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The longest nights: in the eastern sky, a tall tower of dazzling stars heralds the advent of winter.

   'Tis the year's midnight, and it is the day's:
   Lucy's, who scarce seven hours herself unmasks.
   The sun is spent, and now his flasks
   Send forth light squibs, no constant rays;
   The whole world's sap is sunk ...

   --John Donne, A Nocturnal upon St. Lucy's Day,
   Being the Shortest Day

St. Lucy's day is December 13th, but it was once considered to be the shortest day of the year. The name Lucy means "light," and in parts of Scandinavia girls still don a headpiece decked with candles to bring light to the world at its time of deepest darkness.

Many cultures around the world hold festivals of light to symbolize cheer and hope in this season of the shortest days. Astronomers have their own headpiece of lights to put on at this time of year. It's the tower of bright constellations dominating the east on these December evenings.

Tower of brilliance. What are the components of this tower? Look at the all-sky map in the center of this issue and turn it around so its "Facing East" horizon is at the bottom, right-side up. Just above that horizon is bright Orion. Betelgeuse and Rigel, his shoulder and knee (or foot) stars, outshine even his irresistible three-star Belt, now nearly vertical. Left of Orion, low in the east-northeast, is Gemini, dominated by Pollux and Castor.


But Orion and Gemini are just the base of the tower, which reaches all the way to the zenith.

The zenith is held by the bright constellation Andromeda, the chained maiden of Greek mythology. Andromeda contains three 2nd-magnitude stars in a long, gentle arc. The western end of the arc is Alpheratz, the star that Andromeda loans to help form the Great Square of Pegasus. Alpheratz is already a little past the zenith.

Cassiopeia, the constellation of Andromeda's mother, stands to her left as you face east and crane your head up to look overhead.

Turning elsewhere for a moment, the mythological Andromeda was chained to await a sea monster represented by Cetus, the Whale. Cetus is in the trailing (eastern) edge of a vast region of sky dimness: the Water or Great Celestial Sea, lower in the southeast to southwest.

Just as Andromeda needed to be rescued from the sea monster, we're now being rescued from too long an expanse of this dim sky. In the myth, her rescuer was the hero Perseus. In the sky, Perseus floats just below Andromeda and her bright zigzag of a mother.

Perseus is brighter overall than Andromeda but has only two 2nd-magnitude stars, and one of them isn't always 2nd magnitude. I'm talking about Beta Persei, the bright eclipsing binary Algol, which dips from magnitude 2.1 to 3.4 for a few hours every 2.867 days.

To the right of Perseus (again facing east and craning our necks) is little Aries. It's not much as constellations go but adds a couple of stars to the overall tower of light.

There's one more story of brightness in our tall tower, below Perseus and Aries but above Orion and Gemini. This consists of Auriga the Charioteer on the left, with blazing Capella, and Taurus the Bull on the right, featuring Aldebaran, the Pleiades, and the Hyades.

Night festival. Astronomers actually like long nights--as long as those nights are clear and full of their special bright lights. So we can celebrate with Lucy:
   Let me prepare towards her, and let me call
   This hour her vigil, and her eve; since this
   Both the year's and the day's deep midnight is.

Fred Schaaf welcomes your comments
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Title Annotation:Northern Hemisphere's Sky
Author:Schaaf, Fred
Publication:Sky & Telescope
Geographic Code:1USA
Date:Dec 1, 2011
Previous Article:5 binocular factors that matter: to see, or not to see--that is the question.
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