From the January 2006 issue

Saturn rules the night

January 2006: The ringed planet stands head and shoulders above its planetary brethren in January, despite Mars' valiant attempt to compete.
By and | Published: January 1, 2006

Meteors and moons

Winter’s stellar shower
One of the year’s best meteor showers — but ironically one of the least observed — makes its appearance in early January. The Quadrantid meteor shower remains active from January 1 to 5, peaking on the 3rd. Two factors conspire against the Quadrantids: They come at the coldest and cloudiest time of year, and the number of meteors drops off dramatically from a sharp peak, so observing more than a day away yields few sightings. The deep sky

A pair of binaries
In an April Fool’s newsletter of an Edmonton, Alberta, astronomy club, a member once joked that Camelopardalis was Latin for “large vacant area of sky.” With the naked eye from a suburban backyard, most would find this an apt description of the constellation. But don’t let this mislead you: Several treasures await in the apparent void.

Camelopardalis’ two brightest stars lie about halfway between Polaris and the bright star Capella in the northeast. The one closer to Capella is the double star Beta (β) Camelopardalis. Its 7.4-magnitude companion is a challenge for binoculars, but any scope will show it easily. The wide pair 11 and 12 Cam lies 1.5° closer to Capella. Approximately 3′, or 10 percent the Moon’s apparent width, separate these two, so they appear as distinct points of light through binoculars.

It surprises many beginners to learn binoculars open up a realm not accessible with a telescope. Their wider field of view reveals larger structures that remain all but invisible through a scope. To view the binocular treats in Camelopardalis, head to a dark location during the second half of the month, when the Moon is out of the sky. On the prime meridian
Bisect the Moon’s visible hemisphere from north to south pole, and the line would scrape the eastern edge of a trio of prominent craters. Ptolemaeus lies farthest north, just south of the lunar equator. Next comes Alphonsus, and then this month’s highlight, Arzachel. The three show up nicely even in small telescopes.

Arzachel is the smallest and geologically youngest of this spectacular trio. The 60-mile-wide crater’s heavily terraced walls reach higher than those of its two larger neighbors. Two smaller impact craters and an off-center mountain peak dominate the rough crater floor. A distinctive rille cuts across the floor’s eastern half and shows up nicely under good conditions. When the Sun sets over Arzachel, the rille projects a long shadow toward the eastern wall. The best views come as the Sun rises over the crater near First Quarter phase (January 6) and as the Sun sets around Last Quarter phase (January 22). Mark your calendar for the first evening of the new year, when a crescent Moon joins Venus. Through a telescope, Venus also shows a delightful crescent shape, while steadily held binoculars reveal a tiny, delicate arc. Sharp-eyed observers just might see an elongated streak without optical aid.

The cusps of Venus’ crescent elongate and join on the other side at inferior conjunction, when the planet lies between the Sun and Earth. You can view this phenomenon only when Venus passes far enough from the Sun so you won’t blind yourself looking. On January 13 at local noon, the planet stands 5.5° (about one binocular field) above the Sun and has only 0.5 percent of its disk illuminated. Make sure to hide the Sun behind the roof of a house or garage, put your scope in its shadow, and sweep straight up.

Observers in North America have ringside seats the evening of January 9 as the Moon passes in front of the bright Pleiades star cluster (M45). It’s exciting to watch one star after another disappear instantly as the Moon’s dark limb snuffs them out. Lucky observers from Texas to New England will have the chance to see a grazing occultation of Merope. This 4th-magnitude star pops in and out of view as peaks and valleys along the Moon’s limb graze past. Another 4th-magnitude Pleiad, Atlas, does the same thing for viewers from Southern California to Michigan’s upper peninsula. To find times for these events at your observing location, check out the International Occultation Timing Association’s web site.

