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Articles by J. Alex Knoll

Let it guide you through the night

Friday evening, look in the wake of the setting sun low in the west-northwest for the nascent crescent moon and Mercury. Mercury is just a few degrees to the upper right, but both are so close to the horizon that you may need binoculars and you won’t have long. Within 90 minutes of sunset Mercury is gone. And that window is shrinking each day. Mercury is surprisingly bright — equal to any star. But don’t confuse its white glow with the much brighter and golden hue of Jupiter, 20 degrees higher.
    By sunset Saturday, the moon has climbed well above the horizon, leaving Mercury in the dusk. Now the thin crescent is just seven degrees below Jupiter, easily the brightest object other than the moon. The moon, Jupiter and Pollux higher still form a near-straight line.
    Sunset Sunday finds the waxing crescent moon well positioned in the west. Jupiter shines 10 degrees to its right, while below and to the left, making a wide triangle, is the first-magnitude star Procyon. The eighth-brightest star in the heavens, Procyon is one of two bright stars in the constellation Canis Minor, the Little Dog.
    Monday the moon is amid the dim stars of Cancer. Look a few degrees to the right of the moon for a dim patch of light at the constellation’s center. Unlike the sharp, clear light of a star, the hazy glow you’re seeing is the combined light of hundreds of newborn stars within the Beehive Cluster 570 light years away. While our own sun is 4.5 billion years old, the stars of the Beehive Cluster are only 600 million years old, mere infants in the life of a star. Binoculars are enough to distinguish dozens of these lights; a modest telescope reveals many more.
    Tuesday and Wednesday the moon is several degrees to either side of Regulus, the blue-white heart of Leo the lion. Regulus marks the dot at the base of what looks like an inverted question mark, called the Sickle of Leo.
    As twilight turns to darkness, Mars glows like an ember in the south. Far to the lower left is Spica. The red planet sets around 3am.
    Saturn shines in the southeast at sunset, is high in the south around midnight and sets in the west around 4:30am. The ringed planet is flanked by the two brightest stars of Libra — both second-magnitude — Zubenelgenubi and Zubeneschamali.
    In the hour before sunrise, Venus appears low in the east. At –4 magnitude, there’s no confusing the Morning Star for anything but an airplane or satellite — except that it holds steady in place until daybreak.

Hundreds of shooting stars possible this weekend

If you’re not a night owl, you’ll want to set your alarm clock for early Saturday. Before dawn that morning, earth will plow through the trail of a newfound comet, providing what many astronomers are predicting to be the best meteor storm in years.
    Comet 209P/LINEAR orbits the sun over a five-year period, yet it was only discovered in 2004 by the Lincoln Near-Earth Asteroid Research project. It belongs to a family called the Jupiter Comets, which are steered and propelled by the gas giant’s own gravitational pull. Every so often, these comets come a little too close to Jupiter, and like a leaf buffeted by the wind, their course is set anew.
    That’s what happened in 2012 to Comet 209P/LINEAR. Not only did it alter the comet’s path, but it also warped the centuries-old trails of debris left with every five-year passing. Now the comet’s path comes within 280,000 miles of our own orbit — little more than the moon’s distance from earth.
    Not that the comet will actually pass that close to earth. At its innermost point of orbit, 209P/LINEAR is 90 million miles from the sun — roughly the same distance from the sun as earth, give or take a few million miles. May 29 the comet will be just 5.15 million miles from earth, the ninth closest approach by a comet ever recorded.
    Even at its closest, it’s doubtful you’ll be able to spot this small, dim chunk of ice and rock without a decent-sized telescope.
    In this case the sizzle is far better than the steak, thanks to the countless bits of dust trailing in the comet’s wake after hundreds of years circling the sun. Between sunset Friday and dawn Saturday, earth plows full-steam through these bands of accumulated inter-stellar flotsam.
    Astronomers are predicting a brief but intense period of activity, peaking around 3am with anywhere from dozens to hundreds of meteors an hour. Some models even predict a meteor storm with as many as 400 meteors an hour! And unlike most prolific meteor showers, which streak past in a matter of seconds, those from P/209 LINEAR will drift through the sky like falling snowflakes.
    Cloudy skies? Check out the meteor shower via a live feed starting at 1:30am Saturday at http://tinyurl.com/olywq6k.
    The waning crescent moon won’t interfere with the meteors, but it will make a nice appearance with Venus low in the east before dawn Sunday morning.

