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Articles by J. Alex Knoll

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.

Help plot the stars and shine a light on light pollution

With the moon waning through pre-dawn skies, this week marks the year’s second Globe at Night backyard observing drive, which aims to enlist you in charting the night sky. The goal: “to raise public awareness of the impact of light pollution by inviting citizen-scientists to measure their night sky brightness and submit their observations to a website from a computer or smart phone.”
    This month’s target constellation is Orion. To get started, log onto the Globe at Night website — www.globeatnight.org — where you’ll find star charts of Orion custom-tailored to your viewing area. Then, find a dark location and see how many stars you can spot compared to those shown on the charts. Finally, upload your results on the website or through the Globe at Night smart-phone app. You can make and tally as many observations as you like from the same or several locations. Based on the results, astronomers can gauge the effects of light pollution across the earth.
    Sunset reveals Jupiter high overhead. Shining at the feet of the Gemini twins Castor and Pollux, Jupiter rules the heavens in brightness for much of the night.
    Saturn is on prime display by midnight, and Thursday it should be all the easier to spot as it travels within a few degrees to the left of the moon. The moon and Saturn remain together through the night, and by dawn Friday you can find them low in the south. Farther to their right are Mars and Spica.
    If you’re up before dawn and have a clear view to the east, you’ve probably noticed the morning star Venus. Blazing at magnitude –4.9, Venus is at its brightest of the year. Wednesday, ­Venus is joined by the thin crescent moon just to the left. The two are just as close before dawn Thursday the 27th.

This nebula is alive with stars

As the sun sets, one of the first constellations to appear is Orion, already high in the southeast, and by 8pm looming in the south. With its geometric, hourglass shape, Orion is one of the easiest constellations to spot and one of the most rewarding to study. The brightest star is blue-white Rigel to the lower right, marking the hunter’s left knee. Opposite to the upper left is the red-giant Betelgeuse, punctuating Orion’s raised right arm.
    Marking the hunter’s opposite shoulder is Bellatrix, meaning female warrior. While nowhere near as bright as Rigel or Betelgeuse, Bellatrix is still the 22nd brightest star. Juxtaposed to the constellation’s lower left and marking the hunter’s right knee is Saiph, bright enough to stand up to the glare of this week’s bright moon.
    Perhaps even more recognizable are the three almost perfectly aligned stars of Orion’s belt, Alnilam, Mintaka and Alnitak. The belt points down toward Sirius in Canis Major, the brightest of all stars. Following the belt the other direction leads to Taurus the bull and its red-orange star Aldebaran.
    Hanging perpendicular from the belt is another, fainter line of stars that forms Orion’s sword. One of the objects in the sword isn’t a star at all but rather a blazing and massive illuminated cloud of stellar gas, the Orion Nebula, or M42. At 1,400 light years distant, the Orion Nebula shines at fourth magnitude, appearing as a fuzzy patch to the unaided eye. Binoculars reveal M42’s light as distinct stars, while even a modest telescope hints at the vast number of stars lurking within the clouds. But what really stands out is the luminosity as opposed to individual points of light. Nestled within the clouds like a celestial incubator are thousands of nascent stars, their light diffused and spread through the gas.
    The beacon of light above Orion is Jupiter. It is visible all night before finally setting in the northwest around 4am. Mars rises around 10:30pm and is high in the south around 3am. Saturn rises after midnight, well to the left of Mars and high in the south with dawn. By that time Venus is well positioned above the east horizon, having risen around 4:30. There’s no missing this morning star, unless you mistake it for a plane or some other unidentified flying object.