On January 4, Earth makes its closest approach to the Sun for the year. The perihelion of our slightly elliptical orbit brings us 1.5 million miles closer than average. As soon as the January sky darkens, Saturn pokes above the eastern horizon. Resist the temptation to look too early, however. The planet’s low altitude severely affects the view’s clarity. By 10 p.m. local time January 1, Saturn has climbed 30° in the east. Few experiences match frozen fingers trying to focus a telescope, only to be rewarded with a spectacular, crisp view of Saturn’s rings.

By the end of January, Saturn reaches this respectable altitude 2 hours earlier, and by 10 p.m., your frozen fingers will be ready for a hot cup of cocoa.

Saturn reaches opposition January 27, the peak of its current apparition. It then lies closest to Earth, 755 million miles away. You can spot it easily among the faint stars of Cancer the Crab. Throughout the month, Saturn lies in the same binocular field as the prominent Beehive star cluster (M44). This spectacular chance alignment gives observers an added treat.

Saturn shines at magnitude –0.2 during most of January, and the planet’s disk swells to 20″ at opposition. Its rings, however, more than double this apparent size, spanning 46″. We now find ourselves within 3 years of an edge-on view of the rings. A few years ago, the entire outer ring could be traced south of the planet’s disk thanks to the greater tilt. Now, the disk blocks the ring. Still, a small scope delivers great views of the rings and of the Cassini Division, a dark gap that separates the outer A ring from the brighter B ring. Kemble’s Cascade
To find our first stellar group, aim at a point halfway between Polaris and Capella, then shift about one binocular field (6°) toward Alpha (α) Persei. You should see a striking chain of 7th- to 9th-magnitude stars spanning half the field, with a couple of pairs thrown in. This pretty arrangement is called Kemble’s Cascade. Astronomers designate such groups asterisms, when the stars catch the eye but whose members are physically unrelated.

In contrast, stars born together have similar ages and move with one another through space. If gravity only loosely binds the stars, astronomers call these groups associations. A nice example, the Camelopardalis OB1 association, lies one binocular field southwest of Kemble’s Cascade. The O and B stand for the spectral letters of hot stars. A more distinct OB association, the Alpha Persei moving group, lies nearby.

Gravity’s hold on associations is so weak they disperse after a revolution or two around the Milky Way’s center. Groups with greater numbers of stars exert more gravity and can stay together much longer. Such open clusters abound in and near the galaxy’s spiral arms. A classic example in Camelopardalis is NGC 1502, which lies at the southern end of Kemble’s Cascade. In fact, Saskatchewan amateur Father Lucian Kemble was looking for NGC 1502 when he stumbled across the star chain some 30 years ago.

Through a telescope, NGC 1502 displays a pair of yellow suns set against a triangular splash of stars. At magnifications of 150x or more, you should spot some tight pairs. Vesta with only the eyes
This month, you have a rare chance to see the brightest asteroid without optical aid. Vesta reaches opposition in Gemini January 5, when it glows at magnitude 6.2 — an easy target for binoculars from the suburbs and barely within range of the naked eye at a pitch-black observing site. To find it, point your binoculars about one-third of the way from Delta (δ) to Epsilon (ε) Geminorum. The second-brightest dot you’ll see is Vesta. Jupiter rises about 3 a.m. in early January and lies 30° high in the southeast as dawn breaks. It dazzles us in the normally faint region of sky occupied by Libra the Scales.

On January 23, Jupiter lies 5° above the waning crescent Moon. If you’re an early riser, Jupiter makes a great target for your telescope. You’ll have no problem spying its four bright moons and two dark equatorial belts — the first atmospheric features most people ever see on another planet. Experienced observers know that spending a few extra minutes at the eyepiece will bring more subtle atmospheric features into view.

Innermost Mercury remains visible in the morning twilight as January opens, but it’s sinking fast. It lies 15° west of the Sun January 1 and rises an hour before our star. But the shallow angle of the ecliptic to the southeastern horizon before dawn this time of year hinders the view. You’ll need a flat horizon and good atmospheric transparency to spot it.

