One of the great pleasures in observing the night sky is viewing the planets through a telescope. At almost any time of the year, either Jupiter or Saturn (or both) will be on display. Add to those the occasional appearances of Mercury and Venus, and there's always something new to see.
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Mars ranks as more of a rarity. Once every 26 months or so, the Red Planet makes a grand appearance. That time is now. Mars reaches opposition and peak visibility in January, when it rightfully claims the bulk of our planet-viewing attention.
Mars does have some competition, however. Brilliant Jupiter makes its final stand in the evening sky before twilight swallows it. Shortly before midnight, Saturn joins the scene. And with Saturn high in the south before dawn in late January, Mercury puts on a nice show.
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Let's start our tour of the solar system where we normally do, in the western sky shortly after sunset. The first object you'll see is Jupiter. The giant planet shines at magnitude -2.1 in the southwest and appears as a beacon against the background stars. It crosses from Capricornus into Aquarius during January's first week.
As the year begins, Jupiter sets nearly 4 hours after the Sun and remains conspicuous even after twilight fades away. But by January's close, the observing window shrinks noticeably. Jupiter then sets during late twilight, less than 2 hours after sunset.
This low altitude means viewing the planet through a telescope will highlight Earth's turbulent atmosphere more than fine features in Jupiter's atmosphere. Unless you have exceptional conditions, don't expect to see more than two dark belts on the planet's 34"-diameter disk.
Although atmospheric features will be difficult to discern, Jupiter's four bright moons will continue to stand out. Look for Io, Europa, Ganymede, and Callisto as they dance around the planet. If you're lucky, one of the moons will cast a shadow on the jovian cloud tops.
There's another good reason to view the moons this month. January marks the 400th anniversary of when Galileo discovered these four satellites. The great Italian scientist spotted Io, Europa, and Callisto January 7, 1610, and Ganymede 6 days later. Even the smallest modern telescope outperforms Galileo's instrument, so the moons show up as bright pinpoints of light arrayed on either side of Jupiter.
Distant Neptune lies just 2[degrees] to Jupiter's lower right as January begins. Look for it through a telescope during 2010's first week when it still appears against a dark background. The 8th-magnitude planet disappears into the twilight glow around midmonth. Count yourself lucky if you simply spot Neptune's blue-gray dot.
Uranus fares better. It lies one constellation east of Jupiter, sliding from Aquarius into Pisces in mid-January. Uranus appears to Jupiter's upper left and sets some 2 hours after the brighter planet.
Uranus glows at magnitude 5.9 and shows up easily through 7x50 binoculars. You'll need a small telescope to see the planet's blue-green disk, which spans 3.4". Look for Uranus below Pisces' Circlet asterism, some 5[degrees] south of the 5th-magnitude star Lambda (e) Piscium.
By late January, Mars shines conspicuously in the east as darkness falls. It passes from Leo the Lion into Cancer the Crab during January's second week, although you don't need any background stars to identify the planet. Mars appears distinctly reddish and shines brighter than any other point of light in the sky except for Sirius (which lies well to Mars' right) and Jupiter (which sets in the west not long after Mars appears). Mars brightens by more than 50 percent this month, climbing from magnitude -0.8 January 1 to magnitude -1.3 at opposition January 29.
Although Mars appears biggest through a telescope around opposition, it remains quite small. Its apparent size grows from 12.7" January 1 to its peak of 14.1". Although a nearly Full Moon passes Mars both January 2 and 29, you don't need a dark sky to observe the planet.
For the best views of the martian disk, wait until the planet climbs high in the south around midnight. Its greater altitude then means you'll view it through less of Earth's turbulent, image-distorting atmosphere.
Mars rotates on its axis once every 24 hours and 37 minutes. This extra half-hour above and beyond Earth's rotation means that if you view Mars at the same time each night, the surface will appear to rotate backward 9[degrees] from one night to the next. This shift accumulates during the course of a month to let you view most of the martian surface. Of course, the planet rotates almost 15[degrees] each hour, so observing all night presents most of the surface to you as well. Just remember to bundle up against the cold.
Mars' white north polar cap continues to dominate the disk because the planet's north pole now tilts toward Earth. Features closer to the equator appear best when they lie near the disk's center. The following list summarizes when some prominent features lie near Mars' central meridian at midnight EST (9 p.m. PST): on January 1, Sabaeus Sinus, Mare Acidalium, and Chryse Planitia; January 7, Sabaeus Sinus, Syrtis Major, and Hellas; January 14, Syrtis Major and Hellas; January 21, Mare Cimmerium, Mare Sirenum, Elysium, and Amazonis; January 28, Solis Lacus, Tharsis, and Olympus Mons (which is visible only in large backyard telescopes).
