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Articles by J. Alex Knoll

A gas giant, that isIt’s a Gas

Jupiter is brilliant from dusk to dawn, rising in the east at twilight, at its highest due south around midnight and low in the west at dawn. The gaseous giant is at its closest, and Tuesday marks its opposition, when it is directly opposite the sun in relation to earth. The planet is at its best for viewing, and even a modest telescope will reveal its colored bands and its four largest moons.
    Mars rises around midnight and is well placed in the south as daybreak approaches. Over the next three months the red planet grows in size and brightness as it moves closer to earth.
    Saturn rises around 1:30am, trailing Mars by 20 degrees. Come dawn it’s high in the south-southeast. The bright star to its lower right is Antares.
    Venus twinkles just above the east-southeast horizon a half-hour before sunrise, while Mercury is a few degrees lower still, and almost lost now against the coming sun.

11 minutes a year can really add up

The moon wanes through late-night and early-morning skies this week, reaching last quarter Tuesday. The moon rises Thursday around 9pm, with the bright star Spica trailing about 10 degrees behind. Far to the west of the moon is Jupiter, the next-brightest object. Friday night Spica rises ahead of the moon, but now the two are less than five degrees apart.
    The moon rises just before midnight Sunday followed only minutes later by the red planet Mars, roughly five degrees to the southeast. As sunrise approaches Monday you’ll find them high in the south.
    The moon rises around 1am Tuesday, and now it’s six degrees to the left of Mars. Another red light, Antares, the heart of Scorpius, shines to the moon’s lower left, and it, the moon and Mars form a tight triangle. Ten degrees east of the moon is golden Saturn. The moon and Saturn are spectacular Wednesday before dawn, with the moon just two degrees above ­Saturn.
    Venus still glimmers low above the southeast horizon in the half-hour before daybreak. You may even spot Mercury lower still, though you may need binoculars.
    Monday marks Leap Day, that time every four years when we recalibrate our calendars to celestial time. You see, it takes the earth a little more than 365 days to orbit the sun, so we add a 366th day on each Leap Year to keep things in synch. You might think that Leap Year is a modern development. In fact, it was first enacted by Julius Caesar more than 2,000 years ago.
    Those early astronomers were able to track the earth’s annual passage around the sun to within 11 minutes — pretty good considering the telescope would not come along for another 1,400 years. While 11 minutes may seem insignificant over a typical year’s 525,600 minutes, it adds up to a full day every 130 years. By the 1500s, the vernal equinox fell on March 11 rather than the 21st.
    Enter Pope Gregory XIII, who in 1582 wiped from that year the days of October 4th through 15th. Further, he ordained that Leap Years would continue in years divisible by four except those ending in 00 — unless those 00 years were themselves divisible by 400. So back in 2000 we observed Leap Year, but in the year 2100 we will not. This reduces the difference between a solar year and our calendar year to 26 seconds, one day every 3,000 years!
    Again, pretty accurate computations at a time when the abacus was the most advanced mathematical instrument.

Look for them together from dusk Tuesday to dawn Wednesday

Sunset Thursday and Friday finds the waxing moon high overhead in the company of Gemini’s Castor and Pollux above, Canis Minor’s Procyon below and Orion’s Betelgeuse off to the west. Come Saturday the moon is in the constellation Cancer, too faint to compete against lunar glare.
    Come Sunday, the moon has a new companion, the bright star Regulus trailing a dozen degrees behind. The brightest star in Leo, Regulus is also part of the asterism called the Sickle of Leo, which looks like a backward question mark, the star marking the dot at the bottom.
    Monday’s full moon — the Snow Moon and the Hunger Moon — trails Regulus, while bright Jupiter follows the moon by roughly the same distance. Finally, Tuesday evening the moon and Jupiter are within two degrees of each another, appearing as a tight pair until sunrise.
    Just two weeks shy of opposition, Jupiter is at its best and brightest, rising in the east around 7:30pm and shining high in the south at 1:30am and brilliant above the western horizon at dawn.
    Dawn highlights the other four naked-eye planets. Mars rises around 1:30am, and by 6am it is high in the south. The red planet is just beyond the head of Scorpius, and it is 15 degrees from the scorpion’s red heart, the bright star Antares, whose name means Rival of Mars. You’ll have ample time to compare them in coming weeks as Mars drifts closer to Antares.
    Contrast that to golden Saturn to the east, creating a skewed triangle with Antares and Mars. You’ll find the ringed planet in the southeastern sky as dawn begins to brighten the horizon.
    Venus and Mercury rise just before dawn. Venus blazes brighter than all but the sun and moon, and Mercury, just a few degrees lower, shines at a respectable magnitude –0.1); even so, you’ll need an unobstructed view of the east-southeast horizon and likely binoculars to spot them.

