What's In The Sky

Stargazing for December


The big event for December will occur on Dec. 20. On that night, we'll experience our first total lunar eclipse in three years. The eclipse will start at about 9:30 p.m., and will be total from about 11:45 p.m. until about 1 a.m.

So just what is a lunar eclipse? And how will it look? A lunar eclipse occurs when the Earth moves between the Sun and the Moon. Lunar eclipses occur when the Moon is full, and thus brightly lit.

As the Earth moves in front of the Moon, the bright lunar surface begins to darken, eventually turning a bright to deep red, a very impressive sight.

In the early stages of the eclipse, called the penumbral stage, the Moon is only partly illuminated. If you were on the Moon, you'd see part of the Sun blocked by the Earth, but not the entire Sun.

The curved shadow of the Earth is easily seen on the Moon at this time. The Greek scientist Aristotle deduced from the curved shadow that the Earth was indeed a sphere.

Unlike the Sun during a full solar eclipse, during a lunar eclipse the Moon is still visible. The reddish color is caused by sunlight being bent as it passes through Earth's atmosphere, before reaching the Moon. Longer wavelength light, mainly red, is not scattered as much by the atmosphere and more of it makes it through to the Moon. Thus, the Moon is reddish in color, much like the ruddy hues we see here on Earth at sunset and sunrise.

The eclipse will darken the skies noticeably, as the bright Moon is eclipsed. Look for the star cluster Pleiades to the right of the Moon. With binoculars, look to the left of the Moon, about 6 moon-widths away, and see if you can pick out a dazzling cluster of stars, called M35.

When lunar eclipses occur, they are visible over a wide area of the Earth, unlike solar eclipses which are visible in very small areas. Most of the US will be able to see the December eclipse. The eastern US will see the eclipse later at night; Hawaii will see it in the evening sky. The odds that we'll have clear skies on Dec. 20 are not very good, but we can always hope!

Jupiter remains in good position for evening viewing in December, along with its four bright Galilean moons. On Dec. 3, 13, 17, and 27, the four moons will be all on one side of the planet, in a straight line. Check them out with binoculars if skies are clear. This will be the last good month to view Jupiter, as it pulls away from us in its march around the Sun.

We know when full Moon will be this month -- Dec. 20. New Moon will occur on Dec. 6. On Dec. 13, the first-quarter Moon will join Jupiter, low in the western evening sky. On Christmas Eve, when the kids are anticipating Santa's arrival, watch the waning gibbous Moon rise at about 9:30 p.m., located near the bright star Regulus in the constellation Leo.

The constellations continue their march across the night sky in December. This month marks the first really good month to view winter's gem, Orion. The great hunter will be well above the horizon by 9 p.m., even at the start of the month. Look for bright, reddish Betelgeuse forming the left shoulder (as we view it), and white Rigel as the lower right leg. With binoculars, look at Orion's sword, and see if you can pick out a fuzzy patch, the Orion nebula.

Enjoy the December skies, and happy holidays to all!


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