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Mercury and Venus peak

January 2011: Jupiter dominates the sky after sundown, and Venus gleams high before dawn. You can find Uranus through binos, and Mercury pops into view below Venus.
A waning crescent Moon passed below Venus (which appeared beneath Mercury) from Australia before dawn March 6, 2008. The same two planets team up early this month.
Mike Salway

The new year opens with great views of several bright planets. Two stand out: Jupiter dominates the sky after sundown, and Venus gleams high in the darkness before dawn. View more closely and you can find Uranus through binoculars as it lurks in Jupiter’s vicinity. And Mercury pops into view below Venus in early January; the two inner planets reach their greatest elongations from the Sun within a day of each other.

That leaves Saturn as the last of January’s bright planets. The ringed world rises shortly before midnight and rides high in the south as dawn breaks.

The other event of note this month is the Quadrantid meteor shower. This prolific shower peaks under a moonless sky the morning of January 4, offering a nice reward for those who brave the cold.

Let’s begin our tour of winter wonders where we typically do, in the western sky after sunset. You’ll want to catch Neptune during the month’s first 2 weeks when the 8th-magnitude planet lies low in the southwest after darkness falls. You can find it through binoculars about 2.5° west of the 4th-magnitude star Iota (ι) Aquarii. Or simply wait until January 7, when the eighth planet lies 5° south of the crescent Moon.

Neptune sets before 9 p.m. January 1 and an hour earlier by midmonth. If you don’t look within an hour after twilight ends, it will have dipped too low. A quick peek at ­Neptune through a telescope reveals a blue-gray disk that spans 2.2".

The crescent Moon attracts attention to Jupiter the evenings of January 9 and 10, though, truth be told, the ­brilliant planet doesn’t need much help. At magnitude –2.3, it’s the brightest point of light in the evening sky. Jupiter stands some 8° to the Moon’s left January 9 and an equivalent distance below it on the 10th. When the Moon is not near Jupiter, simply look for the steady beacon shining in the southwest.

Mercury and Venus share the morning sky in early January. The inner planets reach greatest elongation a day apart. Illustration by Astronomy: Roen Kelly

Jupiter shows more detail through a telescope than any other planet. And you’ll want to take advantage of the good views January offers because the gas giant will start sinking closer to the horizon — so its light has to pass through more of Earth’s turbulent atmos­phere — in February. This month, Jupiter remains at least 30° above the horizon as twilight fades.

Jupiter’s disk spans 37" across its equator in mid-­January, some 25 percent smaller than its apparent size at last September’s opposition. Observers will be keen to check for the return of the South Equatorial Belt, a normally dark band that all but disappeared less than a year ago. Some previous revivals dramatically changed the planet’s appearance within a few days.

Even a casual glance at Jupiter through a telescope reveals up to four bright moons. Io, Europa, Ganymede, and Callisto (in order of increasing distance from the planet) all orbit in Jupiter’s equatorial plane, which lies nearly along our line of sight.

The giant planet occasionally hides one or more of the three inner satellites. Once each orbit, a moon passes behind the planet and Jupiter both occults and eclipses it. Half a revolution later, the moon and its shadow transit the jovian disk. A transiting shadow appears conspicuous because the dark shadow contrasts nicely to the gas giant’s bright cloud tops. (Callisto orbits far enough from Jupiter that it currently passes above and below the disk, so it’s on view whenever the planet is.)

With Jupiter on display for only a few hours each ­evening, most satellite events happen when the planet is out of sight. Still, enough occur during the month that every observer has the chance to see several. Here is a sample of some of the better ones visible from North America.

Perhaps the best event occurs January 17, when the shadows of both Io and Ganymede transit Jupiter for 33 minutes. Io’s shadow appears as soon as night falls along the East Coast and leaves the disk at 8:15 p.m. EST. Ganymede’s shadow transit begins at 7:42 p.m. EST and ends at 10:26 p.m. EST. You can tell the two shadows apart because Ganymede’s appears larger.

Io and Ganymede team up again January 24, but this time Io’s shadow tracks across Jupiter’s face north of Ganymede. Io itself also transits until 9:05 p.m. EST, offering simultaneous views of two moons and one shadow on the cloud tops. Ganymede’s disk exits Jupiter at 10:07 p.m. EST, followed 3 minutes later by Io’s shadow.
Io’s and Ganymede’s shadows trek across Jupiter’s disk together the evening of January 17. Illustration by Astronomy: Roen Kelly

Jupiter currently occults the moons at its western limb. You can see Io disappear at 7:29 p.m. EST January 16. More than 3 hours later, at 10:55 p.m. EST (best timed for western North America), Io reappears from eclipse well off the planet’s eastern limb. From our current viewing angle, the gas giant’s long shadow extends far east of the disk, so these reappearances occur away from the limb. When Io re-emerges into sunlight, it joins the already visible Europa just 15" away.