Winters’ luminaries are giving way to those of spring

As dusk gives way to darkness around 6:30, the sky comes alive with the constellations of winter and some of the brightest stars in the sky. High in the south stands Orion, facing west toward the bull Taurus. Behind the hunter come his hounds, Canis Major and Minor. Above Orion are the stick-like figures of the Gemini twins, and to their east is a loop of stars forming Auriga the charioteer. The luminaries of these constellations themselves loosely form the Great Winter Circle, in which the waxing gibbous moon sits right in the middle Wednesday the 17th.
    While the winter constellations dominate the evening sky, those of spring are gathering to the east. At midnight, Leo the lion shines almost directly overhead, with Virgo and Boötes high in the east. As dawn draws near, Scorpius sprawls above the southern horizon.
    The pre-dawn skies are also host to all the naked-eye planets.
    Highest of the planets is Jupiter, rising around 9pm and midway between the bright star Regulus of Leo and Spica of Virgo. This is the best time of year for watching Jupiter. Even a modest telescope will reveal the gaseous giant’s equatorial bands and Great Red Spot as well as the planet’s four largest moons.
    The next planet in line, Mars, doesn’t rise until 1am, as far to the east of Spica as Jupiter is to the west. Over the next few months, the planet rises earlier and grows brighter nearing its closest approach to earth in late May.
    Saturn rises around 3am and is over the south-southeast horizon near dawn. Antares, the heart of the scorpion, is less than 10 degrees to the lower right. While the planet doesn’t climb especially high, its rings are tilted at a good angle for telescope viewing.
    The coming sun begins to bleach the eastern sky by the time Venus crests the horizon, but she shines so bright she easily cuts through the glare. But you may have to scour the skyline to find Mercury, which is less than four degrees below the Morning Star at dawn Saturday.

Five planets shine at dawn

Sirius the Dog Star, blazes high in the south by 10pm. The brightest star, Sirius is easy to spot, but if you have any trouble, follow the three belt stars of familiar Orion down and to the left.
    Last week we traveled the Great Winter Circle, which encompasses Sirius. The Dog Star also anchors another asterism, the Winter Triangle. The other two points are Betelgeuse, marking Orion’s upper shoulder, and Procyon, the Little Dog in Canis Minor, which together with Sirius, the lowest of the three, form a near-perfect equilateral triangle.
    For the first time since 2005, all five naked-eye planets are visible, aligned on the arc of the ecliptic before dawn. This week they are joined by the moon, as well.
    Jupiter leads the way. Old Jove in fact rises due east a little after 9pm and as dawn approaches is high in the west-southwest. Friday you’ll find the moon midway between Jupiter and Spica, the first-magnitude star of Virgo. Then Saturday the moon is less than two degrees to the upper left of Spica.
    To the east of Spica is Mars, which rises around 1am. Sunday before dawn the last-quarter moon is midway between Spica and Mars. Early Monday morning, the moon is just a few degrees to the upper left of Mars. Keep an eye on the red planet, as it draws closer to earth — and brighter — over the coming months.
    Saturn is next in line, rising in the east-southeast after 3:30am. Before dawn Tuesday the moon is between Saturn to the east and Mars to the west. Wednesday the ringed planet is just a few degrees beneath the waning crescent moon.
    Venus rises in the southeast around 5:30am, and once it’s crested the horizon there should be no mistaking this morning star, which is brighter than all but the sun and moon.
    The last planet, Mercury, is another matter, rising in the southeast amid the gathering glow of dawn. While brighter than most stars, the innermost planet is so tight against the horizon that you’ll have an easier time spotting it with binoculars. This week Mercury is within 10 degrees of Venus but will close the gap in the coming week, climbing higher and growing brighter before daybreak.

