Fall Equinox Full Moon

Written by The Night Sky Guy on September 22, 2010 – 4:26 pm -

Officially changing seasons at 11:09 pm ET tonight, Autumn will be  welcomed in by a giant full Moon for the first time in 20 years!  The word equinox comes from Latin meaning “equal night” and refers to the 12 hour long day and night that occurs only on this particular day of the year.

Skywatchers looking at the mid-day position of the sun over the summer season will notice that it has been slowly sinking closer to the southern horizon, resulting in ever longer shadows. On the autumnal equinox the Sun reaches its halfway point in its migration towards its lowest point in the midday sky, which happens on the December solstice. It’s only on the spring and autumnal equinox that the Sun rises due east and sets due west.

Astronomically speaking the September equinox marks one of the four major turning points in the cycle of seasons. The Earth spins on its axis, which is tilted at 23.5 degrees with respect to its orbital plane. On these days however the Earth’s axis is neither tilted away nor towards the Sun, but has both northern and southern hemispheres experiencing equal amounts of sunshine.

The equinox is really a geometrical alignment of the Earth with the Sun, when the sun appears positioned right above our planet’s equator. As autumn progresses the Sun appears to continue its travels south until the winter solstice, when it slowly begins its journey north.

As the golden orb rises in the eastern sky as the sun sets int he west you may notice a superbright star next to it – that is the planet Jupiter.  Together the pair will ride high into the southern sky  int he overnight hours and set in the west as the sun rises in the east.

Adding to the celestial delight will be Jupiter parking itself as close as it will get this year to the seventh and most elusive planet in the solar system – Uranus.  The planetary duo will be separated by less than 1 degree – meaning they will only be 2 full moon disks apart! Promises to be quite a sight in binoculars and particularly through small telescopes. don’t worry if you miss the show tonight – the two planets will remain close for the upcoming few months -  but what’s a few million miles between  friends, eh?

Uranus and Jupiter at its moons s seen int he sky this week. Courtesy of Jin Lu of Tempe, Arizona.

Uranus and Jupiter at its moons as seen in the sky this week. click image to enlarge. Photo courtesy of Jin Lu of Tempe, Arizona.


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