The Evening Sky in December 2016
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The Evening Sky in December 2016
Venus is the brilliant ‘evening star’ appearing due west at sunset and setting toward the southwest after midnight. Above and right of Venus, and much fainter, is orange Mars. Below and left of Venus is Mercury, setting about 90 minutes after the Sun till mid-month. After the 15th Mercury sinks into the twilight as it passes between the Earth and the Sun. None of these planets is of much interest in a telescope. Venus looks like a tiny gibbous Moon. Mars and Mercury appear very small. The very thin crescent moon will be below and right of Mercury on the 1st, below Venus on the 3rd, and below Mars on the 5th.
The brightest true stars are in the east and south. Sirius, the brightest of all the stars, is due east at dusk, often twinkling like a diamond. Left of it is the bright constellation of Orion. The line of three stars makes Orion's belt in the classical constellation. To southern hemisphere skywatchers they make the bottom of 'The Pot'. The faint line of stars above and right of the three is the Pot's handle. At its centre is the Orion Nebula, a glowing gas cloud nicely seen in binoculars. Rigel, directly above the line of three stars, is a hot blue-giant star 770 light years* away. Orange Betelgeuse, below the line of three, is a cooler red-giant star 430 light years away.
Left of Orion is a triangular group making the upside down face of Taurus the bull. Orange Aldebaran is the brightest star in the V shape. Aldebaran is Arabic for 'the eye of the bull'. Still further left is the Pleiades /Matariki/Subaru cluster, a tight grouping of six naked-eye stars impressive in binoculars. It is 440 light years away.
Canopus, the second brightest star, is high in the southeast. Low in the south are the Pointers, Beta and Alpha Centauri, and Crux the Southern Cross upside down at this time of the year. In some Maori star lore the bright southern Milky Way makes the canoe of Maui with Crux being the canoe's anchor hanging off the side. In this picture the Scorpion's tail, just setting, can be the canoe's prow and the Clouds of Magellan are the sails.
The Milky Way is wrapped around the horizon. The broadest part is in Sagittarius low in the west at dusk. It narrows toward Crux in the south and becomes faint in the east below Orion. The Milky Way is our edgewise view of the galaxy, the pancake of billions of stars of which the sun is just one. The thick hub of the galaxy, 30 000 light years away, is in Sagittarius. The nearby outer edge is the faint part of the Milky Way below Orion. A scan along the Milky Way with binoculars will show many clusters of stars and a few glowing gas clouds.
The Clouds of Magellan, LMC and SMC, high in the southern sky, are two small galaxies about 160 000 and 200 000 light years away, respectively. They are easily seen by eye on a dark moonless night. The larger cloud is about 1/20th the mass of the Milky Way galaxy, the smaller cloud 1/30th but that is still many billions of stars in each.
Very low in the north is the Andromeda Galaxy seen in binoculars in a dark sky as a spindle of light. It is a bit bigger than our Milky Way galaxy and nearly three million light years away.
Jupiter (not shown) is the brightest 'star' in the morning hours, shining with a steady golden glow. It rises due east before 4 a.m. at the beginning of the month and before 2 a.m. by the New Year. A small telescope will show Jupiter’s disk and its four large moons lined up on either side of the planet. Good binoculars, held steadily, will sometimes show one or two of the moons.
*A light year (l.y.)is the distance that light travels in one year: nearly 10 million million km. Sunlight takes eight minutes to get here; moonlight about one second. Sunlight reaches Neptune, the outermost major planet, in four hours. It takes sunlight four years to reach the nearest star, Alpha Centauri.