The Great Winter Circle beckons

The cold crisp air that might otherwise keep you inside provides some of the clearest and darkest skies of the year, so even with this week’s bright moon, some major stars and constellations stand out against its glare.
    Sunset Thursday finds the near-full moon high in the east, between Betelgeuse, the shoulder of Orion, below, and the twins of Gemini, Pollux and Castor, above. From these two stars wends the stars the Great Winter Circle, more aptly called the Great Winter Hexagon, which contains seven of the 23 brightest stars.
    To trace this asterism, begin with blueish-white Pollux (17), then look to honey-orange Castor (23) higher in the north. From there shoot to the northeast to golden Capella (6) of the constellation Auriga the charioteer. Next, drop southwest to red Aldebaran (14), the eye of Taurus the bull. Now shift your gaze to Orion’s foot, blue-white Rigel (7). Farther south is the hunter’s great dog, Canis Major, marked by Sirius, the brightest star in the heavens. Back to the northeast you’ll find the Little Dog Canis Minor and its lead star Procyon (8). Return to Pollux and you’ve closed the loop. While not part of the circle, Betelgeuse sits right in the middle and is the 10th brightest star.
    As the sun sets Saturday, January’s full Wolf Moon climbs into the eastern sky, trailing Castor and Pollux and to the left of Procyon. By Monday the now-waning gibbous moon has left behind the Great Circle and is just a few degrees to the south of another stellar luminary, Regulus (21), the heart of Leo the lion. Tuesday the moon is midway between Regulus to the west and Jupiter to the east. Wednesday night through dawn next Thursday, the moon is 10 degrees below Jupiter.
    Brighter than any star, Jupiter rises due east just after 9pm and is at its highest in the south at 3am. By that time Mars, rising around 1:30am, will be well above the southeast horizon. Saturn rises just after 4am, followed 90 minutes later by Venus, brighter than all but the sun and moon. Saturn and Venus are about 15 degrees apart, but the Morning Star sinks lower day by day while Saturn inches higher. As the coming sun starts to glow in the east, see if you can spot Mercury low against the horizon; binoculars may help spot this last of the naked-eye planets.

Watch the moon occult Aldebaran

As the sun sets, the hourglass shape of the great hunter Orion is already well positioned in the southeast. His foot, blue-white Rigel, is to the lower right, while his shoulder, red-orange Betelgeuse, is at the opposite corner to the upper left. The three stars of Orion’s belt point almost straight up from the horizon, and following them up and to the right leads you to Taurus the bull.
    Most prominent in Taurus is its fiery eye, the orange-red star Aldebaran. From there look for the bull’s face, marked by the V-shaped Hyades star cluster. Aldebaran is at one leg of the V, although not itself a part of the Hyades. Higher to the right marking the bull’s shoulder is the Pleiades Cluster.
    Monday the waxing gibbous moon sits at one point of a triangle with Aldebaran and the Pleiades, although you may be hard-pressed to spot the cluster against the glare of the moon.
    Tuesday after sunset look for the moon just right of Aldebaran and the Hyades Cluster. Then, just before 9:30, watch as the moon passes over the bull’s fiery eye, occulting it from view for almost an hour.
    In the hour before sunrise, clear skies in the southeast should allow you to see the four naked-eye planets currently visible. Closest to the horizon are Venus and Saturn. There should be no mistaking Venus, blazing at –4 magnitude. Saturn, roughly 10 degrees higher, is more than 60 times dimmer at magnitude +0.5. Don’t confuse Saturn with the nearby star Antares; the ringed planet shines with a steady yellowish glow, while the not-quite-so-bright star twinkles with a red hue. Antares, Saturn and Venus do, however, form a nice triangle.
    Imagine a line from Venus to Saturn, and extend it another 20 degrees or so to find Mars and farther still for Jupiter. Mars is not as bright as Saturn, while Jupiter is the next-brightest starlike object after Venus. You should be able to tell both from blue-white Spica a dozen degrees above Mars.
    You might be able to spot the last the naked-eye planet, Mercury, as early as Wednesday if you’re lucky. It will be even lower than Venus in the glow of the coming sun. You’ll likely need to scour the horizon with binoculars to first see this fleeting planet, which will present an easier target next week.

