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Totality over America

The orange glow from all Earth’s sunrises and sunsets painted the Moon during the September 28, 2015, total lunar eclipse. Observers across the Americas should get a similar view the night of January 20/21.
José J. Chambó

A total eclipse of the Moon is a highlight in a month that also features exceptional views of several planets. While the fainter worlds gather in the early evening sky, the more luminous ones congregate before dawn. Skywatchers should mark their calendars for the morning of the 22nd, when the two brightest planets, Venus and Jupiter, pass just 2° from each other.

Let’s begin our tour of the night sky with its top event: the total lunar eclipse. Observers under a clear sky across North and South America can watch the Full Moon fade and change color as it slides through Earth’s shadow the night of January 20/21.

The eclipse gets underway the evening of the 20th. Luna enters our planet’s outer penumbral shadow at 9:37 p.m. EST. The penumbra’s subtle shading initially has little effect on the Moon, but viewers should see the lower limb start to darken within a half-hour.

The partial eclipse officially begins at 10:34 p.m., when our satellite encounters Earth’s inner umbral shadow. No direct sunlight enters the umbra, so you might expect the shadow to look black. And it does, at least at first. But as the Moon dives deeper into the shadow and totality approaches, it takes on a distinct orange glow. The color comes from all Earth’s sunrises and sunsets — our planet’s atmosphere bends this light into the shadow.

The color becomes even more noticeable during the 62 minutes of totality, which commences at 11:41 p.m. The eclipsed Moon is mesmerizing however you view it, but be sure to enjoy the surrounding sky. As the eclipse progresses, the sky darkens and the star-studded winter sky blossoms into view. Binoculars will reveal the attractive Beehive star cluster (M44) just 7° east of the Moon.

The total phase of the eclipse ends at 12:43 a.m., and the Moon exits the umbral shadow at 1:51 a.m. The final trace of the penumbra leaves the lunar disk without fanfare at 2:48 a.m. Don’t pass up the opportunity to see this total lunar eclipse — you’ll have to wait until May 2021 for the next one.

While the Moon glows orange only one evening this month, Mars shows a similar color every January night. The planet appears about halfway to the zenith in the southwest as darkness falls. It remains on view until it dips below the western horizon after 11 p.m. local time.


The eclipsed Moon hangs just below the twin stars Castor and Pollux in Gemini at midtotality January 20/21.

All illustrations: Astronomy: Roen Kelly
Mars stands out against the relatively dim background stars of Pisces the Fish. It shines at magnitude 0.5 in early January and fades to magnitude 0.9 by month’s end, though that’s still more than 10 times brighter than any of the constellation’s stars.

The planet begins the month southeast of Pisces’ Circlet asterism, a distinctive grouping that lies due south of the Great Square of Pegasus. The ruddy world then treks eastward rapidly. It slides 0.9° south of 4th-magnitude Epsilon (ε) Piscium on January 26.

Despite Mars’ prominence to the naked eye, it doesn’t offer much to observers with telescopes. The planet continues to move away from Earth and thus shrink in size. Its apparent diameter holds at 7" during the first half of January but drops to 6" by month’s close. You’ll need excellent viewing conditions to see it as anything more than a featureless disk.

Mars serves as a guide to finding Uranus and Neptune this month. The two conveniently bracket the Red Planet and glow brightly enough to show up through binoculars.

You’ll want to hunt for Neptune first. It lies west of Mars and thus hangs lower in January’s evening sky. The outer world lurks among the background stars of Aquarius, standing some 30° high at the end of twilight in early January. Its altitude drops by half at the end of the month, however, so don’t put off your attempts to track it down.

Neptune lies midway between Lambda (λ) and Phi (ϕ) Aquarii, a pair of 4th-magnitude stars in eastern Aquarius. A trio of 5th- and 6th-magnitude stars — 81, 82, and 83 Aqr — form a right triangle in this area. But you’ll need to hold your binoculars steady to spot the magnitude 7.9 planet among these stars.

Neptune lies 14' southeast of 81 Aqr on January 1. But the ice giant moves eastward and pulls away from 81. It ends the month 55' east of this star and 46' north of 83 Aqr.

Venus and Jupiter pass 2° from each other January 22. The two were just as close when they appeared above Tibet’s Potala Palace in July 2015
Jeff Dai
A few other stars closer to Neptune’s brightness populate this region, so it can be tricky to confirm a sighting. The best way is to target your suspected planet through a telescope. Only Neptune shows a distinct disk that spans 2.2" and displays a subtle blue-gray color.

