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The Sky This Week from January 17 to 26

While a crescent Moon passes near three planets this week, Venus has a rare close meeting with Neptune.
OrionSiriusCanopus
Orion and Sirius
Jagged, tooth-shaped ice structures known as penitentes dominate the high-altitude hills of Chile’s Atacama Desert in the foreground of this image. In the sky above, the familiar constellation Orion the Hunter stands at center with the night sky’s brightest star, Sirius, to its lower right. The sky’s second-brightest star, Canopus, appears farther to the right.
ESO/Babak Tafreshi
Friday, January 17
Last Quarter Moon occurs at 7:58 a.m. EST. By the time it rises shortly after 1 a.m. local time Saturday morning, it will appear slightly but noticeably less than half-lit. The Moon then lies near the border between the constellations Virgo the Maiden and Libra the Scales.

Saturday, January 18
One of the sky’s most familiar constellations rules January’s sky from dusk until near dawn. Orion the Hunter appears conspicuous in the southeast after darkness falls and climbs highest in the south around 10 p.m. local time. It then stands about halfway to the zenith from mid-northern latitudes. If you’ve watched Orion over the years, you might notice that it doesn’t look quite the same now. Ruddy Betelgeuse, which marks one of the Hunter’s shoulders, currently glows near magnitude 1.5. This is about a magnitude fainter than usual and noticeably dimmer that Aldebaran in neighboring Taurus, a star that Betelgeuse normally beats handily. Astronomers are still trying to figure out why this known variable star has dimmed to its faintest level in more than a century.

Sunday, January 19
The variable star Algol in Perseus reaches minimum brightness at 7:25 p.m. EST, when it shines at magnitude 3.4. If you start viewing as soon as darkness falls, you can watch 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 nearly overhead after sunset and sinks low in the northwest well after midnight.

Monday, January 20
Mars passed 5° due north of Antares three days ago, and the planet and star remain separated by the same distance this morning, with Mars now lying north-northeast of Antares. The pair rises around 4 a.m. local time, about a half-hour after the waning crescent Moon. The three objects make a lovely sight in the southeastern sky before dawn, with Mars about 4° directly below the Moon and Antares 7° to Luna’s lower right. Mars shines at magnitude 1.5, just 0.4 magnitude dimmer than Antares. Take a few moments to compare the colors of the two objects, and come to understand why ancient observers named the star Antares, which literally means “rival of Mars.”

Pleiadesfor117STW
The Pleiades star cluster
The dipper-shaped Pleiades (M45) appears high in the south early on January evenings. At a distance of 440 light-years, the Pleiades ranks as the closest object in Charles Messier’s famous catalog.
Jamie Cooper
Tuesday, January 21
Two of the finest deep-sky objects shine prominently on January evenings. The Pleiades and Hyades star clusters appear highest in the south in early evening but remain conspicuous until well past midnight. The Pleiades, also known at the Seven Sisters and M45, looks like a small dipper to the naked eye. The larger Hyades forms the V-shaped head of Taurus the Bull. Both look nice without optical aid, but binoculars show them best.

Wednesday, January 22
Although Jupiter passed on the far side of the Sun from Earth less than a month ago, it returns to view in morning twilight this week. Use the waning crescent Moon as a guide this morning. The Moon rises around 5:30 a.m. local time, followed a half-hour later by the giant planet. Magnitude –1.9 Jupiter climbs 4° high 45 minutes before sunrise, when the two objects make a gorgeous sight against the twilight glow.

Thursday, January 23
Venus gleams in the southwestern sky after sunset. The brilliant planet stands out just a half hour after sunset, when it appears nearly 30° above the horizon, and remains on display until after 8 p.m. local time. Shining at magnitude –4.1, it is by far the brightest point of light in the night sky. A telescope shows Venus’ disk, which spans 15" and appears three-quarters lit.

Friday, January 24
The brightest star in the night sky puts on a nice show January evenings. Gleaming at magnitude –1.5, Sirius shines nearly four times brighter than the next brightest star visible from mid-northern latitudes: Arcturus in the constellation Boötes. (Although Venus shines some 10 times brighter.) Sirius rises shortly after sunset and climbs highest in the south by late evening.

New Moon occurs at 4:42 p.m. EST. At its New phase, the Moon crosses the sky with the Sun and so remains hidden in our star’s glare.

MoonMercury
The Moon passes Mercury
A waxing crescent Moon passes near Mercury in bright twilight the evening of January 25. A similar scene occurred January 31, 2014, when this photographer captured the two solar system objects. (The planet appears as a bright dot at upper left.)
Gilbert Ahlstrand
Saturday, January 25
Mercury returns to the evening sky late this week. If you have a sharp eye, a clear sky, and an unobstructed horizon toward the west-southwest, you should be able to glimpse it through binoculars. For observers at mid-northern latitudes, it lies just 2° high 30 minutes after the Sun goes down tonight. Fortunately, you’ll have some help spotting it: A wafer-thin crescent Moon appears just 2° to the left of the magnitude –1.1 planet. You’ll have only about 10 minutes to catch them before they sink out of sight.

Sunday, January 26
This evening, Venus serves as a guide to the solar system’s outermost major planet, Neptune. Because the distant world glows feebly at magnitude 7.9, you’ll need binoculars or a telescope to spot it. Once the sky grows dark about 90 minutes after sunset, target Venus with binoculars or a telescope at low power. Note the 4th-magnitude star Phi (φ) Aquarii 1.4° above it. Neptune lies two-thirds of the way from Venus to Phi. Don’t confuse the outer planet with a slightly brighter star that stands 0.5° to its right. Through a telescope, Venus appears 15" across and three-quarters illuminated while Neptune shows a 2.2"-diameter disk colored blue-gray. If clouds interfere this evening, don’t despair — the two planets will appear even closer to each other tomorrow night.

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