And one bright, streaking light

As the sky grows dark, the first light you’re likely to spot is Jupiter high in the west, slipping toward the horizon and setting around midnight. Above it are Pollux and Castor, the two brightest stars in the constellation Gemini. Orange-hued Pollux is the 17th brightest star, and white-hot Castor is the 23rd brightest. But at magnitude –2, Old Jove is exponentially brighter.
    Mars is another easy target, appearing high in the south at dark and setting in the west around 3:30am. While it is no brighter than a strong star, its steady red glow stands out among the stars.
    You’ll have to hunt for Mercury amid the ashen light of sunset, when the innermost planet hovers within 10 degrees of the west-northwest horizon. Mercury reaches its farthest point from the sun on the 25th, when it appears 15 degrees above our horizon at sunset and remains visible for almost two hours. These next couple weeks are the best chance all year to see this elusive planet at night. On Tuesday and Wednesday nights look for Mercury between the two stars that mark the horns of Taurus the bull.
    As Mercury sinks toward the northwest horizon, Saturn rises in the southeast. The ringed planet is also making its best nighttime appearance of the year and shines overhead from dusk until dawn. Below it snakes the form of Scorpius punctuated by red-glowing Antares.
    Venus is brilliant as the Morning Star low in the east at dawn. It rises around 5am, and as daybreak nears it blazes from its perch 15 degrees above the horizon. Keep an eye on its leisurely climb and you can spot it shining through the glare of early morning.
    Another bright light pierces the darkness this week, as the International Space Station makes several good appearances. At its dimmest, the ISS rivals any star; at its peak, it can rival Venus. But while the stars and planets give you time to pause, the space station streaks by in a matter of minutes. Traveling 17,000 miles an hour, it orbits the earth every 90 minutes. Unlike the lights from a passing airplane, you aren’t seeing the lights aboard the ISS. Instead, hovering 250 miles over the planet, the station receives plenty of sunlight, which is reflected back to our eyes.
    Friday morning the ISS appears in the southwest at 5:16am, climbing toward the celestia zenith, then disappearing in the northeast at 5:20. Saturday it appears almost 30 degrees above the south-southwest horizon at 4:30am, climbs another 30 degrees, then vanishes three minutes later in the east-northeast. Tuesday the station appears almost directly overhead at 3:42am and shoots to the north before disappearing two minutes later. For more detailed sighting opportunities, visit http://spotthestation.nasa.gov.

Spread the joy of the night sky

The moon waxes through evening skies this week, reaching full phase Wednesday. Look for it just a few degrees to the west of Mars Saturday. The next night it is flanked with Mars to the right and Spica even closer to its left. Tuesday the near-full moon is five degrees to the right of Saturn and 10 degrees to the left Wednesday. The moon is so bright, you’ll have to hunt for the ringed planet.
    This is Saturn’s best appearance, as the planet reaches opposition, rising around sunset and remaining visible until daybreak.
    Jupiter is high in the southwest at sunset, the brightest nighttime object until the moon rises and an easy target until settnig around midnight. Castor and Pollux, the twins of Gemin, which actually appear quite distinct from one another, are just above Jupiter,
    If you have a clear view to the west-northwest horizon, look for Mercury emerging from the haze of evening twilight before setting itself shortly after 9pm. The planet is quite bright and grows more so in the coming nights, appearing higher each night through much of May.
    Venus is brilliant as the Morning Star low in the east during dawn. With binoculars or a small telescope, look to the upper left of Venus for distant Uranus, which is only two degrees away Thrusday the 15th.
    Saturday marks spring Astronomy Day, an annual event begun by California astronomer Doug Berger in 1973. The idea began with astronomers setting up telescopes in busy urban locations so that city-dwellers could be introduced to the joys of the night sky. Now it’s commemorated around the world by friends and family gathering to exploring the heavens together.

