See what's up in the night sky for January 2021, including stargazing events and the moon's phases, in this Space.com gallery courtesy of Starry Night Software.
Saturday, January 2—Earth at Perihelion (at 14:00 GMT)
On Sunday, January 5, the Earth will reach perihelion, its minimum distance from the sun for the year. At that time Earth will sit 91.399 million miles (147.093 million km) from our star—or 1.67% closer than our mean distance of 1.0 Astronomical Units. As winter-chilled Northern Hemisphere dwellers will attest, daily temperatures on Earth are not controlled by our proximity to the sun, but by the number of hours of daylight we experience.
Sunday, January 3—Quadrantids Meteor Shower Peak (before dawn)
Named for a now-defunct constellation called the Mural Quadrant, the annual Quadrantids meteor shower runs from December 30 to January 12. This shower's most intense period, when 50 to 100 meteors per hour can occur, lasts only about 6 hours surrounding the peak, which is predicted to occur on Sunday, January 3 at 10:00 GMT (or 5 a.m. Eastern time). At that time, the Earth will be traversing the thickest part of the debris field. Quadrantids commonly produce bright fireballs owing to the shower's source, an asteroid designated 2003EH. The best time for viewing Quadrantids will be before dawn, when the shower's radiant, which lies beyond the tip of the Big Dipper's handle, will be high in the northeastern sky. Unfortunately, a bright moon will greatly reduce the number of Quadrantids meteors in 2021.
Monday, January 4—Moon meets Asteroid Vesta (post-midnight)
In the southwestern sky on Monday, January 4, the waning gibbous moon will pass near the main belt asteroid designated (4) Vesta. After the moon rises late on Sunday evening, magnitude 7.1 Vesta will be sitting several finger widths below (or 4 degrees to the celestial east) of the moon. Over the rest of the night, the moon's orbital motion will carry it half as far from Vesta, and the diurnal rotation of the sky will lift the asteroid above the moon. The two objects will fit together in the field of view of binoculars (red circle).
Wednesday, January 6—Third Quarter Moon (at 9:37 GMT)
When the moon reaches its third quarter phase at 9:37 GMT (or 2:37 a.m. EST) on Wednesday, January 6, it will rise at about midnight, and then remain visible in the southern sky all morning. At third, or last, quarter the moon is illuminated on its western side, towards the pre-dawn Sun. Third quarter moons are positioned ahead of the Earth in our trip around the Sun. About 3½ hours later, Earth will occupy that same location in space. The week of dark, moonless evening skies that follow this phase will be ideal for observing deep sky targets.
Saturday, January 9—Mercury below Jupiter and Saturn (post-sunset)
From January 9 to 12, the planet Mercury will climb past the gas giants Jupiter and Saturn, which will be descending sunward. After sunset, look just above the southwestern horizon after sunset on Saturday, January 9 to see Mercury sitting just a thumb's width to the lower left (or 1.7 degrees to the celestial south) of Saturn—with brighter Jupiter positioned above them. All three objects will fit within the field of view of binoculars (red circle). Mercury and Saturn will be a challenge to see within the evening twilight – except for skywatchers at southerly latitudes, where the sky will darken faster. The orbital motion (red arc) of Mercury will be carrying the speedy planet between Earth and the sun, while the gas giants will be on the far side of our star.
Sunday, January 10—Jupiter, Saturn, & Mercury in a 2.3° Circle (post-sunset)
Mercury will continue to move past Jupiter and Saturn on Sunday, January 10. After 24 hours, the speedy planet will be higher – forming a small triangle just above the southwestern horizon with Saturn 2 degrees to Mercury's right and Jupiter positioned 2 degrees above them. Mercury and Saturn will be a challenge to see within the evening twilight. The trio will easily fit into the field of view of binoculars (red circle) – but ensure that the sun has completely vanished below the horizon before using them. The three planets will set at about 6 p.m. local time, an hour after sunset.