Jupiter serves as a guide to Uranus. The two planets appear in the same binocular field all month. On January 2, Uranus lies 0.6° north of Jupiter. Both planets move slowly eastward relative to the background stars of Pisces, but Jupiter, which lies nearer to the Sun, moves faster. By the end of January, nearly 4° separate the two. A telescope reveals Uranus’ 3.4"-diameter disk, which sports a distinct blue-green color.

To the east of Jupiter and Uranus lie the bright stars of winter, which climb high in the south by late evening. Not long after midnight, the dimmer stars of spring become prominent in the east. Along with them comes a visitor from our solar system: glorious Saturn. The ringed planet stands high in the south by the time twilight begins.

Saturn resides among the background stars of Virgo the Maiden and remains within 2° of 4th-magnitude Theta (θ) Virginis all month. The planet shines at magnitude 0.7, slightly brighter than Virgo’s luminary, Spica, which rises nearly an hour after Saturn.

The new year begins with Saturn’s rings tilted 10° to our line of sight. This provides superb telescopic views, a welcome change after a few years when the rings appeared edge-on or with only a slight tilt. Look for the Cassini Division, a 2,900-mile-wide gap that separates the outermost A ring from the brighter B ring. The planet’s disk measures 18" across, and the rings span 40".

Saturn’s biggest moon, Titan, glows at 8th magnitude and shows up easily through small scopes. It passes due south of the planet January 12 and 28 and due north January 4 and 20. Several other moons show up through 6-inch telescopes. The easiest to see are the three 10th-magnitude moons: Tethys, Dione, and Rhea. Sometimes they pair up to better catch your attention. Rhea and Tethys lie near Saturn’s northwestern limb the morning of January 13, and Rhea and Dione appear near the planet’s southeastern limb two mornings later.
Uranus lies near Jupiter in early January, a great time to find the distant world with the guidance of the brilliant giant planet. Illustration by Astronomy: Roen Kelly

Iapetus is the oddest of Saturn’s bright moons. It wanders much farther from the planet, and its two-toned surface causes major brightness variations. Iapetus glows at its brightest, 10th magnitude, when it reaches greatest western elongation January 4. But it then lies a whopping 9' from Saturn — about 13 ring diameters. It appears brightest then because its highly reflective trailing hemisphere faces us. Iapetus swings 2' north of Saturn January 24, when it glows at 11th magnitude. It dims another full magnitude by the time its dark leading hemisphere faces us mid-February.

You can’t miss Venus as it climbs high in the morning sky this month. It rises more than 3 hours before the Sun and appears brilliant in the southeast well before twilight commences. Venus spends the first week of the new year in Libra the Scales. On January 7, it appears to pick up a moon. Alas, this is actually the 4th-magnitude star Theta Librae, which appears 2' south of the planet.

The next morning, Venus reaches greatest elongation when it lies 47° west of the Sun and shines at magnitude –4.6. The planet crosses from Libra into Scorpius January 9, but it stays only a few days among the Scorpion’s stars. Venus then moves into Ophiuchus January 14 and remains there for the rest of the month. On the 15th, it passes 8° north of 1st-magnitude Antares, Scorpius’ brightest star.

The period around greatest elongation is always a good time to view an inner planet through a telescope. On New Year’s morning, Venus shows a 27"-diameter disk that’s 46 percent lit. The planet’s diameter shrinks and its phase waxes throughout January. It appears half-lit at greatest elongation and shows a gibbous phase the rest of the month. On the 31st, it appears 20" across and 61 percent lit.

Mercury also puts on a good show before dawn, although it pales in comparison to Venus. It reaches greatest western elongation (23°) January 9, just a day after we witnessed Venus at the same configuration. Mercury shines at magnitude –0.3 that morning, brighter than any star then visible but much fainter than Venus.

Look for Mercury low in the southeast about an hour before the Sun rises. It climbs noticeably higher and remains conspicuous as twilight brightens during the next half-hour. Although its altitude peaks at greatest elongation, Mercury remains in view until January’s final days.

As with Venus, Mercury looks most interesting through a telescope around greatest elongation. The innermost planet spans 8" January 1 and shows a 38-percent-lit disk. On the 9th, look for a 7"-diameter disk that appears 64 percent illuminated. Late in the month, Mercury spans just 5" and displays a fat ­gibbous phase.
The Quadrantid meteor shower peaks January 4, when observers may see up to 120 meteors per hour from a dark site. Illustration by Astronomy: Roen Kelly

Hot flashes for a cold winter’s night

Observing prospects look excellent for this year’s Quadrantid meteor shower, which peaks before dawn January 4, the same morning as New Moon. The Quadrantids can produce up to 120 meteors per hour under perfect conditions. With the Moon out of the sky, this has the potential to be the finest shower of 2011.

