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Regulars (Sky Watch by J. Alex Knoll)

The equinox ushers in fall

Week’s end finds the waning crescent moon in the company of Jupiter before dawn. Around 6am Friday morning, look for the moon high in the east with Jupiter to its lower left. The same time Saturday the moon shines just six degrees from Old Jove. Then Sunday, the now razor-thin crescent is well below Jupiter, while the first-magnitude star  Regulus, is just six degrees away.
    While you should have no trouble spotting the waning crescent moon and Jupiter in the east before dawn, Venus is a trickier target. This Morning Star rises less than an hour before the sun, and that window of visibility shrinks by about a minute each day.  At best Venus is only 10 degrees above the horizon before sunrise, so you may need to scour the eastern skyline with binoculars to pinpoint Venus’ otherwise dazzling glow.
    This time of year before dawn offers the best chance to spot the eerie zodiacal light also called false dawn. You need dark skies away from any urban glare to see the zodiacal light, which glows like milky pyramid of light rising from the horizon an hour or two before actual dawn.
    Unlike true dawn, the zodiacal light is a pale, ghostly glow devoid of the rosy tint from the coming sun, which is caused by light entering earth’s atmosphere. The zodiacal light is actually sunlight reflecting off countless bits of dust and detritus within our solar system that orbit the sun along the same path as the planets. This time of year the ecliptic — the path of the sun, moon and planets — stands nearly straight up with respect to the eastern horizon before dawn.
    At the other end of darkness, Mars and Saturn shine low in the southwest in the early evening. Of the two, Saturn is slightly brighter and is farther west, setting around 9:30pm. Mars isn’t far behind, setting shortly after 10. But while the ringed planet is weeks away from disappearing amid the glare of the sun, Mars remains a fixture in our early evening skies for weeks to come.
    A clear view to the west-southwest immediately following sunset may reveal Mercury burried in the horizon. Binoculars will help, but don’t confuse it with nearby Spica, which is only a couple degrees away through the weekend. They are so close that both will appear in the same field of view using binoculars or a telescope.
    Monday at 10:29pm EDT, the sun is poised directly above the equator somewhere in the vicinity of New Guinea. On that day or the following, the sun rises due east and sets due west, dividing the day between near-equal amounts of daylight and darkness for everyone around the globe. For the 90 percent of us living in the Northern Hemisphere, this equinox marks the beginning of autumn.
    Because of the earth’s 231⁄2-degree tilted axis, the Northern and Southern Hemispheres each receive more direct sunlight and warmth than the other for half the year. Twice a year, earth’s tilted axis and its orbit around the sun come together just so that the amount of light and dark are equal around the globe. Hereafter our time in the sun will grow shorter each day as the sun creeps ever southward of due east until reaching winter solstice in late December, its farthest point south in our skies.

A pair of planetary pairings

The waning moon rises in the late evening at week’s end and is high in the southwest with the approach of the rising sun. Each night it rises a half-hour later, so that by last-quarter on the 15th it crests the northeast horizon at midnight.
    The moon Saturday night and Sunday before dawn shines a few degrees below the smallest of the three celestial dippers: the Pleiades star cluster. This grouping of stars marks the shoulder of Taurus the bull and is a few degrees to the northwest of Aldebaran, the bull’s red eye. Aldebaran marks one end of another star cluster within Taurus, the Hyades, which is the V-shape of the bull’s face.
    Monday before dawn the moon trails just a few degrees behind Aldebaran. Early morning Tuesday the moon shines less than 10 degrees above Betelgeuse, the shoulder of Orion the hunter.
    Far to the east of Orion is Jupiter, which rises around 3:30am and is high overhead as daybreak approaches. By that time you might be able to spot Venus low against the horizon. The Morning Star is exponentially brighter than Jupiter, but so close to the horizon and the approaching sun that you may need binoculars to pick her out of the haze. Aligned halfway from Venus to Jupiter is Regulus, the blue-white heart of Leo the lion.    
    The other two planets visible to the unaided eye, Mars and Saturn, form a line of their own with the star Antares to the southwest in the evening sky. The two planets shine at nearly the same magnitude, but their colors make it easy to tell them apart. Not so with Antares, whose name literally translates to Rival of Mars. The red heart of Scorpius is farther to the east and is not as bright as the red planet. In the coming days Saturn sinks ever closer to the horizon, while Mars gains ground moving to the east. By month’s end Mars will be just a few degrees from Antares.
    Summer may be on the wane, but the season’s stars still command the evening sky. As the sun sets, look directly overhead for the zero-magnitude star Vega in the constellation Lyra. By 10pm first-magnitude Deneb, the head of Cygnus the swan, has taken the perch atop the celestial zenith. South of Vega and Deneb is Altair, the eye of the eagle Aquila, and the third point in the Summer Triangle.

