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The Sky This Week, 2011 November 22 - 29

A most unusual eclipse and a sign of the season.

 Jupiter, with Io, Europa & its shadow
Imaged 2011 NOV 19

The Moon returns to the evening sky by the week’s end. New Moon occurs on the 25th at 1:10 am Eastern Standard Time. At this time the Moon will cause a rather unusual partial solar eclipse that will only be visible from Antarctica. While the entire continent will see the eclipse in varying degrees of partiality, maximum eclipse occurs at local midnight just west of the Antarctic Peninsula near the small speck of land known as Peter Island. There about 90% of the Sun’s face will be covered by the Moon as the Sun dips to touch the horizon. If you were aboard a satellite orbiting just 500 kilometers (300 miles) above this point you’d see a total eclipse! For the rest of us in more temperate climes we must settle for spying the young lunar crescent as she climbs past bright Venus in the southwestern sky on the evenings of the 26th and 27th.

Thanksgiving marks the beginning of the winter holiday season for many of us. We’re now entering the weeks when we experience the year’s earliest sunsets and nightfall seems to come well before we’re ready to end our day. It is a time of great seasonal shifts in both the climate and the sky. It is a time when I finally "let go" of the last of summer’s constellations even though the Summer Triangle is still prominent in the early evening. By the time the dinner hour is finished and the telescope has been set up and allowed to cool down these stars are nearing the western horizon and the rising stars of the Winter Circle are beginning to demand my attention. The flashes of color in these bright stars remind me that they will be my nighttime companions for the next several months as winter presses into spring. The northernmost star in this large asterism now reaches great prominence as the midnight hour approaches. The yellow-hues star Capella passes almost directly overhead at this time, and its passage is entirely appropriate for the upcoming Thanksgiving holiday. In Roman mythology the star represented a she-goat named Amalthea which suckled the infant Jupiter. The young god accidentally snapped off one of the goat’s horns, which became the "Cornucopia", or "Horn of Plenty". Amalthea has been recognized by giving her name to the fifth moon of Jupiter, discovered by the American astronomer Edward Emerson Barnard in 1892. This was the last moon in the solar system to be found visually. Thanks to Earth-based and spacecraft photography we now know that Jupiter has some 64 moons!

The bright planet Venus is now beginning to climb rapidly away from the horizon into the evening sky. By the week’s end she sets an hour and a half after the Sun, dipping below the horizon just at the end of evening astronomical twilight. Over the course of the rest of the year she will continue to climb to prominence in darker skies, and she will remain a fixture in the evening sky for the first half of next year. Look for the day-old crescent Moon below and to the right of Venus on the evening of the 26th. If you don’t see Luna then, she will be above the dazzling planet on the following night.

While Venus begins to gain a foothold in the night sky, Jupiter is the planet that now dominates it. Old Jove becomes visible just after sunset in the east, and by the end of evening twilight he attracts almost all the attention. Jupiter is very bright because the planet is very large. Even though sunlight at Jupiter’s distance from the Sun is only about 25% of the level it is here on Earth the giant planet’s huge girth reflects quite a bit of it back toward us. Jupiter’s diameter is over 10 times that of our home planet which means its surface area is some 100 times that of Earth and its volume could contain over 1000 bodies of earth’s size! Jupiter offers the most generous-sized disc for telescopic viewing of any of the planets, and while we can marvel at fine details in large telescopes on still nights we must remember that those details are the size of continents here on good old Terra! Even casual observations will show dramatic changes in Jupiter’s clouds over a few nights, which means that the weather on Old Jove must be not only spectacular but incredibly violent. Superlatives don’t really do this distant world proper justice, but they help us understand what we see when we gaze at Jupiter across some 400 million miles of space.

From the vastness of Jupiter we next turn to the diminutive planet Mars. Roughly half the Earth’s size, the red planet has tantalized us for years. Currently located in the constellation of Leo, the Lion, Mars is a small pink dot in the eyepiece when compared to Jupiter, but generations of astronomers have studied its rusty surface from afar and will continue to do so for generations to come. If all goes well this week our most ambitious robot emissary to Mars will leave its Florida launch pad on the way to an August landing. The Mars Curiosity Rover is the size of a small car and will hopefully roam an ancient martian lakebed for at least two years after its arrival.

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