Believe it or not, winter’s here

As the sun sets, look in its wake for Mercury just above the southwest horizon. Binoculars will help. Mercury is on its way up to a fine showing through Christmas and New Year’s.
    Before dawn, Venus, Mars and Jupiter stretch above the horizon in the southeast. A little below Mars is Spica. Saturn rises just before the sun and is far to the lower left of Venus, so low that you may need binoculars to spot it.
    Tuesday at 11:48pm EST, the sun reaches its southernmost position in the sky, hovering directly over the Tropic of Capricorn at 231⁄2 degrees south latitude. This solstice, literally sun stands still, marks the start of winter for us in the Northern Hemisphere. The sun rises and sets at its farthest point south, traveling a low, shallow arch from horizon to horizon in the shortest day of the year, with a meager 9 hours 28 minutes of sunlight in Chesapeake Country.
    Watching the sunrise or sunset, you will notice the sun pause for a number of days, but then it slowly inches northward on the sky’s dome. A great experiment for kids of all ages is to use an east- or west-facing window to mark with a grease pen or piece of tape the point where the sun meets the horizon each day or night.
    Solstice coincides with the Ursid meteor shower, which typically peaks at five to 10 meteors an hour but occasionally has bursts of 100 or more. The waxing gibbous moon sets before dawn, so that’s when you’re likely to see the most activity.

The Geminids can really deliver

Dropping temperatures and long nights — combined with this week’s new moon — make for some of the best sky-watching. The sun still sets well before 5pm, and within another 90 minutes the sky is truly dark. Coupled with the darkness, the cold weather knocks any humidity from the air, providing crisp, undistorted views of the stars and planets.
    As evening twilight deepens, December’s sky is filled with familiar figures. To the west are the lingering constellations of summer, Aquila the eagle, Lyra the harp and Cygnus the swan, the brightest stars from each making the familiar asterism of the Summer Triangle. Cygnus is also known as the Northern Cross, as this time of year it stands upright above the horizon.
    To the north is the familiar shape of the Big Dipper, which is itself a part of Ursa Major, the great bear. Below it is the Little Dipper, host of the North Star Polaris, around which the entire celestial sphere revolves.
    High overhead is W-shaped Cassiopeia the queen and Cepheus the king, which looks more like a bishop’s miter than a king’s crown. Beneath them is their daughter Andromeda, flanked by the square of Pegasus to the west and the hero Perseus to the east.
    Rising in the east in the evening are the constellations of winter. There’s Taurus the bull, pursued by Orion the hunter, his hourglass shape one of the easiest to make out. Trailing Orion is Canis Minor, the Little Dog, and Canis Major, the Big Dog, home to Sirius, the brightest star in the Northern Hemisphere. Standing high over the east horizon by 10pm are the Gemini twins.
    Keep your eyes on those two this week, as they are the apparent source for the consistently best meteor shower of the year, the Geminids. There’s no interfering moonlight, and unlike other meteor showers, you don’t have to wait until the wee hours for the best of this show. This year’s peak, in the dark hours Sunday to Tuesday, can produce more than 100 meteors in an hour. The meteors can appear anywhere in the sky, but traced backward they all appear to radiate from Castor and Pollux in Gemini. By midnight this radiant is almost directly overhead.
    The Geminids are unique, in that their parent is the asteroid 3200 Phaethon, while all other meteor showers are spawned by comets. In either case, as these frozen interlopers near the sun in their orbit around the solar system, some of their matter melts off into bits of stellar debris that burst aflame as they carom into earth’s atmosphere.
    As daybreak approaches, Gemini is high in the west. By that time Jupiter, now rising around midnight, is high in the south, trailed by Mars and much closer to the horizon Venus in brilliant glory

The pre-dawn display in the east continues this week, with the waning crescent moon joining the show. Early Friday the moon trails Jupiter by just two degrees, with Mars, Spica and Venus stretching down to their left. Saturday, the moon is between Jupiter and Mars, while Sunday the moon hangs almost equally between Mars and Spica. Then Monday the moon shines barely one degree to the right of Venus, easily within the field of view of binoculars, a modest telescope or a camera. Tuesday you’ll be hard-pressed to spot the last of this thin crescent, now a dozen degrees below Venus. Venus, the brightest of all stars and planets, is sinking lower day by day, while Jupiter, Mars and Spica are climbing higher and rising earlier.
    We’re still a few weeks from the December 22 solstice, but Tuesday is our earliest sunset of the year.