Monday, January 11—Mercury meets Jupiter (after sunset)
On Monday, January 11, Mercury's orbital motion (red curve) will lift the planet a thumb's width to the lower left (or 1.5 degrees to the celestial south) of bright Jupiter – with dimmer Saturn two fingers widths to their lower right (celestial west). Use brighter Jupiter to find dimmer Mercury and Saturn. They'll be a challenge to see within the evening twilight. The best viewing time will be around 5:20 p.m. local time – but you'll need an unobstructed view to the southwest. You can try to see the planet grouping again on Tuesday, when Mercury will be to Jupiter's upper left.
Monday, January 11—Old Moon visits Venus (pre-dawn)
Low in the southeastern sky on Monday, January 11, the delicate crescent of the old moon will sit a few finger widths to the right (or 4 degrees to the celestial southwest) of the bright planet Venus. The pair, which will rise at about 6:40 a.m. in your local time zone, should remain easily visible while the morning sky brightens towards sunrise, making a nice photo opportunity when composed with some interesting scenery.
Wednesday, January 13—New Moon (at 5:00 GMT)
At 5:00 GMT on Wednesday, January 13, the moon will officially reach its new moon phase. When new, the moon is traveling between Earth and the Sun. Since sunlight can only reach the far side of the moon, and the moon is in the same region of the sky as the sun, the moon becomes completely hidden from view for about a day.
Thursday, January 14—Crescent Moon near Jupiter and Mercury (after sunset)
Three evenings after Mercury passes close to bright Jupiter in the southwestern sky, a pretty young crescent moon will join those two planets immediately after sunset on Thursday, January 14 – setting up a lovely photo opportunity. The moon will be positioned a fist's diameter to the upper left (or 10 degrees to the celestial southeast) of Jupiter, with dimmer Mercury midway between them. You'll need an unobstructed southwestern horizon to catch Jupiter before it sets at 6 p.m. in your local time zone. Mercury will become easier to see just before it sets at 6:18 p.m., and then the moon will drop below the horizon at 6:35 p.m.
Thursday, January 14—Uranus Stands Still (evening)
On Thursday, January 14, the distant, blue-green planet Uranus will temporarily cease its motion through the distant stars of southwestern Aries—completing a westward retrograde loop that began in mid-August (red path with labelled dates:times). After Thursday, the planet will begin to move eastward again. At magnitude +5.75, Uranus can be seen in binoculars (red circle) and backyard telescopes, and even with unaided eyes, under dark skies. Mars can help you find it. In mid-evening the bright red planet will be positioned three finger widths to the lower right (or 3.25 degrees to the celestial northwest) of Uranus.
Saturday, January 16—The Pleiades (all night)
At about 8:30 p.m. local time on mid-January evenings, the Pleiades open star cluster, also known as the Seven Sisters and Messier 45 is positioned high in the southern sky. The rest of its home constellation Taurus, the Bull sits below the cluster. Visually, the cluster is composed of medium-bright, hot blue stars named Asterope, Merope, Electra, Maia, Taygeta, Celaeno, and Alcyone. In Greek mythology, those characters were the daughters of Atlas, and half sisters of the Hyades. They are indeed related – recently born of the same primordial gas cloud. To the naked eye, only six of the sister stars are usually apparent; their parents Atlas and Pleione are huddled together at the east end of the grouping. Under magnification, hundreds of stars appear. Not surprisingly, many cultures, including Aztec, Maori, Sioux, Hindu, and more, have noted this object and developed stories around it. In Japan, it is called Suburu, and forms the logo of the eponymous car maker. Due to its shape, the Pleiades are sometimes confused with the Little Dipper.
Wednesday, January 20—First Quarter Moon (at 21:01 GMT)
When the moon completes the first quarter of its orbit around Earth at 4:01 p.m. EST (or 21:01 GMT) on Wednesday, January 20, the relative positions of the Earth, sun, and moon will cause us to see it half-illuminated—on its eastern side. At first quarter, the moon always rises around noon and sets around midnight, so it is also visible in the afternoon daytime sky. The evenings surrounding first quarter are the best for seeing the lunar terrain when it is dramatically lit by low-angled sunlight.