You don’t have to wait until 2061 to delight in its offspring

A thin sliver of the waxing crescent moon rises Thursday evening just after sunset, its tips pointing almost straight up. Look a few degrees below its outside curve for Aldebaran, the orange eye of Taurus the bull. High above the moon is Jupiter, shining brighter than any star-like object.
    Friday evening the moon has halved the distance from Jupiter, which is 20 degrees — two fist-widths held at arm’s length — straight up. To the moon’s left is Betelgeuse, the shoulder of Orion. Far to the south is Sirius, the brightest star. Sunset Saturday reveals the growing moon just 10 degrees below Jupiter in the west. Betelgeuse is almost equidistant below the moon. By Sunday, the moon is less than 10 degrees to the south of Jupiter.
    Far to the east of Jupiter is Mars. Shining at magnitude –1.2, the red planet is brighter than any star except Sirius. Compare it to Spica, in the constellation Virgo, 10 degrees to the east. At 11pm Mars is at its highest and is due south. It sets around 4:30am.
    Saturn, the dimmest of the naked-eye planets, trails well behind Mars. But as the ringed planet nears opposition May 10, it puts on its best face. Look for it rising in the east around sunset, a steady golden glow amid the much dimmer stars of Libra. The rings are opened at roughly a 20-degree angle, and are easy to discern in even a modest telescope.
    As the darkness begins to fade, Venus rises in the east, blazing at magnitude –4.2. The Morning Star is so bright that you can still find it in the east an hour after sunrise.
    If you’re up waiting for Venus, you may spot a streak of light crossing the heavens. This is the annual return of the Eta Aquarid meteor shower, which peaks Monday and Tuesday. This should be a good showing, as the first-quarter moon sets just after midnight. The meteors appear to emanate from the constellation Aquarius, but they can appear anywhere on the celestial dome. The best viewing is in the nether hours between midnight and dawn, when it could rain up to 30 meteors an hour. While not likely to produce a great storm, the Eta Aquarids are steady, stretching out a couple weeks before and after the peak.
    Twice a year the earth passes through a stream of debris left in the wake of Halley’s Comet. While the famed comet only visits the inner solar system every 75 years, it has been doing so for millennia, leaving ring upon ring of jetsam with each passing. These countless bits of ice and dust date to the formation of the solar system, and as earth plows into them, they ignite upon contact with our atmosphere. At the other side of the sun, earth crosses Halley’s path again in the fall, resulting in the Orionid meteor shower.

This pollution is endangering our night skies

We all know of Earth Day, but what about Dark Sky Week?
    “I want people to be able to see the wonder of the night sky without the effects of light pollution,” says Jennifer Barlow, who came up with the idea of Dark Sky Week as a high school student in 2003. “The universe is our view into our past and our vision into the future … I want to help preserve its wonder.”
    We’re in the midst of this celebration of darkness, which has grown into a global movement, leading to downward-facing streetlights, low-glare outdoor bulbs and a greater understanding of the value of darkness.
    “Once a source of wonder — and one-half of the entire planet’s natural environment — the star-filled nights of just a few years ago are vanishing in a yellow haze,” warns the website for Dark Sky Week’s parent organization, the International Dark-Sky Association. “Human-produced light pollution not only mars our view of the stars; poor lighting threatens astronomy, disrupts ecosystems, affects human circadian rhythms, and wastes energy to the tune of $2.2 billion per year in the U.S. alone.” Learn more at www.darksky.org.
    Find your piece of darkness and a view to the east before daybreak Friday and Saturday, when the waning crescent moon hovers within 10 degrees of dazzling Venus.
    Tuesday’s new moon provides the backdrop for this week’s installment of the Globe At Night campaign, which fits hand-in-glove with Dark Sky Week. Your fisthand sightings help map what’s visible — and not — in the night sky all around the world. It’s easy to take part. Log onto www.globeatnight.org to download a star map of Leo the lion, see how many and which of the stars you can spot on a clear night, and return to the website (or the mobile app) to upload your results.
    For parts of South Africa, Australia and Antarctica, Tuesday’s new moon lines up just right between the earth and sun to create an annular solar eclipse. In an annular eclipse, the moon is too far from earth to fully obscure the sun, instead covering only the corona and creating a ring of light outlining the darkened moon. While you’ll likely have to settle for on online view of this one, we’ll have front-row seat for October’s partial solar eclipse.