Close as Mercury, far as Neptune

The moon waxes through our evening skies from a thin crescent at week’s end to first-quarter Tuesday September 2. Friday Luna shines just two degrees above the first-magnitude star Spica low in the southwest.
    Sunday the moon appears farther east at sunset, forming a tight triangle with Saturn to the west and Mars to the south. The two planets appear equally bright, shining at magnitude 0.6, but Saturn’s golden glow and Mars’ red hue make them easy to tell apart.
    Monday evening the moon shines at the head of Scorpius, which is marked by three slightly mis-aligned stars. The moon is just one degree above the northernmost of the three, Graffias, shining at magnitude 2.5. Ten degrees southeast of the moon is the red giant Antares, the heart of the scorpion.
    As the sun dips beneath the horizon around 7:40, look in its wake for Mercury low in the west. Binoculars may help you pinpoint this elusive planet. When most people spot Mercury, they are surprised by its brightness, shining around zero magnitude, brighter than most stars. But the innermost planet orbits so close to the sun that it never appears more than a dozen degrees above the horizon during dark hours.
    Mercury has been a fixture of our night sky since the dawn of civilization. The first telescopic observations of the planet were made by Galileo in 1610, but unlike his viewing of Saturn, there was no eureka moment. It was not until more than 350 years later with the fly-by of the Mariner 10 space probe that astronomers learned much more about this elusive planet.
    You may be able to see the farthest planet from the sun, Neptune, before dawn this week. On Friday the outermost planet reaches opposition, when earth is directly between it and the sun. Even with binoculars or a small telescope it will appear as little more than a small blue dot low in the west-southwest amid the dim stars of Aquarius.
    Venus and Jupiter will greet you in the east before dawn amid the glow of the coming sun.

Escape urban lights to see this sight

     Each August, as the kids head back to school, the galaxy is tilted  in such a way that the Milky Way stretches overhead in full glory. With Monday’s new moon, this may be the best week of summer to gaze on this river of stars. To fully appreciate it you’ll need dark skies away from any urban glow well after sunset. Give your eyes a few minutes to get accustomed to the darkness, tilt your head back and get lost in the glow.
    From Perseus and Cassiopeia in the north-northeast, the Milky Way flows down through Cygnus the swan onto Aquila the eagle. From the eagle’s tail, the glow of stars splits, one section continuing to Sagittarius, the other to Scorpius in the southwest; the dark space in between is called the Great Rift. But this patch of the heavens is not bereft of stars. Our view of them is blocked by masses of interstellar gas and dust. Of course it isn’t just the flowing river of stars that make up the Milky Way but almost every star we see with the unaided eye, including our own sun. All are part of the same spiral galaxy. Our solar system is at the end of one of the spiral’s arms. When we look at the river of stars, we are looking toward the center of the galaxy, through layers of light that combined form the glowing band that we see on a beautiful dark night.
    As evening twilight gives way to darkness, Mars and Saturn appear in the southwest. Mars has been inching toward the ringed planet night by night and will pass below it over the weekend, coming within three degrees. The two planets appear equally bright, but you should have no trouble telling Mars’ reddish hue from Saturn’s golden glow. While you’re comparing colors, look a few degrees to the north of the two planets for the star Zubeneschimali in the constellation Libra. This is the only star with a greenish glow visible to the unaided eye — at least to some. What about you?
    Venus and Jupiter rise in the east-northeast before dawn. Jupiter is first to crest the horizon, but once Venus appears a few minutes later you’ll have no trouble telling the two apart, as the morning star is six times brighter than old Jove. The two planets are joined by the ever-so-thin waning crescent moon early Saturday morning.
    The last of the naked-eye planets returns to view late this week. Look for Mercury Wednesday the 27th immediately in the wake of the setting sun and just a couple degrees from newly emerged waxing crescent moon.