You’ll have an easier time chasing down Uranus. Not only does it shine brighter than Neptune (magnitude 5.8), but it also stands higher in the evening sky. Uranus spends the month in eastern Pisces, just a stone’s throw from that constellation’s border with Aries. The planet appears 60° above the southern horizon as twilight fades to darkness in early January, and it’s still 50° high in the southwest at the same time late this month.

Uranus’ position relative to the background stars barely budges during the first half of January. Look for it 1.2° north of the 4th-magnitude star Omicron (ο) Piscium. The planet edges eastward during the month’s second half, reaching a point 1.4° north-northeast of Omicron by the 31st. Because no other star in the vicinity glows as brightly as Uranus, you should be able to identify it quite easily.

If you’re still unsure which point of light is the planet, point a telescope in its direction. Uranus displays a disk that measures 3.6" across and appears distinctly blue-green.

Once Uranus sets after midnight, the sky remains planet-free for a few hours. But don’t go to sleep yet — or at least, plan to wake up early to catch the best January has to offer.

New Year’s Day dawns in spectacular fashion, with a waning crescent Moon and three bright planets arrayed above the southeastern horizon. The Moon rises first, just after 3 a.m. local time, with Venus following a half-hour later. Five degrees separate the night sky’s two brightest objects. Jupiter comes up about 90 minutes after Venus and Mercury trails an hour later.

A half-hour before sunup, the four solar system objects stretch out across 35° of sky. Venus appears nearly 30° high and shines at magnitude –4.6; Jupiter is 15° high and glows at magnitude –1.8; and magnitude –0.4 Mercury stands 5° high in the brightening twilight. You also might catch a glimpse of the 1st-magnitude star Antares 5° to Jupiter’s lower right.

Earth’s neighboring planet shines brilliantly high in the southeast when it reaches greatest elongation from the Sun during January’s first week.
Over the next three days, the Moon glides past the morning planets. On the 3rd, Luna appears 4° to Jupiter’s left, and the following morning, an even thinner crescent hangs 3° above Mercury.

Venus reaches greatest elongation January 5/6, when it lies 47° west of the Sun and climbs 25° high in the southeast an hour before sunrise. If you point a telescope at the planet on the 6th, you’ll see a 25"-diameter disk that should appear half-lit. But it probably won’t — Venus’ phase always appears as a fat crescent when it should be half-lit. German astronomer Johann Schröter first described this effect in 1793, which likely arises from the planet’s thick atmosphere. Observers typically see Venus as 50 percent illuminated a few days after greatest elongation. What do you find?

Each day after greatest elongation, Venus loses a bit of altitude while Jupiter climbs higher. The two are destined for a stunning conjunction January 22, when Venus passes 2° north of Jupiter. The pair rises in a dark sky by 4:30 a.m. local time and remains visible even in bright twilight.

A waning crescent Moon returns to the predawn sky at month’s end. On January 30, it appears 6° to Jupiter’s upper right; the following morning, it slides 2° to Venus’ right.

Mercury has long since disappeared by then. The innermost planet adorns the twilight sky during January’s first week, but the Sun’s glare soon overwhelms it. It passes behind the Sun on January 29.

Although Saturn passes on the far side of the Sun on January 1/2, it emerges in the predawn sky during the month’s second half. On the 31st, the ringed world stands 7° high in the southeast 45 minutes before sunrise. You should be able to spot the magnitude 0.6 planet through binoculars, though you’ll want to wait until next month to target it with a telescope.

Observers in southwestern Alaska, Japan, and eastern Asia who practice safe solar-viewing techniques can see the Moon partially eclipse the Sun on January 5/6. Maximum eclipse occurs in eastern Siberia, where our satellite covers 71 percent of the Sun’s disk.

This wide lunar valley formed from debris blasted out by the impact that created Mare Nectaris.
Consolidated Lunar Atlas/UA/LPL; inset: NASA/GSFC/ASU

When second best is still fine

Only about a dozen major lunar valleys appear on the Moon’s nearside. Most observers consider Vallis Alpes (Alpine Valley) in the north to be the best, but Vallis Rheita (Rheita Valley) in the southeast runs a close second.

The two are a study in contrasts. The Alpine Valley arose when the lunar crust pulled apart and the land collapsed. The Rheita Valley formed as a line of overlapping craters. The impacts occurred in rapid succession, with each new one obliterating the rim of the one right before it.

With a bit of practice and an eye for detail, you can tell that the Rheita Valley is neither the youngest nor oldest feature in the lunar southeast. Notice a couple of battered craters on the valley’s northeastern flank. Their rims and floors appear worn down because they were pounded by later impacts, proving they formed earlier. Rheita Crater in the northeast and Young D at the south end clearly came later because they look sharper and obviously reshaped the underlying valley.