Wednesday, January 20—Moon Mars and Uranus (evening)
In the southwestern sky on the evening of Wednesday, January 20, the waxing, half-illuminated moon will pass Mars and Uranus, which will be reaching their minimum separation that night. After dusk the moon will be positioned a palm's width below (or 7 degrees to the celestial southwest of) bright Mars – with much dimmer Uranus sitting a thumb's width below (or 1.6 degrees south of) the reddish planet. By the time Mars sets in the west after midnight local time, the diurnal rotation of the sky will slide the moon to the planets' lower left.
Thursday, January 21—The Lunar Straight Wall (evening)
On Monday evening, November 23, the pole-to-pole terminator boundary that divides the lit and dark hemispheres of the waxing gibbous moon, will fall just to the left (or lunar west) of Rupes Recta, also known as the Lunar Straight Wall. This feature is very obvious in good binoculars and backyard telescopes. The rupes, Latin for "cliff", is a north-south aligned fault scarp that extends for 65 miles (110 km) across the southeastern part of Mare Nubium—that's the large dark region in the lower third of the moon's Earth-facing hemisphere. The Straight Wall is always prominent a day or two after first quarter, and again just before third quarter. For reference, the prominent crater Tycho is located due south of the Straight Wall.
Saturday, January 23—Vesta Stands Still (overnight)
On Saturday, January 23, the large main belt asteroid designated (4) Vesta will begin a westward retrograde loop (red path with dates) through the stars of Leo. The loop will continue through its April 4 opposition, and into late April. Tonight, magnitude 6.65 Vesta can be found sitting several finger widths to the right (or 4.25 degrees to the celestial south) of the bright star Denebola, the lion's tail. Vesta will cross the southern sky during the bulk of the night.
Saturday, January 23—Mercury at Greatest Eastern Elongation (evening)
In the west-southwestern sky on the evening of Saturday, January 23, Mercury (orbit shown in red) will reach its widest separation, 19 degrees east of the Sun. With Mercury positioned close to the evening ecliptic (green line), this appearance of the planet will offer excellent views for Northern Hemisphere observers, but it will not be ideal for observers in the Southern Hemisphere. The optimal viewing times at mid-northern latitudes fall around 6 p.m. local time. Viewed in a telescope (inset) the planet will exhibit a waning, half-illuminated phase.
Monday, January 25—Bright Moon beside Messier 35 (all night)
Once the sky darkens on Monday evening, January 25, skywatchers can look for the large open star cluster known as Messier 35, or the Shoe-Buckle Cluster, sitting just to the upper right (or celestial west) of the bright waxing gibbous moon in Gemini. During the night the moon's orbital motion (green line) will draw the moon farther from the cluster, and the diurnal rotation of the sky will lift the moon higher compared to the cluster. To best see Messier 35's stars, hide the bright moon beyond the left edge of your binoculars' field of view.
Thursday, January 28—Full Wolf Moon (at 19:16 GMT)
The January full moon will occur at 2:16 p.m. EST (or 19:16 GMT) on Thursday, January 28. Known as the Wolf Moon, Old Moon, and Moon after Yule, this moon always shines in or near the stars of Gemini or Cancer. Since it's opposite the sun on this day of the lunar month, the moon is fully illuminated, and rises at sunset and sets at sunrise. Full moons during the winter months reach as high in the sky as the summer noonday sun, and cast similar shadows.
Friday, January 29—Full Moon Occults Eta Leonis (approx. 3:09 to 4:20 GMT)
In late evening on Friday, January 29, observers across the southern half of the continental USA, Mexico, Central America, and northern South America can see the waning full moon pass in front of (or occult) the bright, magnitude 3.45 star Eta Leonis (η Leo). Regions to the north and south will see the moon pass very close to that star. The ingress and egress times vary by location on Earth, so use a planetarium app like Starry Night to look up the times for your location. In Miami, the bottom, lit limb of the moon will cover the star at 10:09 p.m. EST. The star will re-appear from behind the upper, dark edge of the moon at 11:20 p.m. EST. Those times convert to 3:09 to 4:20 GMT on January 30). The event will be observable in binoculars and backyard telescopes – but remember that a telescope (red circle) will likely invert and/or mirror the scene shown here.