Now Playing In the Sky Near You

Winter, spring, summer or fall, there’s always a blockbuster overhead on any clear night.
    Mercury still clings to the west-southwest horizon a half-hour or so after sunset at week’s end. It is surprisingly bright, but you may need binoculars to pick it out amidst twilight’s glare. Catch this one while you can, as it’s on its final showing.
    Sunset finds Jupiter high in the east, easily the brightest nighttime object other than the moon, which pays the gaseous giant a visit early next week. Whereas Earth has but one moon, the king of planets has more than 60 moons, four of which you can see through a small telescope or even binoculars. Io and Europa are roughly the size of our moon, while Callisto and Ganymede are half again as large. In fact, Ganymede is larger than Mercury.
    By 9:30pm, Jupiter is almost directly overhead, surrounded by The Great Winter Circle, an asterism of seven of the 25 brightest luminaries. Just to the east of Jupiter are the Gemini twins Castor and Pollux, the 23rd- and 17th-brightest stars respectively. Shifting your gaze clockwise to the north you’ll find golden Capella, the sixth-brightest star. Continuing now to the southwest, look for Aldebaran, the red eye of Taurus the bull, the 14th-brightest star. From there, look to the south for Rigel, the foot or Orion the hunter and the seventh-brightest star. You’ll find the brightest star of all, Sirius of Canis Major, at the southern edge of the circle, followed to the east by Procyon of Canis Minor, the 8th-brightest star. Within the Circle but not part of the actual asterism is the 11th-brightest star, Betelgeuse, marking Orion’s shoulder. The waxing gibbous moon is also within the Circle throughout much of this week.
    Mars rises around 11pm and is less than five degrees from Spica, the 16th-brightest star in the heavens. As daybreak nears, the two are high in the south. Trailing behind the two and rising 90 minutes later is Saturn, a steady golden light as bright as the average star.
    Finally, in the hour before sunrise, the brightest star-like object crests the southeast horizon. Nothing aside from the sun and moon outshines Venus, which is at its most brilliant this week, although it will remain a fixture in our pre-dawn skies until autumn.

A recent solar flare could present Northern Lights to Southerners

A powerful solar flare on January 7 launched a barrage of plasm our way, which has the chance of producing auroras at much lower latitudes than usual. Scientists expect the activity to begin before dawn Thursday, January 9, which is too late to help given this issue’s release that day. But solar astronomers don’t rule out more blasts to come, as this solar flare, technically called a coronal mass ejection, was caused by an eruption from a massive and very active sunspot, AR1944, which is facing earth head-on. The sunspot, “as wide as seven earths,” NASA reported, is “one of the largest sunspots seen in the last 10 years.”
    Called aurora borealis when seen north of the equator and corona borealis to the south, these displays are the result of powerful bursts of radiation from the sun. Earth’s atmosphere blocks that harmful radiation, or these would be lethal events, but as the charged particles collide with earth’s own magnetically charged atmosphere, they produce a vivid and eerie light show. While these aurora are harmless to life, they can wreak havoc on our satellites, disrupting GPS, cellular reception and radio and television transmissions. The flare has already forced private space company Orbital Sciences to delay the launch of an unmanned cargo craft to the International Space Station.
    Any chance to see the so-called Northern Lights as far south as the Chesapeake is well worth keeping an eye on the sky over the next few nights.
    The moon is also busy this week. It visits over the weekend, to the left of the moon Friday night, look for the Pleiades star cluster. At first glance the Pleiades appear as a fuzzy patch of light in the constellation Taurus. But closer examination on a clear night reveals six stars shaped like a miniature dipper.
    Saturday the Pleiades are above the moon, while below the moon is Aldebaran, the red eye of the bull, and the Hyades star cluster.
    On Tuesday, the near-full moon is five degrees south of Jupiter. Tuesday, January 7, marked the anniversary of Galileo Galilei’s 1610 discovery of Jupiter’s largest three moons,  Io, Europa and Ganymede (he discovered Callisto a few days later). Today, a good pair of binoculars will reveal more of mighty Jove’s orbiting satellite’s than the great astronomer’s first telescope.
    Wednesday the 15th marks January’s full Wolf Moon, which also reaches apogee, its farthest point in orbit from earth, making this full moon the smallest of the year.
    Venus reaches inferior conjunction, Saturday, passing between the earth and sun, leaving our morning skies only to reappear as the Evening Star thereafter. Unlike the transit of Venus in 2012, this time Venus will pass five degrees north of the sun — still far too close to watch without a solar filter. Viewed with telescope or binoculars and the proper eye protection, our sister planet appears as a wide but razor-thin crescent.