The Rheita Valley is the longest and widest valley on the nearside. But many similar crater chains surround large impact features. The chains form as debris from an impact shoots out in linear sprays like the spokes on a bicycle wheel. The Rheita Valley’s size implies that the impact must have been big. It was: It blasted out Mare Nectaris (Sea of Nectar) to the north.

Sunrise occurs over the Rheita Valley on January 8, but the image more closely matches what you’ll see on the 9th. Take another look on the 22nd and 23rd, when the Sun sets over this region. The reversed lighting helps you see that the valley points right back to its origin in Mare Nectaris.

Catch the year’s best meteor shower

Streaks of light should pepper the night sky when the Quadrantid meteor shower peaks the night of January 3/4. With New Moon arriving just 48 hours later, dark skies prevail all night. None of this year’s other major showers fares as well. As long as the weather cooperates, observers in rural areas should see a nice show.

Scientists expect the shower to peak around 9 p.m. EST. Sadly, the radiant — the point from which the meteors appear to originate — doesn’t climb high until early morning. And rates drop dramatically from the peak. The Quadrantids can produce up to 120 meteors per hour at maximum, but that number drops to 30 just eight hours on either side. Although North American observers should see a good display, the best views likely will come from Europe.

The radiant lies in northern Boötes, an area once claimed by the now-defunct constellation Quadrans Muralis. That’s where the shower gets its name.

The brightest comet of 2018 remains a nice sight in January as it treks eastward against the background stars of Lynx and Ursa Major.
Flying right under the Bear’s nose

Comet 46P/Wirtanen became the brightest periodic comet of 2018 in December, and it starts 2019 in nearly as good shape. Astronomers expect it to glow around 7th magnitude in early January as it crosses the border from northeastern Lynx into western Ursa Major. Fortunately, this region remains visible all night from mid-northern latitudes, climbing highest soon after midnight local time. Use 3rd-magnitude Omicron (ο) Ursae Majoris — the nose of the Great Bear — as your guide. Wirtanen slides 1° south of Omicron on January 10.

The comet made its closest approaches to both the Sun and Earth in December, and it is now leaving the inner solar system. Not surprisingly, this leads to a drop in brightness. Wirtanen may dip to 9th magnitude by month’s end, so try to observe it during the Moon-free block of time in January’s first 10 days.

A telescope should reveal the comet’s sharp eastern flank. This is where solar radiation ionizes the gas escaping from Wirtanen, and the solar wind picks up these ions and pushes them directly away from us. Through 10-inch and larger instruments, you might see a hint of green on this edge. In contrast, the dust leaving the comet curves gently into a fan-shaped tail.

When Wirtanen returns to the inner solar system in 2024, it will be farther from Earth and likely won’t make our viewing list. We’ll have to wait 27 years for the comet to come close to Earth again and light up our night sky.

Asteroid 433 Eros swoops by Earth in January, brightening to 9th magnitude as it makes one of its rare close approaches to our planet.
An asteroid on a deadly mission?

For an asteroid named for the Greek god of desire, 433 Eros doesn’t show Earth much love. Although the orbit of this near-Earth object doesn’t quite intersect our planet’s path, it comes close, and astronomers suspect that gravitational perturbations will turn it into an Earth-crosser one day. In fact, there’s a non-negligible chance that it will slam into our world a billion or more years from now. If it does, it won’t be pretty: It would pack more punch than the asteroid that helped wipe out the dinosaurs.

For observers, Eros makes one of its periodic close passes by Earth this month. At closest approach January 15, the asteroid comes within 19 million miles of our planet. But it remains nearly this close all month, glowing at 9th magnitude from its perch high in the east after darkness falls. A small telescope will let you follow Eros as it heads south along the Perseus-Auriga border before entering Taurus near month’s end. Avoid searching between January 15 and 19, when the waxing gibbous Moon spills too much light into this region.

The asteroid travels nearly 1° per day, so it takes only 30 minutes to shift position noticeably at 100x. The chart below will get you to the right field. Make a sketch of the stars in the vicinity, going deep enough to include Eros. Then, take a 30-minute break before returning to the field and noting which dot has moved the apparent width of Jupiter’s disk. If you watch for half the night, you also should notice the asteroid’s brightness vary by half a magnitude during its five-hour rotation.

Eros typically doesn’t glow as brightly as it does this month. It won’t beat 9th magnitude again until 2056, when it will peak at magnitude 7.6.



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