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Sky Watch by J. Alex Knoll

Our closest approach to the sun does make for the shortest season

Twilight Thursday and Friday evening reveals the new crescent moon low in the southwest with Venus blazing a few degrees away tight against the horizon. Venus sinks lower in the early evening sky over the next week, finally disappearing between the sun and earth on January 11. Then, after a few days absence, it reappears in pre-dawn skies, where it will blaze as the Morning Star until autumn.

This time of year a day is 30 seconds longer

Winter officially begins with the solstice Saturday, December 21. At 12:11pm EDT that day, the sun reaches its most southerly declination, standing still above the Tropic of Capricorn. For the roughly 90 percent of the world’s population that lives in the Northern Hemisphere, this is the first day of winter, the day of the longest night and the shortest day of the year.

Can the Geminids outshine December’s full moon?

The moon lights up the night this week, starting as a waxing gibbous, reaching full moon Tuesday and waxing slowly through the middle of the week. Look for the near-full moon beside the Pleiades star cluster Saturday.

While never the comet of the century, it piqued our curiosity

It’s official: comet ISON is no more. NASA confirmed Tuesday that after its first-ever venture from the outer limits of the solar system to the sun, the comet did not survive the onslaught of solar radiation. Born 4.5 billion years ago during the formation of the solar system, ISON had resided in the so-called Oort Cloud a full light-year away. Roughly a million years ago, perhaps after a cometary collision, ISON began its journey toward the sun.

See if you can find the naked-eye five

The waning crescent moon rises later and later in pre-dawn skies through the weekend before disappearing behind the sun with Tuesday’s new moon.

Comet ISON is heading for the sun

If you haven’t looked for Comet ISON yet, now is the time. In just the past few days, the comet has grown more than 15 times brighter and is now visible to the unaided eye low in the east-southeast before dawn.

The interloper visits Spica and Mercury

Mercury is putting on its best pre-dawn show of 2013, more than doubling in brightness this week, from +1 magnitude to –0.5 (each order of magnitude is exponential, so an increase from +1 to 0 is a doubling). Monday marks the innermost planet’s greatest elongation — its farthest point away from the sun as seen from earth and its highest point above the horizon. Mercury rises a little before 6am and climbs nearly 15 degrees above the southeast horizon before the sun rises more than an hour later.

Planets and clusters and meteors

As the sun sets around 5pm, Venus blazes in the south-southwest. Our sister planet is at its farthest point east of the sun. But the geometry between Venus, the sun and earth doesn’t add up to a better view, as the evening star climbs only a dozen degrees above the horizon and sets within 90 minutes of the sun. Still, Venus is near impossible to miss, and Thursday evening it is joined by the waxing crescent moon a little higher in the sky.

Even a partial eclipse can be blinding

The last day of October marks the mid-point between autumnal equinox and winter solstice, one of four cross-quarter days in the passage of the earth around the sun. The day has been recognized for millennia, celebrated as Samhein, The Day of the Dead and All Hallow’s Eve, or Halloween.

The brightest Evening Star

Sunset finds Venus ablaze low in the southwest before setting by 8pm. There is no brighter planet or star, and so close to the horizon Venus can pulse and shimmer as its light is distorted by our atmosphere. Traveling close to the sun, Venus appears for at most a few hours either after sunset or before dawn. This led early civilizations to believe that the evening star and the morning star were two distinct objects. The ancient Greeks called the morning Venus Phosphoros and the evening apparition Hesperos.