view counter

Articles by J. Alex Knoll

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.

Countless specks form the Zodiacal Light

The waning crescent moon ends the week low in the southeast before dawn. Sunday marks the new moon, the second in March. But it’s not gone long, reappearing as a thin sliver above the western horizon at sunset on the 31st.
    With the moon out of sight much of the night, this week provides one of the best chances to see the zodiacal light, a hazy glow that extends like a cone from the western horizon pointing heavenward also called false dawn. It appears an hour or two after sunset, and you’ll only see it with clear, dark skies.
    If you see the zodiacal light, you might first think you’re looking at a wispy cloud, back-lit by starlight. Or maybe the Milky Way. But its opaque, pyramid-shaped glow extending up from the horizon is unique.
    What you’re seeing are tiny bits of matter floating between the sun and earth. Left over from the formation of the solar system 4.5 billion years ago, they range in size from meters to millimeters. Like everything else in the solar system, these micro-worlds orbit the sun, following the same path along the ecliptic as the other planets. And like the planets, they are not themselves luminous. What we see is sunlight reflected back to our eyes. None of these pieces of solar system detritus are large enough to reflect enough light to be seen from earth, but collectively they create this distinct glow that we see after sunset in late winter and early spring.
    While you’ll have to hunt for the zodiacal light, Jupiter is not nearly so elusive. In fact, the king of the planets rules the heavens from sunset, when he is almost directly overhead, until 2:30am, when he sets in the west-northwest. In that time, there is no brighter object visible.
    Mars rises around 9:30 and is easily spotted well above the horizon an hour later. Normally Mars shines about as bright as the average star. Not so right now, when the red planet easily outshines blue-white Spica five degrees to its lower-right. Mars glows a distinct orange-red and is almost as bright as it ever gets — almost. Watch over the next coming nights as the red planet climbs higher and glows brighter on its way to opposition April 8.
    Saturn rises before midnight, but your best view of the ringed planet is before dawn, when it is high in the south. It’s far to the left of Mars and not near so bright. The nearest bright star to Saturn is Antares, the red heart of Scorpius to the south.
    Venus rises an hour ahead of the sun. While this Morning Star doesn’t climb high above the horizon, it blazes at –4.5, exponentially brighter than any star.
    The pre-dawn window to see Mercury is closing fast. It trails Venus by about 20 degrees and is tight against the east-southeast horizon a half hour before sunrise.
    As if preparing for a final bow before leaving the stage, Orion stands over the southwestern horizon at sunset. This week is your last chance to observe the great hunter in the Globe At Night campaign. Come the end of April, Leo will become the focus in this effort to plot light pollution around the planet. For more information go to www.globeatnight.org.

As the sun perches over the equator, spring begins

Perhaps you’ll be at lunch Thursday at 12:57pm. Or maybe you’ll be busy at work or school. At that particular time, however, the sun shines directly above the equator. That morning it rises due east, and that evening it sets directly west. This is the vernal equinox, the first day of spring for the 90 percent of the world’s population living in the Northern Hemisphere. In the Southern Hemisphere, it is the first day of fall. Regardless of where you live, your day will be more or less split equally between daylight and night.
    More or less, because the earth is not a perfect sphere, it is tilted at a 231⁄2-degree angle, and its orbit around the sun is not a true circle. As a result of all this imperfection, our day of equal night and day along Chesapeake Bay was Monday, March 17. From now until the autumnal equinox in September, our days will boast more light than darkness, and our sunlit hours will continue to grow until summer solstice 13 weeks hence.
    The waning moon rises a little before midnight Thursday, with golden Saturn just two degrees ahead of it. As the two shift to the west, Saturn pulls farther away, but they are still within a binoculars’ field of view high in the south at 4am Friday. Early morning Saturday the moon is less than 10 degrees above Antares, the red-glowing heart of Scorpius, the celestial harbinger of spring. By Thursday the 27th, the thin crescent moon rises just 90 minutes before the sun and is accompanied by brilliant Venus less than three degrees below.
    Each year as Scorpius rises in the east, Orion sets in the west. At 9pm he is high in the southwest, but by midnight the hunter already has one foot beneath the horizon, and each night he marches farther from our view.
    So for one last time, Orion is the focus of this year’s Globe at Night Campaign, an international effort to involve ordinary sky-watchers like yourself in gauging the darkness of the night sky. This session runs from March 21st through the 30th. The data help determine the effects of light pollution. Thousands of observers from all over the world have already compared their own sightings to those on the supplied star charts and uploaded their findings to the group’s website: www.globeatnight.org. Now’s your chance to join the cause.

Five planets and a full moon grace our skies this week

With our return to Daylight Saving Time, I wake greeted by Venus blazing in the southeast. The Morning Star rises around 5:30, and an hour later it is well perched above the horizon, shining brighter than any object other than the moon and sun. As sunrise nears and if the sky is clear, another bright light appears 20 degrees in Venus’s wake, Mercury.
    Friday marks the innermost planet’s greatest western elongation — its farthest point from the sun as seen from Earth. Even so, it only climbs 10 degrees above the south-southeast horizon before sunrise. While Mercury doesn’t climb any higher, it brightens from +0.8 to –0.1 magnitude through March.
    Evening brings the other five naked-eye planets into view. As twilight gives way to darkness, Jupiter pops alight almost directly overhead. It is easily the brightest object other than the moon, which is far to the east this week.
    Mars rises around 9pm, as bright as any star. Compare its ruddy hue to the first magnitude star Spica’s blue-white glow just a half-dozen degrees away. Planet and star are at their highest in the south around 3am.
    By that time, Saturn is well above the southeast horizon, trailing 30 degrees behind Mars and Spica. The ringed planet is at its highest in the south a couple hours before sunrise.
    The moon is prominent this week, reaching full phase Sunday. Native Americans called this the Worm Moon, as this is the time of year when the ground softens and these creatures
begin to work the earth.
    Friday the waxing gibbous moon is just a few degrees to the west of the star Regulus in the constellation Leo, while Saturday the moon shines well below Regulus.
    Monday the just-full moon rises with Spica in tow. The lead star of Virgo stands almost directly below Luna, while ruddy Mars is just a few degrees left of Spica.
    Tuesday the moon, Mars and Spica rise in the southeast around 10pm and form a triangle. The waning gibbous moon shines four degrees to the lower right of Mars and one degree to the lower left of Spica. They remain tight all night and are high in the northwest as sunrise approaches Wednesday morning.

