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The Sky This Week, 2013 November 26 - December 3

The "Thanksgiving Star", and a guest for the holidays?

The 36-inch James Lick telescope at Lick Observatory,
Mount Hamilton, CA, dedicated in 1888

This telescope was used by E.E. Barnard to discover Amalthea,
the innermost moon of Jupiter, on September 7, 1892.

The Moon wanes in the pre-dawn sky this week, diving southward along the Ecliptic as she wends her way through the rising springtime constellations. New Moon occurs on December 2nd at 7:22 pm Eastern Standard Time. Look for the Moon just over five degrees south of ruddy Mars on the morning of the 27th. Luna’s slimming crescent lies just under three degrees west of the bright blue star Spica at dawn on the 29th.

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; 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 the Great Winter Circle reaches prominence as the midnight hour approaches. This yellow-hued star, known as Capella, is nearing the meridian at this time, and its transit is entirely appropriate for the upcoming Thanksgiving holiday. Capella is one of the few bright stars whose name does not have Arabic origins. It derives from the Latin word for a female goat, and if you have keen eyes or a pair of binoculars you can see a small triangle of stars tucked close to the bright yellow beacon. These stars form an asterism known as "The Kids". In Roman mythology Capella represented the she-goat Amalthea, which suckled the infant Jupiter. The young god, evidently a rambunctious little boy, accidentally snapped off one of Amalthea’s horns, which became the "Cornucopia", or "Horn of Plenty". In turn the Cornucopia has become associated with our observance of Thanksgiving and the feasting that goes along with it. Amalthea has also been recognized by giving her name to the fifth moon of Jupiter, discovered by the keen-eyed American astronomer Edward Emerson Barnard in 1892 on his first night of observing with the then-new 36-inch refracting telescope at Lick Observatory, the largest in the world at the time. 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!

Venus continues to brighten the early evening sky, attracting quite a bit of attention to the southwest as twilight deepens. Thos week she sets at her latest time for the year, around 7:40 pm EST here in Washington. As December opens she begins to overtake the Earth on her faster inner solar orbit. For us this means that she begins to inch toward the Sun and set earlier each night. This effect will be fairly gradual over the next couple of week, but by the last week of the year she will seem to sink like a stone into the solar glare.

Jupiter rises about four minutes earlier on each successive night, and by the week’s end he’s cresting the horizon just before 7:30 pm. You can get a good bead on him in the small telescope by 10:00 pm and enjoy watching the planet’s fast rotation and dancing moons for the rest of the night. If you’ve got a telescope on somebody’s "wish list" for Christmas Old Jove makes a great target to try it out on before you gift it. Who knows, maybe you’ll want one on your wish-list as well!

Mars rises at around 1:00 am, so he’s best seen in the hours before dawn. The red planet is drifting eastward below the stars of the hindquarters of Leo, the Lion. The red planet is gradually brightening and is now comparable to the bright star Regulus, the lead star of Leo. The two objects offer a very nice color contrast between Mars’ distinct pinkish hue and the blue-white tint of the star. Mars is still a tough object for the telescope, but over the course of the rest of the year his disc will grow and start to reveal features to the patient observer.

Comet ISON reaches perihelion, its closest point to the Sun, on Thanksgiving Day. It will nearly skim the surface of Old Sol, passing a mere 1.12 million kilometers (700,000 miles) above the white-hot solar photosphere. The environment here can only be described as "hellish", with temperatures measured in thousands of degrees and intense tidal forces all trying to rip the fragile comet nucleus apart. If the comet survives this encounter it will gradually become visible in the evening sky by the second week of December. At this time it may be an easy naked-eye object or it may be…gone! We should know more by this time next week.

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