Bright planets and shooting stars dazzle this week

As the sun sets, Jupiter shines high in the southwest, smack-dab in the middle of the constellation Gemini, its bright stars Castor and Pollux a few degrees away toward the celestial zenith. By midnight the king of the planets hovers above the horizon and sets within another hour.
    By that time, Mars is high in the south. Just days past opposition, the red planet is visible from dusk until dawn. It is also at its closest to Earth in six years. If you have a telescope, you’ll want to aim it at our planetary neighbor, which won’t appear so large in a view-piece again for two years. Mars shines in the constellation Virgo, with its blue-white alpha star Spica trailing by 10 degrees. As daybreak arrives, they are low against the west horizon.
    In the hour before sunrise, Venus dominates the east, brighter than anything but the sun and moon. The Morning Star doesn’t climb high above the horizon, which only adds to its splendor as its light shimmers and sparkles like a kaleidoscope as it passes through Earth’s atmosphere.
    The dark hours between Tuesday and Wednesday mark the peak of this year’s Lyrid Meteor Shower. The best viewing is between midnight and daybreak, when you might spot up to 20 meteors an hour, some with long trails burning for several seconds. The waning crescent moon rises around 3am and could dampen the showing. But keep your eyes peeled through the week when errant meteors could still streak across the sky.

Bright planets and shooting stars dazzle this week

As the sun sets, Jupiter shines high in the southwest, smack-dab in the middle of the constellation Gemini, its bright stars Castor and Pollux a few degrees away toward the celestial zenith. By midnight the king of the planets hovers above the horizon and sets within another hour.
    By that time, Mars is high in the south. Just days past opposition, the red planet is visible from dusk until dawn. It is also at its closest to Earth in six years. If you have a telescope, you’ll want to aim it at our planetary neighbor, which won’t appear so large in a view-piece again for two years. Mars shines in the constellation Virgo, with its blue-white alpha star Spica trailing by 10 degrees. As daybreak arrives, they are low against the west horizon.
    In the hour before sunrise, Venus dominates the east, brighter than anything but the sun and moon. The Morning Star doesn’t climb high above the horizon, which only adds to its splendor as its light shimmers and sparkles like a kaleidoscope as it passes through Earth’s atmosphere.
    The dark hours between Tuesday and Wednesday mark the peak of this year’s Lyrid Meteor Shower. The best viewing is between midnight and daybreak, when you might spot up to 20 meteors an hour, some with long trails burning for several seconds. The waning crescent moon rises around 3am and could dampen the showing. But keep your eyes peeled through the week when errant meteors could still streak across the sky.