The earth’s pulse is quickening

Despite our recent snowy, cold spell, signs of spring are everywhere as the earth awakens from its winter hibernation. Long ago, the Celts of pre-Christian western Europe called this time of year the quickening. To them, all objects of Earth — not just creatures, but trees, stones and the ground itself — were alive, all sharing the same sap of life. Now, deep within the still-bare trees, the sap of life flows, birds build new nests; shoots of the earliest spring flowers pierce the frozen soil. All around us, the earth’s pulse is picking up its pace.
    These last weeks before the vernal equinox bring some of the greatest seasonal changes. Perhaps most noticeable is the growing length of daylight. Since solstice, December 21, we have gained more than an hour of sunlight in both the morning and at day’s end. Now, as the earth reaches an apex in its elliptical orbit around the sun, the days grow longer all the faster, adding another 20 minutes of sunlight in the morning and nearly 15 minutes in the afternoon between now and equinox March 21.
    Overhead, too, the changing constellations foretell the coming of spring. The familiar shape of Leo the lion crouches over the eastern horizon, its blazing heart, Regulus, piercing the darkness. Following the great lion is Virgo, the goddess of crops and harvest, holding in her hand an ear of wheat in the form of the brilliant star Spica.
    Behind those two zodiacal constellations is Boötes, the herdsman of Ursa Major and Ursa Minor. In Greek legend, Boötes is Arcas, son of the nymph Callisto and Zeus and the first to tie a team of oxen to plow, revolutionizing farming and ushering in the era of agriculture that led to the rise of civilization. Each year, Boötes returns to our evening skies to usher in the spring planting season.
    All five planets grace our darkened skies this week, with Jupiter appearing at sunset followed by Mars and Saturn later in the evening. Venus rises in the east around 4am — 5am with Sunday’s implementation of Daylight Saving Time. And Mercury glimmers low in the east-southeast during dawn, far to the lower left of Venus.
    Thursday, March 6, the moon nears the constellation Taurus and its first-magnitude star Aldebaran, which is to the upper left of the moon.The Pleiades star cluster is to the upper right of the moon, while the bull’s V-shaped face, the Hyades, is farther to the upper left of the moon. Friday night the moon is just two degrees above Aldebaran, which is roughly the width of a finger held at arm’s length.
    Sunday and Monday nights, the waxing gibbous moon joins bright Jupiter. Farther below the moon is the first-magnitude star Procyon of Canis Minor, the Little Dog.
    Daylight Saving Time begins at 2am Sunday morning, when we spring forward an hour. While we’ll lose an hour’s sleep in the morning, it will provide a reprieve for night-time sky-watching.
    The International Space Station races across our predawn skies. Tuesday it appears above the south-southwest horizon at 6:43am and arcs to the east-southeast horizon before setting at 6:46am. Thursday, March 13, it appears in the southwest at 6:40am and sets six minutes later in the northeast. It’s brighter than any star and moves faster than a jet.

The Dog Star’s neighbor once shined almost as bright as Venus

The Globe at Night campaign continues through the end of the month, so you still have a chance to contribute to this stellar effort. “Citizen scientists” — that’s you and me — are asked to study the constellation Orion and upload your sightings to the organization’s web site. Find details at www.globeatnight.org.
    The hunter’s neatly aligned belt stars point almost straight down to the brightest star in the heavens, Sirius in Canis Major, the Great Dog. A Greek-rooted word, Sirius means sparkling and scorching. The ancient Egyptians worshiped this star as their god, the dog-headed Anubis.
    Marking the dog’s forward paw is the constellation’s third-brightest star Mirzam, meaning the announcer in Arabic, as this star rises just before Sirius.
    The second-brightest star in Canis Major is Adhara, marking the great dog’s loin. Five million years ago, Adhara was a mere 34 light years away, and it blazed at –4 magnitude — nearly as bright as Venus! Seen from earth, no other star has ever shone so bright except our own sun. Since then, Adhara has raced from us and is now some 430 light years away and shines at a still-respectable magnitude 1.5.
    Less than five degrees directly below Sirius is the open star cluster M41, named after the 18th century French astronomer Charles Messier, who catalogued the night sky’s brightest objects. With today’s light-drenched skies, M41 appears as a single point of light. But that wasn’t always so. Around 325 BC, Aristotle wrote: “one of the stars in the thigh of the Dog had a tail, though a dim one: if you looked hard at it the light used to become dim, but to less intent glance it was brighter.”
    Staring at a point in the darkened sky, you’ll see what the Greek philosopher meant. Gaze straight at a star, and it dims. Look at it out of the corner of your eye, however, and the same star appears noticeably brighter. This is because our eyes have two distinct light-recognizing cells: Rods and cones. When we stare intently at something, the cone cells to the center of our retina react, providing us detail and color. However, in dim lighting, the rods at the retina’s outer edge respond.
    Today astronomers know that M41 is in fact hundreds of stars, but if you hope to see more than one point of light in this cluster, you’ll need binoculars or a modest telescope.