As Mercury disappears behind the Sun this month, Venus passes in front of our star. Venus’ rapid motion means it appears low in evening twilight during January’s first week and low in morning twilight during the month’s final 10 days. The planet’s brilliance helps it shine through the twilight glow.

The best views for Northern Hemisphere observers come toward the end of January. On the 27th, a slim crescent Moon stands 15° to Venus’ lower right. A telescope shows Venus has the same 7-percent illumination as the Moon. The planet then measures a hefty 57″ across.

Finally, Earth makes its closest approach to the Sun for the year this month. On January 4, our home planet reaches perihelion, when it lies 91.4 million miles from the Sun. Comets and asteroids

Cruising the water signs
Comet C/2005 E2 (McNaught) remains on a Mars-like orbit this month, like it has for the past several months, plying the ecliptic and edging eastward at a speed that keeps it comfortably ahead of the Sun. This geometry means our viewing angle actually improves in January. As the sky grows dark, Comet C/2005 E2 appears slightly higher in the sky than it did toward the end of 2005. With a diameter of about 320 miles, Vesta is the third-largest asteroid in the main asteroid belt. It has one of the most reflective surfaces of the bunch. An average piece of the Moon’s surface actually reflects much less light — it appears white only because it is so bright overall.

One 5th-magnitude star lies between Delta and Epsilon Gem, along with a handful of 6th-magnitude stars. To be sure you’ve found Vesta, make a quick sketch of the positions of 4 or 5 stars and check back a day or two later to identify the interloper. Then, if you’re under a dark sky, see if you can spy Vesta with your naked eyes.

Vesta is the only asteroid on good display this month. The next best, 3 Juno, glows 2 magnitudes fainter. You can find it in the shield of Orion, where it is nicely placed in the evening sky. The slowly moving asteroid passes within a degree of 4th-magnitude Pi55) Orionis between January 20 and 26.

Martin Ratcliffe is former president of the International Planetarium Society. Alister Ling is a meteorologist for Environment Canada. Although Mars will remain in the evening sky for many months, its diminishing size will reduce its appeal as a telescopic target after this month. On January 1, the planet has a respectable 12″ apparent diameter and shines at magnitude –0.6. Telescopes with apertures of 6 inches or more will capture plenty of surface features. For example, in the early evening (8 p.m. EST) of January 1, Mars’ gibbous disk displays Meridiani Sinus prominently. At the same time January 10, Syrtis Major — the planet’s most conspicuous dark feature — lies at the center of the martian disk.

Mars’ diameter falls below 10″ by January 19. An early evening view shows Mare Sirenum dominating the southern hemisphere. Later in the evening, Mare Cimmerium and Mare Tyrrhenum appear prominently.

By the end of January, Mars has dimmed noticeably to magnitude 0.2 and shows a more distinct gibbous phase. The “eye” of Mars, Solis Lacus, then appears front and center on the planet’s 9″-diameter disk in the early evening. Observers lucky enough to have steady atmospheric conditions and a 10-inch or larger scope will get good views. Any telescope shows Saturn’s brightest moon, 8th-magnitude Titan. It lies due north of the planet January 1 and 17 and due south January 9 and 25.

On the 25th, take care not to confuse Titan with a brighter star that lies in the same field
of view. Gazing at Titan this year may feel a little different.

It was just 12 months ago that Europe’s Huygens probe landed on the moon’s surface, giving professional and amateur astronomers alike their first close-up look at the surface of this haze-shrouded world.

Saturn’s other moons prove more challenging to observe.

A 6-inch scope will bring the 10th-magnitude trio of Tethys, Dione, and Rhea into view. Tethys zips around the planet in less than 2 days, Dione takes nearly 3 days, and Rhea more than 4 days.