Our closest approach to the sun does make for the shortest season

Twilight Thursday and Friday evening reveals the new crescent moon low in the southwest with Venus blazing a few degrees away tight against the horizon. Venus sinks lower in the early evening sky over the next week, finally disappearing between the sun and earth on January 11. Then, after a few days absence, it reappears in pre-dawn skies, where it will blaze as the Morning Star until autumn.
    Moonless skies provide a dark backdrop for this year’s Quadrantid meteor shower, which is at its best in the wee hours before dawn Friday and Saturday. Best viewing will be from a dark location after midnight. Meteors will radiate from the constellation Boötes, but can appear anywhere in the sky. The Quadrantids can produce from 50 to 100 meteors an hour, but timing — or more aptly, luck — is essential, as this shower peaks within just a few hours, and then it’s over.
    You shouldn’t have any trouble spotting Jupiter, which reaches opposition Sunday, when it will shine in our night skies from sunset until sunrise, far brighter than any star. At opposition, the gaseous giant is its closest to earth and farthest from the sun, with earth right between the two.
    Mars rises around midnight and is high in the south as daybreak approaches. Far below the red planet is Saturn, actually a little brighter but harder to see so tight against the horizon.
    Saturday, earth reaches its closest point to the sun for the year — called perihelion. At that point the sun is roughly 3 million miles closer to the sun than it is at aphelion in July. While 3 million miles may seem like a lot, the distance has little correlation with the change of seasons, which are a result of earth’s 231⁄2-degree tilted axis. It does, however, affect the length of the seasons, since when the earth is nearest the sun it is also traveling its fastest — more than three percent faster than at aphelion. As a result, the seasons come and go quicker this time of year, with the time between December’s solstice and March’s equinox almost five days shorter than from June’s solstice until September’s equinox. As a result, winter is the shortest season for those of us in the Northern Hemisphere.
    Saturday, two weeks after solstice, is the latest sunrise of the year. Sunrise comes a few seconds earlier than the day before, and while the change will be subtle at first, by the end of the month the sun will rise more than 10 minutes earlier than it does now.

The interloper visits Spica and Mercury

Mercury is putting on its best pre-dawn show of 2013, more than doubling in brightness this week, from +1 magnitude to –0.5 (each order of magnitude is exponential, so an increase from +1 to 0 is a doubling). Monday marks the innermost planet’s greatest elongation — its farthest point away from the sun as seen from earth and its highest point above the horizon. Mercury rises a little before 6am and climbs nearly 15 degrees above the southeast horizon before the sun rises more than an hour later. Ten degrees above Mercury is blue-white Spica, but even this first-magnitude star pales compared to Mercury this week.
    First discovered last September, Comet ISON is heading into the inner solar system for the first time, coming within 700,000 miles of the sun November 27. If the comet survives that close encounter, it could live up to the comet of the century billing. If not, the next two weeks are your best chance to spot this long-distance traveler.
    With binoculars or a small telescope, look for ISON one degree to the west of Spica Sunday before dawn and less than one-half degree to the east of the star the next morning. By next Thursday and Friday, ISON will be within 10 degrees of Mercury — well within your binoculars’ field of view. Perhaps by then it will be bright enough to see with the unaided eye.
    Sunday marks the full moon, the Beaver Moon and the Frost Moon according to lore. The full moon floats just six degrees below the miniature dipper-shape of the Pleiades star cluster, while Monday night it is even closer to Aldebaran, the red eye of Taurus the bull.
    The full moon’s glow washes out all but the brightest meteors in this year’s Leonid shower, which peaks between the 16th and 18th. Still, the Leonids are active through the month, so patience or luck will likely reward you with a few of these shooting stars.

July brings the first of three Super Moons

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