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Articles by J. Alex Knoll

Halloween falls right in between

The waxing moon reaches first-quarter Thursday, and as darkness falls on Halloween, it shines high in the south, with the bright star Fomalhaut almost straight below.
    As a holiday, Halloween stretches back thousands of years, but not as a day of costumes and trick-or-treating. It coincides with earth’s path around the sun, falling midway between autumnal equinox and winter solstice.
    The Celts of pre-Christan Britain called this cross-quarter day Samhain, celebrating both the end of the harvest and the end of the year. On this night, the veil between the world of the living and the realm of the dead was thought to be especially thin, so people lit bonfires and lanterns from hollowed-out gourds to ward off spirits.
    As Christianity spread, it merged its own holy days with the pagans’ cross-quarter holidays. Imbolc became Candlemas, now better known as Groundhog Day; Beltane gave way to May Day; Lugnasad became Lammas. And Samhain was absorbed into All Saints Day or Hallowmas, marked on November 1, with the night before Hallow’s Eve.
    Now the cross-quarter day coincides with another ritual, setting our clocks back an hour in the return to Standard Time at 2am the first Sunday of November.
    The first week of November provides the best view of Mercury before dawn. The innermost planet reaches greatest elongation November 1, its farthest west of the sun and its highest in our sky. An hour before sunrise, look for it not quite 10 degrees above the east-southeast horizon — roughly the size of your fist at arm’s length. At magnitude –0.6, Mercury is brighter than any nearby star (all but Sirius, in fact), but binoculars may help locate it in the glow of twilight. Don’t confuse the bright planet for Arcturus higher in the east-northeast.
    You shouldn’t have any trouble finding Jupiter. The gaseous giant rises around midnight, and as dawn approaches it is high in the southeast, bluish Regulus and the other stars of Leo the lion stretched out below it.
    Mars is the only planet visible in the evening, shining no brighter than your average star but still a distinct orange-red. Look for it low in the southwest as darkness settles, where it will remain the rest of the year.
    Early November marks the peak of the South Taurid meteor shower. The higher the constellation Taurus, the more meteors you’re likely to see, although the waxing moon will limit you. Still, the Taurids can deliver the occasional fireball.

Even eclipsed, this star blinds

If you didn’t already know about the partial solar eclipse just before sunset Thursday, you’re not likely to have solar glasses at the ready. Do not look at the eclipsed sun for even a moment as it can cause lasting eye damage or blindness. But you can still watch safely with little preparation.
    Try projecting the image through binoculars. Cover one lens and aim the other at the sun, pointing the eyepiece toward the floor or a piece of paper until the sun’s orb appears. Bring it into focus, and voila! You may want to use a tripod, and you can use a small telescope in the same fashion.
    Another option for watching the sun is a pinhole projector, a perennial science project requiring only two sheets of white paper and a pin. Poke a clean round hole in a sheet of paper. With your back to the sun, hold the pierced paper between the sun and the second sheet of paper until you see the sun’s inverted image projected onto it. Increasing the distance between the two sheets enlarges the image but decreases its sharpness. Or you can get more elaborate using the same principles with a box large enough to put over your head to create a viewing chamber.
    Here along Chesapeake Bay, the eclipse begins Thursday at 5pm with the sun low in the west. Alas, it will still be in full swing come sunset at 6:17pm.
    The eclipse won’t be your only chance to put a pinhole projector to use. The sun right now is in the midst of a massive solar storm, resulting in sunspots large enough to see with the protected-but-unaided eye.
    Sunspots start as massive magnetic bursts deep within the sun that migrate to its surface. While highly charged, this energy is cooler than the sun itself, thus appearing darker than surrounding areas. Once to the surface, the energy flares into space in what are called Coronal Mass Ejections, which can wreak havoc on satellites and take down sections of the power grid. Already the International Space Station has turned to face away from the sun to limit the damage from this solar storm.
    Out of all this violence comes beauty, too, in the form of the Northern Lights. So keep a lookout, as a solar storm of this magnitude could make them visible this far south. Learn more at SpaceWeather.com.
    The moon returns to view Saturday as a thin crescent very low in the west-southwest. Look to its lower right for Saturn. As the moon waxes into the new week, it shines near the planet Mars.

