For the first half of January, magnitude -0.7 Mercury will be visible in the southwestern sky after sunset. In the first few days of the month, it will be poised to the upper left (or celestial southeast) of much brighter Venus. Mercury’s greatest elongation, 19 degrees east of the Sun, will occur on January 7, a week before its perihelion. This is a brief and reasonably good apparition for Northern Hemisphere observers, but a less ideal one for southerners. The best viewing time around elongation will be 5:30 p.m. local time. Mercury will approach Saturn until the pair closes to within 3.4 degrees of one another on January 12-13. After that, Mercury’s westerly retrograde motion will outpace Saturn in their race sunward. Mercury will rapidly become lost in the twilight after mid-month. Telescope views will reveal a waning phase that decreases from 76-per-cent to a thin crescent. Meanwhile, the planet’s apparent disk size will swell from 6 arcseconds to nearly 10 arcseconds. (Always ensure that the Sun is completely below the horizon before training optics on Mercury.) The very young crescent Moon might be spotted less than 5 degrees below (south of) Mercury on January 3. But the Moon will be more easily seen on the following evening, when it will sit 11 degrees to Mercury’s upper left. Following inferior solar conjunction on January 26, Mercury will enter the east-southeastern pre-dawn sky, commencing a lengthy, but poor apparition for northerners.
The opening few days of January will find Venus low in the west-southwestern sky after sunset, and rapidly descending sunward. When Venus reaches inferior conjunction on January 8-9, our sister planet will be closer than any planet has been to Earth in a century — a mere 0.266 Astronomical Units, 39.767 million kilometres or 133 light-seconds. Telescope views of the planet will be very risky while it’s that close to the Sun. Experienced observers might glimpse Venus’ razor-thin crescent and its swollen apparent disk diameter of 63 arcseconds! Venus will spend all of January moving retrograde westward through northern Sagittarius. When the planet re-appears in the east-southeastern pre-dawn sky several mornings after conjunction, it will rapidly climb out of the morning twilight and steadily brighten. Venus will end January at magnitude -4.8, and preparing to pass a half-dozen degrees to the north of Mars during early February. The old crescent Moon will share the pre-dawn sky with Venus on January 29 and 30.
During January, Mars will be observable in the southeastern pre-dawn sky while it slowly climbs away from the Sun on its year-long journey to opposition in late December. On January 1, the ruddy, magnitude 1.53 planet will rise among the stars of Ophiuchus after 5 a.m. local time — just five degrees northeast of its rival, the bright star Antares. Over the course of the month, Mars will grow in apparent diameter from 4 to 4.3 arcseconds and brighten a little to magnitude 1.4. Mars’ easterly prograde motion will hold it in place while the background stars migrate west. On January 20 the red planet will pass into the rich star fields of Sagittarius. Mars will pass telescope-close to the globular cluster NGC 6235 on January 3, the planetary nebula IC 4634 on January 6, globular NGC 6287 on January 7, the Ghost of Mars Nebula (NGC 6369) on January 15, and the globular NGC 6401 on January 18. On January 26, Mars will pass less than 1.5 degrees to the SSW of the Trifid Nebula (Messier 20) and the nearby open star cluster Messier 21. That same morning, the Lagoon Nebula (Messier 8) with its central star cluster NGC 6530 will be positioned just 0.5 degree to the south of Mars. Toward month’s end, Mars will greet much brighter Venus, which will approach from Mars’ upper left (or celestial northeast). On January 29, the slender crescent of the old Moon will shine several degrees to the south of Mars, making a nice photo opportunity. The magnitude 7.6 asteroid designated (4) Vesta will be nearby, too — about 6.5 degrees to the east-northeast of Mars.
Our time for viewing Jupiter will conclude during January. During the first half of the month the bright, magnitude -2.1 planet will be easily observed in telescopes in early evening as it moves prograde eastward through central Aquarius in the southwestern sky. But Jupiter will be flirting with the evening twilight by month’s end — its angle from the Sun will have been reduced to only 25 degrees. Jupiter’s four Galilean moons will appear on either side the planet in binoculars. In telescopes, the Great Red Spot will cross Jupiter’s disk every second or third night. Thirteen times fainter Saturn will shine 18 degrees to the lower right (celestial west) of Jupiter, until the ringed planet disappears into the twilight towards month-end. On January 5, the waxing crescent Moon will pass 6 degrees to the southwest of Jupiter.
During early evening for the first week of January, Saturn will be observable in the west-southwestern sky as it moves eastward among the stars of central Capricornus. After mid-month, Saturn will become increasingly swamped by twilight. The ringed planet’s distance from Mercury, which will be sitting to its lower right (or celestial west), will decrease to 3.4 degrees on January 12-13. After that encounter, Mercury’s westerly retrograde motion will outpace Saturn as they both swing sunward. The young crescent Moon will shine 5 degrees to Saturn’s left on January 4.
Magnitude 5.7 Uranus will be observable in binoculars and telescopes all evening long during January. Its small, blue-green dot will be moving slowly retrograde westwards in southern Aries, 10.5 degrees southeast of that constellation’s brightest stars, Hamal and Sheratan, and only 5 degrees from the medium-bright star Mu Ceti to its south. The planet will most visible when it climbs to its highest position in the southern sky at around 7 p.m. local time. From January 10 to 11, the bright, waxing gibbous Moon will hop past Uranus.
The distant and blue-coloured planet Neptune will be observable in the southwestern sky in early evening during January. The magnitude 7.9 planet will be traveling very slowly eastward among the stars of northeastern Aquarius. If the sky is very dark, Neptune can be seen in binoculars. To locate it, find the north-south grouping of five medium-bright stars Psi, Chi, and Phi Aquarii (or ψ, X, and φ Aqr). Neptune’s non-twinkling speck will sit 3 degrees to the north-northeast of the top star, Phi. Viewed in a telescope, Neptune’s apparent disk size will be 2.25 arcseconds.
Chris Vaughan is a science writer, geophysicist, astronomer, planetary scientist and an “outreach RASCal.” He writes Astronomy Skylights, and you can follow him on Twitter at @astrogeoguy. He can also bring his Digital Starlab portable inflatable planetarium to your school or other daytime or evening event. Contact him through AstroGeo.ca to tour the Universe together.