Luna joins several luminaries, but its disappearing act is the best

The moon waxes through the weekend, until Tuesday’s full moon, known as the Grass Moon, the Egg Moon and the Pink Moon. This is also the first full moon since vernal equinox, the Paschal Moon, marking the start of Passover and setting the date for Easter the following Sunday.
    Thursday the bright gibbous moon hovers below the first-magnitude star Regulus, heart of Leo the lion. Stretching up from the star like an inverted question mark is the Sickle of Leo, which marks the head of the celestial lion. Located along the ecliptic — the pathway through the heavens of the sun, moon and planets — Regulus is joined every month by the moon, which is never more than five degrees away.
    The following nights the moon marches eastward against the backdrop of stars, leaving Leo and approaching Virgo. By Saturday it is in a barren patch of sky, midway between Regulus and equally bright Spica to the east. Don’t confuse Spica’s blue-white glow with that of ruddy Mars a few degrees away.
    By Sunday, the moon forms an uneven triangle with Mars and Spica, its shape shifting as the three objects pivot to the west. Monday the near-full moon is within five degrees of Mars — and about half that distance from Spica. The three are so close that they will all fit within the field of view of binoculars or telescope. Come Wednesday, the moon comes within a few degree os Saturn amid the faint stars of Libra.
    Tuesday, the full moon rises as the sun sets and sets the next morning at sunrise. But in between, a little before 1am, the moon slowly inches behind earth’s full shadow, or umbra, in a total lunar eclipse. The eclipsed moon never actually disappears, but it does darken considerably, sometimes taking on a coppery or even blood-red hue as if illuminated from within. While the hours are for night owls, we’re in prime position to see this along Chesapeake Bay (as is most of North and South America as well as Australia). Unlike an eclipse of the sun, you can stare at this all you want with no worries.
    Beginning around 1am, the moon crosses into earth’s outer, or penumbral, shadow. The change is slow and subtle, with the moon’s left, or northwest, edge starting to darken ever so slightly. But by 2am, as the moon slips behind the umbral shadow, the darkness spreads and deepens. The total phase begins at 3:07am, and at 3:46 the moon, earth and sun will be almost perfectly aligned, with the moon appearing as an eerie shadow of its usual self. Totality ends at 4:25am, and by 5:33 the moon will have crept from the umbral shadow. As daybreak draws near, the moon escapes earth’s shadow, only to set in the west.

Winter’s constellations are on the way out, while spring’s are here to stay

As the sun sets Thursday evening the waxing crescent moon appears high in the south, its lower tip pointing to the star Aldebaran a few degrees away. Aldebaran is a red-giant that marks the eye of Taurus the bull. Just to the left of the moon is the Hyades cluster, a V-shaped pattern of stars that make up the face of the bull. Higher above the moon is the Pleiades cluster, marking the bull’s shoulder. Named after the seven daughters of Atlas, six of the mythological sisters are visible to the naked eye. How many can you spot?
    Saturday the moon shines near Jupiter, the next-brightest object in the night sky. The Gemini twins Castor and Pollux are above Jupiter, while below the moon is the bright orange star Betelgeuse, the shoulder of Orion. The next night the waxing moon is just a few degrees below Jupiter, well within the field of view of binoculars. Surrounding the moon and Jupiter are the bright stars of the Great Winter Circle (which looks more like a hexagon): Aldebaran, Rigel, Sirius, Procyon, Pollux, Castor and Capella. Within the circle is Orion’s bright-red star Betlegeuse. This is the last month to catch these winter luminaries as they shift to the west and out of sight.
    While Jupiter fades with the stars of winter, Mars is at its prime amid the stars of spring. The red planet appears low in the east at sunset with the blue-white star Spica five or six degrees to its lower right. Mars reaches opposition on the 8th, at which point it rises as the sun sets and does not set until sunrise the next morning. This is its best apparition all year, and only Jupiter and Venus shine brighter.
    Saturn rises in the southeast around 10:30pm, is at its highest in the south around 3am and is low against the southwest horizon at daybreak. The planet is tilted in such a way that its rings are on full display with even a small telescope. The ringed planet is in the middle of Libra and forms a tight triangle with the constellation’s two brightest stars. To the west of Saturn and marking the balance’s fulcrum is Zubenelgenubi, while above the planet and marking the upper scale is Zubeneschamali, which has the distinction of being the only star that glows with a green hue. Not everyone can distinguish the color; can you? Zubenelgenubi is Arabic for the southern claw, while Zubeneschamali translates to the northern claw, namesakes from when these stars were part of the constellation Scorpius.
    The last of the planets visible this week rises before dawn. There is no mistaking Venus above the southeast horizon shining at magnitude –4.5, exponentially brighter than even the brightest star. Venus doesn’t climb very high, but it will hold this position in the early morning through spring and summer.