The Quadrantids typically have a sharp peak, with the number of meteors dropping by about half 6 hours from the peak. Astronomers predict the maximum should occur around 1h UT January 4 (8 p.m. EST January 3). This timing works out best for those in Europe, but observers everywhere should keep an eye out.

The shower’s radiant lies in the northern part of Boötes the Herdsman. The Quadrantids got their name from a defunct constellation, Quadrans Muralis, which used to occupy this region.

The Altai scarp marks the western edge of Mare Nectaris, which a giant impact carved billions of years ago. Consolidated Lunar Atlas/UA/LPL

On the shores of a sweet sea

Viewing the lunar surface through a telescope is likely the closest any of us will get to experiencing the “magnificent desolation” Buzz Aldrin felt during his moonwalk. And few sights can compare to the chain of features that hug the day-night terminator on a 5-day-old Moon. On the evening of January 9, the crater Posidonius and the Serpentine Ridge dominate the Moon’s northern half while the bright-rimmed dark hole of Theophilus catches the eye near the equator.

You’ll find the dark plains of Mare Nectaris (Sea of Nectar) southeast of Theophilus. Long after a mighty blast carved out the Nectaris basin, lava bubbled up through cracks in the basin floor. This dark lava defines Mare Nectaris. But the basin extends much farther than what first greets the eye. Its western edge stands out nicely under grazing illumination January 9.

Nectaris’ true rim takes the form of Rupes Altai (the Altai scarp), a bright arc that continues southeastward until it reaches the more recent crater Piccolomini. As the Sun climbs higher over this region during the next few hours on the 9th, the northern part slowly comes into view. It appears more noticeable the following night.

When to view the planets
Jupiter (southwest) Saturn (east)
Mercury (southeast)
Uranus (southwest)
Venus (southeast)
Neptune (southwest)
Saturn (south)
Comet 103P/Hartley loops to the east of Sirius this month, like a leash trailing from the Dog Star. Illustration by Astronomy: Roen Kelly

A “hairy star” dogs Sirius

It’s a treat to be able to find a modestly bright comet quickly, and that’s the case this month because 103P/Hartley lies within a few degrees of the sky’s brightest star. You can follow Hartley’s nightly path relative to gleaming Sirius with an 8-inch telescope from the suburbs, or see it frolic in front of a star-filled background with a 4-incher under country skies. In midevening, the comet lies well up in the southeastern sky.

Now past its October peak, the ages-old ball of primordial ice and dust is cooling its jets with increasing distance from the Sun. The comet is pulling away from Earth, too, so it fades from 8th to 9th magnitude. Hartley revolves around the Sun on a path that takes it from just beyond Earth’s orbit out to Jupiter’s. When Earth passes it, the comet performs a retrograde loop in the sky, behaving like one of the outer planets. It’s just lucky timing that the loop occurs near Sirius.

Moonlight begins to interfere after January 10 but retreats for the month’s final week. For astroimagers and visual observers alike, Comet 103P/Hartley poses next to the compact star cluster M50 for a couple of nights as the calendar turns to February.

The asteroid Fides passes through the Pleiades star cluster (M45) early this month, offering a challenge to backyard observers. Illustration by Astronomy: Roen Kelly

Fides passes through the Pleiades

Even ancient observers recognized the Seven Sisters as a cluster of stars. This sparkling group, also known as the Pleiades and M45, plays host to the main-belt asteroid 37 Fides during January’s first half. It’s a snap to point your telescope to the right field because the Pleiades remains on display nearly all night.

Glowing at magnitude 10.4, this 67-mile-wide asteroid ranks among the faintest and smallest such objects we have featured in this column. What makes this otherwise-unremarkable space rock worth seeking is the magnificent backdrop provided by what is arguably the sky’s most beautiful star cluster.

Simply use the chart at right to guide you to the asteroid’s location and pick it out of the rich background. Then return to the same field 2 or 3 nights later; the “star” you picked has moved.

German astronomer and asteroid hunter Karl Luther discovered 37 Fides in 1855. He named it after the Roman goddess of loyalty. Luther was a successful hunter of solar system debris — Fides was the fifth of his 24 discoveries.

Martin Ratcliffe
provides professional planetarium development for Sky-Skan Inc. Alister Ling is a meteorologist for Environment Canada.


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