The sun stands still for just a day before again heading south

In the early morning Saturday, at 6:51am EDT, the sun reaches its northernmost point in the sky for the year, with its center hovering directly above the Tropic of Cancer somewhere in Africa. On solstice, the sun appears to pause in place, holding steady for several days directly overhead at high noon — solstice in fact means sun standing still. You can see proof of the sun standing still in this week’s times of sunrise and sunset, listed below, which barely change.
    This solstice marks the Northern Hemisphere’s longest day of the year, with 14 hours 54 minutes of sunlight here along Chesapeake Bay. And while there is no universal body that dictates the start of the seasons, this celestial phenomenon is universally seen as the start of summer for the Northern Hemisphere and the start of winter for those below the equator.
    The earth spins at a 231⁄2-degree tilt, causing the north side of the planet to more directly face the sun for half the year and the south side to more directly face the sun the other half of the year. At the time of the June solstice, the North Pole points almost directly at the sun, while December’s solstice has the South Pole pointing sunward. Right now, we’re enjoying that sunward tilt, and all those extra hours of daylight add up to the season’s much warmer temperatures.
    While it is only the start of summer and the days will continue to grow warmer for some time to come, it is also the beginning of summer’s end. The very next day after solstice, the sun begins its southward march, albeit ever so slightly at first, and the length of daylight wanes.
    For millenia, cultures have tracked the sun’s path across the sky, measuring the length of daylight and the location of the sunrise and sunset throughout the year. The ancient Celts built Stonehenge, built at least 5,000 years ago in alignment with the solstices and sunrise. Around the same time, the Egyptians were building their own monuments to the sun and the passing seasons. From a vantage atop the Great Sphinx on the day of June’s solstice, the sun set directly between the oldest of the Great Pyramids.
    The sun may be the star this week, but the waning crescent moon makes good showings with Venus low in the east before dawn Monday and Tuesday, when only two degrees separate the two. Early Wednesday the moon is just above of the bright star Aldebaran in Taurus.

Mars still lights up the night
Thursday’s first-quarter moon appears high in the southwest at sunset and sets in the west around 1am. Each following night, darkness finds the waxing gibbous moon a dozen degrees farther east, providing almost an hour of additional moonlight. 
 
Friday, the moon is 15 degrees to the right of Mars, but come Saturday the two are practically on top of one another, separated by only two degrees. The red planet is just to the upper right of the moon as darkness falls, and they stay quite tight until setting around 2am. At -0.8 magnitude, Mars outshines any star — only Sirius is brighter, and the Dog Star is gone from view for the season. 
 
Two months ago Mars was even brighter, as the planet was at opposition from the sun with earth directly between the two. Imagine opposition as if you were seated at the movie theater, the light from the projector streaming from behind you to the screen. The screen itself isn’t illuminated, but instead it reflects the projected light back to your eyes. As you turn your gaze from straight ahead, or if you shifted the projector, the reflected image grows dimmer. That’s what’s happening now, as earth’s faster orbit hustles it away from Mars, diminishing the angle of reflected light.
 
To see a simulation of the intricate dance between earth and Mars as they travel around the sun, go to http://tinyurl.com/9dtvspa.

Sunday the moon has another partner, the first-magnitude star Spica. The brightest star in the constellation Virgo, Spica is just a couple degrees to the moon’s right. A dozen degrees to the west of the pair is Mars, while a dozen degrees to their east is Saturn.
 
Monday the moon shines 10 degrees to the right of Saturn, while Tuesday it is five degrees to the left of the ringed planet.
 
As the sun sets Wednesday, the moon appears low in the southeast. Just a few degrees below the nearly full moon is the first-magnitude red-giant Antares, the heart of Scorpius the scorpion. Antares means literally the opposite, or rival, of Mars, because of its own reddish hue. Compare the two for yourself.

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.