Full Moon arrives officially at 2:21 p.m. EST, but it will look completely illuminated all night. You can find it rising in the east at sunset and peaking high in the south shortly after midnight local time. It dips low in the west by the time morning twilight begins. The Moon spends the night near the border between the constellations Gemini the Twins and Cancer the Crab. If you live in the Eastern Hemisphere, look carefully and you should notice the dusky shading of a penumbral lunar eclipse over Luna’s southern half. The eclipse peaks at 19h10m UT, when 92 percent of the Moon lies within our planet’s light outer shadow.
Mercury reaches superior conjunction at 10 a.m. EST. This means the innermost planet lies on the opposite side of the Sun from Earth and remains hidden in our star’s glare. It will return to view in the evening sky late this month.
Saturday, January 11
Uranus reached opposition and peak visibility in late October, but it remains a tempting target in January. The outer planet appears highest in the south once darkness falls, when it stands two-thirds of the way to the zenith. The magnitude 5.8 world lies in southwestern Aries the Ram, near that constellation’s border with Pisces the Fish and Cetus the Whale. Although Uranus shines brightly enough to glimpse with the naked eye from a dark site, binoculars will help your search immensely. The closest guide star is magnitude 4.4 Xi1 (ξ1) Ceti, which lies 4° to the southeast. A telescope reveals Uranus’ disk, which spans 3.6″ and shows a distinct blue-green hue.
Sunday, January 12
The solar system’s brightest asteroid is 4 Vesta, and it is conveniently located high in the early evening sky among the background stars of Cetus the Whale. Vesta glows at magnitude 7.6, which makes it a reasonably easy target through binoculars from the country and a snap to see with a small telescope from the suburbs. This week offers prime viewing because the asteroid lies near 4th-magnitude Mu (μ) Ceti. Tonight, you can spot Vesta just 0.6° east of this star. No other object brighter than the asteroid resides in its immediate vicinity.
Monday, January 13
Mid-January finds several solar system objects lost in the Sun’s glare. Mercury, which passed on the far side of the Sun from our perspective three days ago, remains hidden from view. And today finds Saturn and the two brightest dwarf planets — Ceres and Pluto — in conjunction with our star. Pluto passes behind the Sun first, at 8 a.m. EST, with Saturn following two hours later and Ceres trailing three hours behind the ringed planet.
The Moon reaches perigee, the closest point in its orbit around Earth, at 3:21 p.m. EST. It then lies 227,396 miles (365,958 kilometers) away from us.
Tuesday, January 14
For those who recently caught the observing bug, the so-called Summer Triangle must seem like a huge misnomer. That’s because this asterism remains on view after darkness falls in January. Look for Vega, the fifth-brightest star in the sky and the brightest triangle member, low in the northwest. Deneb lies above Vega and about one-third of the way to the zenith. Deneb marks the top of another asterism, the Northern Cross, which stands nearly straight up from the horizon on January evenings. Altair, the third triangle member, scrapes the western horizon and sets shortly after 6:30 p.m. local time.
Venus gleams in the southwestern sky after sunset. The brilliant planet stands out just a half hour after sunset, when it appears 25° above the horizon, and remains on display until 8 p.m. local time. Shining at magnitude –4.0, it is by far the brightest point of light in the night sky. A telescope shows Venus’ disk, which spans 14″ and appears nearly 80 percent lit.
Thursday, January 16
The variable star Algol in Perseus reaches minimum brightness at 10:36 p.m. EST, when it shines at magnitude 3.4. If you start watching it during the midevening hours, 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 nearly overhead after darkness falls and dips toward the northwestern horizon well after midnight.
Last Quarter Moon occurs at 7:58 a.m. EST. You will see it poking above the eastern horizon just after midnight local time and climbing highest in the south as twilight starts to paint the sky. The half-lit Moon spends the morning hours among the background stars of Virgo the Maiden.
Mars passes 5° due north of Antares this morning. (Technically, the conjunction occurred at 11 p.m. EST yesterday, but the two objects don’t rise until around 4 a.m. local time.) Although the Red Planet officially lies in the southwestern corner of the constellation Ophiuchus, it appears in a single binocular field with Scorpius’ brightest star. Mars currently shines at magnitude 1.5, just 0.4 magnitude dimmer than Antares. That makes this morning a great opportunity 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.” Unfortunately, the view of the planet through a telescope proves disappointing — its disk spans only 5″ and shows no detail.
Saturday, January 18
If you’re game for a quick evening challenge, try to spot Neptune through binoculars. The distant planet lies 25° high in the southwest near the end of evening twilight and doesn’t set until 9 p.m. local time. The magnitude 7.9 world appears against the backdrop of Aquarius, 0.7° west-southwest of the 4th-magnitude star Phi (φ) Aquarii. You’ll need binoculars to spy Neptune and a telescope to see its blue-gray disk, which spans 2.2″.
Sunday, January 19
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 about a magnitude fainter than normal. Astronomers are still trying to figure out why this known variable star has dimmed to its faintest level in more than a century.