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The Sky This Week from December 21 to December 30

Winter nights begin with great views of the brightest star and two fine star clusters, and wrap up with the brilliant planets Venus and Jupiter.

Wintersolstice
Winter Solstice 2014
Winter solstice, which occurs when the Earth's North Pole is maximally tilted away from the Sun, marks the start of winter in the Northern Hemisphere. The photographer captured this beautiful image during the winter solstice on December 21, 2014, just after sunset.
Jon Bunting/Flickr
Friday, December 21
Earth’s winter solstice occurs at 5:23 p.m. EST. At that moment, the Sun reaches its farthest point south in the sky. The solstice marks the official beginning of winter in the Northern Hemisphere, and tonight has more hours of darkness than any other. From mid-northern latitudes, however, the earliest sunset occurred about two weeks ago and the latest sunrise won’t happen until early January.

Saturday, December 22
Full Moon officially arrives at 12:49 p.m. EST, but our satellite looks completely illuminated all night. You can find it rising in the east just after sunset and peaking in the south shortly after midnight local time. It dips low in the west by the time morning twilight begins. As the Full Moon closest to the winter solstice, it climbs higher in the sky than any other Full Moon during the year. It lies among the background stars of western Gemini tonight, near the feet of the Twins.

Sunday, December 23
Mercury remains a nice sight in predawn twilight for the next several days. This morning, the innermost planet lies 7° above the southeastern horizon 45 minutes before sunrise. Mercury shines at magnitude –0.4, easily bright enough to see with the naked eye (although binoculars will help you pick it out of the twilight glow). Simply look 2° to the lower left of brilliant Jupiter, which shines about four times brighter than the inner world. When viewed through a telescope, Mercury appears 6" across and shows a gibbous phase.

Monday, December 24

The solar system’s two outer planets both have close encounters with stars this evening. Look for Uranus some 60° above the southern horizon around 7:30 p.m. local time. The magnitude 5.7 world lies in southeastern Pisces, 1.3° north of 4th-magnitude Omicron (ο) Piscium. Although Uranus shines brightly enough to glimpse with the naked eye under a dark sky, use binoculars to locate it initially. A telescope reveals the planet’s 3.6"-diameter disk and striking blue-green color as well as a neighboring point of light that looks a bit like a moon. But this is actually a 9th-magnitude field star that slides 1' south of Uranus this evening. Once you’ve finished viewing Uranus, turn your scope toward Neptune. The magnitude 7.9 world lies 2.2° east of 4th-magnitude Lambda (λ) Aquarii, an area that appears 30° high in the southwest at 7 p.m. local time. This evening, Neptune lies 15' (half the Full Moon’s diameter) due south of 6th-magnitude 81 Aqr. Higher magnifications reveal Neptune’s blue-gray disk, which spans 2.3".

The Moon reaches perigee, the closest point in its orbit around Earth, at 4:49 a.m. EST. It then lies 224,353 miles (361,062 kilometers) away from us.
Orion_030512
Sirius and Orion

The main constellations of the Northern Hemisphere’s winter sky are on display in this scene that includes La Ventana Arch in El Malpais National Monument in New Mexico in the foreground. Orion the Hunter stands in the upper right corner and the sky’s brightest star, Sirius, lies in line with Orion's Belt and just to the right of center.

John A. Davis
Tuesday, December 25
If you’re looking for a Christmas star to mark the holiday, you can’t go wrong with brilliant Sirius. The brightest star in the sky (after the Sun, of course) gleams at magnitude –1.5. This makes it nearly four times brighter than the next brightest star visible from mid-northern latitudes: Arcturus in the constellation Boötes. Sirius currently rises before 8 p.m. local time and ascends in the southeast throughout the evening hours.

The variable star Algol in Perseus reaches minimum brightness around 8:26 p.m. EST, when it shines at magnitude 3.4. If you start watching it after darkness falls, you can see it more than triple in brightness, to magnitude 2.1, over the course of about five hours. This eclipsing binary star runs through a cycle from minimum to maximum and back every 2.87 days. Algol appears in the eastern sky after sunset and passes nearly overhead around 9 p.m. local time.


Wednesday, December 26
Although Jupiter passed behind the Sun from our perspective just one month ago, it has already grown to prominence in the predawn sky. The giant planet rises nearly two hours before our star and climbs 10° high in the southeast 45 minutes before sunup. Gleaming at magnitude –1.8, it stands out nicely in the gathering dawn. A telescope shows Jupiter’s 32"-diameter disk, but you likely won’t see much detail because the light has to travel through thick layers of turbulent air near the horizon.

Pleiades
The Pleiades

The Pleiades star cluster (also known as the Seven Sisters) makes a wonderful target through binoculars on December evenings.

Terry Hancock
Thursday, December 27
Two of the finest deep-sky objects shine prominently on evenings in late December. The Pleiades and Hyades star clusters climb highest in the south during midevening but remain conspicuous nearly all night. The Pleiades, also known at the Seven Sisters and M45, appears like a small dipper to naked eyes. The larger Hyades forms the V-shaped head of Taurus the Bull. Although both look nice with naked eyes, binoculars show them best.

Friday, December 28
Mars continues to put on a nice show these December evenings. Look for the Red Planet halfway to the zenith in the southern sky as darkness falls. The world shines at magnitude 0.4 against the much dimmer stars of Aquarius the Water-bearer. A telescope reveals a disk that spans 8" and should show a few subtle surface features during moments of good seeing.

TheLastQuarterMoon
Last Quarter Moon

The Last Quarter Moon is a great target many evening-only observers never see because it rises around midnight local time. This 40-frame image shows great detail that just might inspire more early morning peeks at our nearest celestial neighbor.

David Barnett
Saturday, December 29
Last Quarter Moon occurs at 4:34 a.m. EST. You will see it poking above the eastern horizon around midnight local time and climbing highest in the south as twilight starts to paint the sky. The half-lit Moon spends the morning hours in the constellation Virgo the Maiden.

Sunday, December 30
Venus appears brilliant from the time it rises a little after 3:30 a.m. local time until close to sunrise more than three hours later. It stands about 25° above the southeastern horizon an hour before the Sun comes up. Gleaming at magnitude –4.6, the planet shines far brighter than all the other objects in the predawn sky except for the waning crescent Moon. When viewed through a telescope, Venus spans 27" and appears nearly halflit.

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