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By the time Mars reaches its highest position in the south, Saturn already shines brightly in the southeast. Saturn now lies among the stars of Virgo the Maiden. At magnitude 0.8, it shines slightly brighter than that constellation's brightest star, Spica. Saturn will brighten a bit more by the time it reaches opposition in March.
The ringed planet parks 1[degrees] north of the 4th-magnitude star Eta (c) Virginis all month. Saturn barely moves relative to Eta because the planet's eastward motion comes to a halt in mid-January. Saturn then starts to move westward, but picks up speed slowly.
Saturn's disk spans 18" in mid-January, and the rings extend more than twice this width. The rings tilt 5[degrees] to our line of sight, their widest since 2008. They will narrow somewhat by summer, but widen even more by the end of 2010.
Any telescope will show you 8th-magnitude Titan, Saturn's brightest moon. It lies close to the planet's disk the mornings of January 2, 10, 18, and 26.
Several fainter moons provide more of a challenge. Tethys, Dione, and Rhea glow at 10th magnitude and show up easily in 6-inch telescopes. All three orbit closer to Saturn than Titan does. Iapetus, on the other hand, lies much farther from the planet and takes 80 days to complete an orbit.
But that's not what makes Iapetus special. This moon has one hemisphere as dark as coal and the other as bright as freshly fallen snow. As the moon orbits Saturn, it changes brightness dramatically. It appears brightest when farthest west of Saturn and dimmest when farthest east.
Iapetus reaches greatest eastern elongation January 10, when it glows at 12th magnitude and will be difficult to spot through an 8-inch scope. As January progresses, Iapetus heads westward. It passes 1.5' due south of Saturn the morning of January 29--a good time to spot this 892-mile-wide moon.
As twilight starts to paint the sky in the second half of January, try to spot Mercury. The innermost planet passes between the Sun and Earth (a configuration known as inferior conjunction) January 4 and then leaps into the morning sky. You may spot it as early as January 13, when it appears 7[degrees] high in the southeast 30 minutes before sunrise. If you have exceptionally clear skies and a flat horizon, look for a thin crescent Moon 5[degrees] south of Mercury.
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Mercury shines at magnitude 0.8 that morning, but it brightens rapidly. It climbs to magnitude -0.2 by January 26/27, when it reaches greatest elongation. The planet then lies 25[degrees] west of the Sun and appears 9[degrees] above the horizon 30 minutes before sunrise.
A telescope reveals rapid changes in Mercury's appearance. On January 13, the planet's disk spans 9" and appears 23 percent lit. Its phase waxes to half-lit January 21 and to 63 percent illumination by the 27th. On that morning, Mercury measures 7" across.
The sky's brightest planet remains out of sight all month. Venus reaches superior conjunction January 11, when it lies on the far side of the Sun from Earth.
At 7 p.m. EST January 2, Earth reaches perihelion the closest point to the Sun during its yearly orbit. At perihelion, Earth lies 91.4 million miles from the Sun, some 3.1 million miles closer than at its farthest point in early July.
Earth's proximity to the Sun this month causes our star to appear slightly larger in the sky. This contributes to one of January's more impressive events: an annular solar eclipse. On the 15th, the Moon passes directly between the Sun and Earth. But the relatively small Moon on that date fails to cover the big Sun, leaving a ring of sunlight visible at maximum.
Observers will see this annular eclipse along a narrow path that begins in central Africa and then treks across the Indian Ocean, through southern India, Sri Lanka, Burma, and, ultimately, China. Viewers in much of Africa, eastern Europe, and Asia will witness a partial eclipse. Be sure to use a safe solar filter to directly view the eclipsed Sun.
On the morning of January 1, skywatchers in Asia and Australia will see a partial lunar eclipse. At maximum, 8 percent of the Moon lies in Earth's umbral shadow. From Africa, Europe, and the northeastern and northwestern corners of North America, this eclipse occurs on the evening of December 31.
40 Red Planet delight A B C
49 Meteor watch A
49 Rising Moon C
50 When to view the planets A B C
50 Galilean moons on parade C
50 Comet search C
51 Locating asteroids B C
51 The Moon eclipses the Sun A B C
A = Visible to the naked eye
B = Visible with binoculars
C = Visible with a telescope
When to view the planets
EVENING SKY MIDNIGHT MORNING SKY
Jupiter (southwest) Mars (southeast) Mercury (southeast)
Uranus (southwest) Saturn (east) Mars (west)
Saturn (southwest)
Martin Ratcliffe and Alister Ling describe the solar system's changing landscape as it appears in Earth's sky.
Martin Ratcliffe provides professional planetarium development for Sky-Skan Inc. in Nashua, New Hampshire. Meteorologist Alister Ling works for Environment Canada in Edmonton, Alberta.
Source Citation
Ratcliffe, Martin, and Alister Ling. "January 2010: Mars shines big and bright." Astronomy Jan. 2010: 40. Academic OneFile. Web. 3 Jan. 2010.
Gale Document Number:A213691634
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