It’s a crowded solar system

If you’ve been out before dawn you’ve likely seen Jupiter blazing in the east. Early Friday morning, the gaseous giant shines left of the waning crescent moon. The following morning you’ll find it above the moon and forming a loose triangle with the star Regulus, the heart of Leo the lion.
    The only other naked-eye planets visible are Mars and Saturn, low in the western sky in the darkening twilight. Saturn is fast on the heels of the setting sun, while Mars is farther to the east. Don’t confuse Mars for Antares, the red heart of Scorpius and roughly midway between the two planets.
    Mars has a close encounter Sunday, when Comet Siding Spring (C/2013 A1) passes within 82,000 miles of the red planet. For comparison, the moon orbits the earth by almost 240,000 miles, and the closest recorded comet to pass us was in 1770 at 1.4 million miles! While a collision isn’t predicted, the comet’s tail will likely engulf the red planet. Even with binoculars you’ll be hard-pressed to see Comet Siding Spring, but a telescope will reveal it above the red planet.
    We have our own close encounter with a comet — Halley’s Comet, no less — in the form of the annual Orionid meteor shower, which peaks late Tuesday and early Wednesday. The comet hasn’t visited the inner solar system since 1986, but each year at this time earth passes through the trail of debris left behind from its countless orbits around the sun. With the waning crescent moon rising shortly before dawn, you might see from 20 to 25 meteors an hour. They can appear anywhere in the sky, but if you trace back their path they radiate from the constellation Orion.
    The sun and moon have a close encounter of sorts Thursday the 23rd, resulting in a partial solar eclipse in the early evening. Be warned: Gazing upon a solar eclipse can cause blindness, and a partial eclipse is all the more dangerous, so look only with a solar filter.
    Just as it takes a full moon for a lunar eclipse like the one two weeks ago, a solar eclipse coincides with new moon, when it passes between sun and earth, blotting out the sun’s disc — or part of it in the case of this partial eclipse.
    Hereabouts the show begins at 5:52pm, with the greatest point of eclipse coming at 6:08, when one-third of the sun is blocked from view. Alas, the sun sets at 6:17 before the eclipse is over.
    Again, do not attempt to watch the eclipse without protective eyewear; use the coming week to find solar glasses or another proper filter.

Its far side is always dark to us

The dark hours at week’s end are still brightened by the glow of the waning Hunter’s Moon, which rises mid-evening and dominates the night sky until daybreak. On clear days this week, you may even see the moon in the west after sunrise.
    Over the weekend, the moon travels with the constellation Taurus. Friday it is 10 degrees to the right of the Pleiades star cluster while the bull’s red eye Aldebaran is a little farther below the moon. The brightests stars of the Pleiades form a small but distinct dipper, which makes up the bull’s back. Saturday the moon is much closer to Aldebaran and the Hyades star cluster, which makes up the bull’s face. If the moonlight is too much to discern these stars, wait a day or two until the waning moon has shifted to the west.
    Just like here on earth, half the moon is always illuminated by the sun and the other half facing away from the sun. But as the angle between the sun, earth and moon changes, so does the portion of the moon’s illuminated face that we can see. With the moon waning, the angle is closing, obscuring more of the lunar surface behind earth’s shadow. This darkened section of the moon still faces earth and should not be confused with the so-called dark side of the moon. Better to think of that as the far side of the moon, which faces away from earth. The far side is still bathed in sunlight — we are just never in a position to witness it.
    The moon rotates on its own axis, with one side facing the sun for about two weeks and then facing away from the sun the next two weeks. Over billions of years, earth’s stronger gravitational pull has slowed the moon’s rotation to the point that it spins in synch with its pace around the earth. As a result, one side of the moon faces earth only during new phase, when it is between us and the sun, obscured by the light of day. So we never see the far side of the moon.
    Mars and Saturn pop into view in the wake of the setting sun. Saturn is sinking fast and is visible for less than an hour. Mars is well to the east of Saturn but not quite as bright. Don’t confuse it for the similarly hued star Antares, the heart of the Scorpion wriggling below.
    Jupiter rises around 2am and is high overhead in the east as morning approaches. Over the next month this gaseous giant climbs higher and grows brighter in our pre-dawn sky.

Earth’s shadow blots out this week’s full moon

With sunrise now after 7am, perhaps you’ve seen an exceptionally bright light in the south before dawn? Looking up, did you see the constellation Orion? That’s Sirius, the brightest star in the heavens, known as the Dog Star for its place amid Canis Major. Sirius rises around 2am in the east-southeast. Close to the horizon, it pulses a dazzling rainbow of colors, its light refracted by earth’s atmosphere like that from a prism. Closer to daybreak, when Sirius is high in the south, its light cuts through less of our atmosphere and appears a brilliant, cold white. As if Sirius didn’t stand out from its brightness alone, the three belt stars of Orion point straight down to the Dog Star.
    Perhaps, though, you’re looking due east in the hour before sunrise. In that case you’re seeing Jupiter, which outshines even Sirius. The giant planet rises around 3am, and by 6am it is high in the east. Below Jupiter is the constellation Leo with its upper body looking like an inversed question mark with Regulus at the bottom.
    You’ll want to get up before dawn Wednesday to catch the total lunar eclipse of the full, Hunter’s Moon. An eclipse of the moon only occurs during full moon, when it is aligned just so with the earth and sun, which casts earth’s shadow over the lunar surface. The process begins after 4am as the moon grows darker under the outer, penumbral, shadow. A little after 5am, the full, umbral, shadow begins to take a growing bite from the moon’s left edge until it is completely over-shadowed by 6:30. Mid-eclipse is at 6:54, after which point the rising sun breaks the spell.
    At the other side of darkness, Mars and Saturn appear at sunset. Saturn is fast on the heels of the sun, low in the southwest at dusk. Night by night the ringed planet is sinking lower and inching closer to the sun until it disappears around month’s end. Mars trails Saturn by roughly 20 degrees. Normally its red hue makes it easy to spot, but you may think you’re seeing double, as Mars is less than five degrees above another red light, Antares, the heart of Scorpius, whose name means rival of Mars. Over the coming weeks Mars creeps higher while the scorpion sets from view for winter.

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.