Iapetus is just as easy to see when it lies far west of Saturn and glows at magnitude 10.1. But it appears 5 times fainter at greatest eastern elongation because its coal-black hemisphere then faces us directly. Iapetus spends January moving from west to east of the planet and fading steadily. On January 10, the two-faced moon passes a little south of the planet’s disk. The planets

As the winter Sun sets in the southwest, Mars glimmers high in the southeast. You’ll find it as a bright, ruddy object west of the Pleiades, or Seven Sisters, star cluster (M45). During January, Mars moves eastward relative to the background stars through the constellation Aries, ending the month just 8° shy of the Pleiades. On January 8, a waxing gibbous Moon stands beside Mars, drawing attention to the Red Planet. The modestly faint comet — predicted to glow around 10th magnitude — still has to contend with light pollution, both from the Moon and any city.

To get a decent view, wait until after January 16 to get the Moon out of the way, and head out to the country. Comet McNaught glides across the star fields of Aquarius the Water-bearer for most of January before entering Pisces the Fish toward month’s end.

While you’re in the area, take a peek at Uranus. The planet lies about halfway between 4th-magnitude Lambda (λ) Aquarii and 5th-magnitude Sigma (σ) Aqr. The planet’s tiny disk (3.4″ across this month) won’t reveal any features, but its conspicuous blue-green color is always an eye-catching treat.

No bright galaxies lie near McNaught’s path, so the first faint fuzzy you see will be the comet. Bump up the magnification a bit and take a longer look. The slightly darker sky provided by higher powers will boost the contrast. On January 20, the comet passes 15′ south of NGC 7351, an obscure 12th-magnitude galaxy. For images of comet encounters with other deep-sky objects, check out Viewing conditions should be good this year, with the waxing crescent Moon setting before 9 p.m. local time. Earth crosses the thickest part of the shower’s stream around noon EST on the 3rd, so observers should try viewing early that morning (the night of January 2/3). As always, find a spot far from artificial lights if you want the best view.

The shower’s radiant lies in Boötes the Herdsman. This region used to belong to the now-defunct constellation Quadrans Muralis, the shower’s eponym. The radiant passes nearly overhead as dawn approaches, so lucky observers might see rates approach 100 meteors per hour.

Quadrantid meteors hit Earth’s atmosphere at 25 miles per second. The incinerated dust particles apparently derive from debris ejected by the near-Earth asteroid 2003 EH1. The lord of the rings reaches the peak of its annual cycle this month. Saturn, ruler of the planets in mythology, dominates the sky from dusk to dawn. It lies opposite the Sun in our sky January 27, a configuration astronomers call an opposition. The planet then rises at sunset, climbs highest around midnight, and sets near sunrise. It also shines brightest and appears largest through a telescope.

You might be tempted to observe Saturn as soon as the sky grows dark, but the view improves as the planet ascends during the evening. Turbulence in Earth’s atmosphere causes blurry images, and the lower in the sky an object lies, the more atmosphere you have to peer through. For the same reason, avoid looking over rooftops or paved parking lots, where escaping heat can ruin the view.

A week or two before and after Saturn reaches opposition, its shadow disappears. It’s the same phenomenon you see on a clear day if you stand directly between a friend and the Sun. Your friend’s shadow vanishes because it lies behind him or her. But shift your head a bit to one side or the other, and the shadow pops into view. It’s well worth following Saturn’s changing shadow each clear night in the weeks around opposition. During the same time, you’ll see the planet’s brightest moons also shifting positions around the ringed wonder.

The steady orange beacon high in the south in the early evening is our closer planetary neighbor, Mars. It shines as brightly as Saturn, but only because its smaller disk lies much closer to Earth. Mars hangs around the evening sky until summer, so you might think you have plenty of time left to observe its subtle features. Alas, the orbits of Earth and Mars conspire to shrink the martian disk to a challenging size by February. It won’t be as big and bright as it is now until October 2007.

From its perch in the evening twilight, Venus dives toward the Sun. For the past several months, the planet seemed frozen in twilight’s golden glow. But Venus takes only 2 weeks to disappear.