifically, during two points on its orbit, the Sun is crossing the celestial equator, which means that nearly equal amounts of sunlight are falling on the Northern Hemisphere and the Southern Hemisphere, and the amount of daylight and amount of darkness at night are approximately of equal length.



Along with this equinox event, the Moon will also be about one-third of the way above the horizon on the evening of March 20, 2010--just after the Sun sets.

Look toward the western portion of the sky, just about the time that the Sun fades completely from view and darkness sets in.



And the Moon will be closely joined by the Pleiades, an open star cluster within the constellation Taurus. View the Moon and Pleiades with at least binoculars, for the best possible viewing experience.



On page two, check out a Sky Map of the March 20, 2010 evening sky at SpaceWeather.com's webpage 'Happy Equinox.'









Also called the Seven Sisters (or Messier object 45), the Pleiades are among the closest star clusters to our Solar System, and also one of the more noticeable ones in the night sky due to its very luminous grouping of stars.The Seven Sisters refer to the seven stars that are visible to the naked eye, here on Earth. They are Sterope, Merope, Electra, Maia, Taygete, Celaeno, and Alcyone.

Together they look like a little dipper, but not the real Little Dipper, or the constellation Ursa Minor (Little Bear) in the Northern Hemisphere.



See a picture of their position in relation to each other at 'The Pleiades.'



According to the March 19, 2010 NASA article Equinox Sky Show, '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.'

Page three concludes with more interesting stuff to see on Saturday night as you look up into the night sky.





Learn more about Mid-Atlantic Occultations to early April 2010 at ' This is the last Pleiades occultation for the USA until 2023! 'It begins, 'For non-astronomers, "occultation" is a term that astronomers use for an eclipse of a star by an asteroid or by the Moon.'

And, learn more about "Earthshine," something you'll see Saturday night, as you look at the crescent Moon.

Check out the 10.4.2005 NASA article The Da Vinci Glow, which states, "Five hundred years ago, Leonardo Da Vinci solved an ancient astronomical riddle: the mystery of Earthshine."



