Skylights: January 2023

On January 4, at about 4:00pm EST, Earth is as close to the Sun as it will be all year. Known as perihelion, we’ll be just 0.983296 AU from the Sun. Compared with aphelion, which occurs on July 6, we will be 0.033385 AU, or 3.29% closer. That’s a difference of 5 million kilometers, 13 times the distance to the Moon, and 16.66 light seconds.

The latest sunrise of the year occurs at 7:14am on the 4th. We won’t see the Sun rise before 7:00am until the final day of January, which is also the last day that the Sun sets before 5:00pm. Transiting Sagittarius through the beginning of the month, the Sun crosses into Capricornus on the 20th.

Mercury is visible low in the southwestern sky on the 1st of the month, but it quickly moves towards inferior conjunction on the 7th, then becomes visible in the southeast before sunrise, the last favorable morning apparition of the innermost planet until September. Find Mercury 3° north-northeast of the globular cluster Messier 22 in Sagittarius on the 23th, and on the 28th, the two objects are equal in elevation over the southeastern horizon, with Mercury appearing 3.8° to the left of the cluster.

During the last week of January, Mercury rises 90 minutes before the Sun, and the planet reaches its greatest elongation, 25° west of the Sun, on the 30th.

Venus is now coming into good view in the early evening sky, where its unmistakable brilliance gives it its nickname the Evening Star. It crosses into Capricornus on the 2nd, where it will spend the next three weeks, before becoming a resident of Aquarius. Venus climbs higher over the southwestern horizon each night as it moves eastward, closer to Saturn. The two planets are in conjunction, just 0.3° apart, on the 22nd. On the following evening, the 2.4-day waxing crescent Moon appears in a line with the two planets, about 7° to the east.

Telescopically, Venus will not appear as anything more than a brilliant white disc just over 10 arcseconds across, but as it climbs higher over the horizon, it presents keen observers with a challenge of determining the earliest date that its gibbous shape can be discerned. 

Mars reaches its stationary point on the 12th, so it appears to be not moving significantly until later in the month, after it resumes its prograde (eastward) motion. It resides in Taurus, just 1.5° north of the Davis’s Dog asterism, an oft-overlooked grouping of 5th-6th magnitude stars located within the same binocular field of view as the more prominent Hyades.

Earth is rapidly retreating from Mars, causing the Red Planet to dim and shrink noticeably during January. By month’s end, it will be just 12 arcseconds, and begin to once again show a distinct gibbous phase.

Although dimming, Mars still shines as bright as many of the members of the Winter Hexagon, giving a temporary, altered appearance to our winter sky’s most prominent asterism. The waxing gibbous Moon is 1.8° E of Mars on the 3rd, and 0.2° south of the Red Planet on the 31st.

January is the last month to view Saturn in the evening sky before it moves into conjunction next month. Last summer you may recall that it formed an equilateral triangle with the stars Deneb Algedi and Nashira (delta and eta Capricorni), but moved out of position as it went through its retrograde motion. Having returned to prograde (eastward) motion, it once again moves past these two stars, and forms the equilateral triangle with them on the 6th. 

Jupiter crosses north of the celestial equator for the first time since 2016 on January 13th. It will remain in the celestial northern hemisphere until 2028.

On the evening of the 25th, the 4.7-day crescent Moon lies 2.1° to the east-southeast of Jupiter, just before the two objects set in the west.

January is the last opportunity to view Saturn in the evening sky. After its meeting with Venus on the 22nd, it sinks deeper into twilight as it approaches conjunction in mid-February.

Uranus is occulted by the 9-day old gibbous Moon on the 1st. Ingress, which occurs at 3:33pm in the afternoon, occurs during daylight hours. Egress from the illuminated limb of the Moon, just beyond the southern edge of Mare Smythii, occurs at 4:39pm, which although still during civil twilight, should be visible through a large telescope with high magnification.

For the remainder of January, Uranus is well-paced for observation high in the south during the early evening hours. Its distant, magnitude 5.7 blue-green glow can be detected with binoculars when bright moonlight is not interfering, or even with the unaided eye from an exceptionally dark locale, just over halfway between Hamal (alpha Arietis), and omicron Tauri. Uranus reaches its stationary point on the 18th, and resumes prograde (eastward) motion thereafter.

Neptune, shining at magnitude 7.8 just 10° west-southwest of Jupiter, is best seen in the early evening hours, as it will set before 9:00pm by month’s end.

Pluto is in conjunction on the 18th.

The Full Wolf Moon occurs early in the evening on the 6th. As we’re still within a half-month of solstice, the Moon is located near the most northerly portion of the ecliptic, and, in fact, is a few degrees north of the ecliptic, so this is once again one of the highest full Moons of the year, transiting at an elevation of 74.6° a few minutes after midnight on the 7th.

The Moon is last quarter on the 14th, new on the 21st, and first quarter on the 28th.

Asteroid 2 Pallas reaches opposition on the 2nd, in the southerly portion of Canis Major. At a declination of -32°, the magnitude 7.7 asteroid could present a challenge to observers due to its location, but it moves north as it reaches its closest point to Earth, 1.413 AU, on the 14th. It remains an 8th magnitude object as it passes north of Sirius later in February.

Dwarf planet Ceres spends January near the Realm of the Galaxies in Virgo. On the 20th, the 8th magnitude asteroid passes rho Virginis, and over the final two weeks of January, within 2° of the galaxy M60.

For the first time since Comet NEOWISE in 2020, the northern sky has a bright comet worth watching. C/2022 E3 ZTF, discovered by the Zwicky Transient Facility, a sky survey running from the historic 48” Schmidt telescope at Palomar. The comet reaches perihelion on January 14, and is closest to Earth on February 2 at 0.29 AU.

C/2022 E3 ZTF begins the year in the morning sky, rapidly approaching from within Corona Borealis, but goes circumpolar from January 19 through February 6, during which time it is expected to become as bright as fifth magnitude