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Articles by J. Alex Knoll

No need for fireworks here

While you’re waiting for fireworks in the gathering darkness, impress your friends and family with a quick orientation of the celestial lights popping into view.
    First to emerge in twilight’s glare is Venus, low in the west, so bright you might confuse its twinkling with a jet high overhead. With a little more darkness, Jupiter pops into view a little to the right of Venus. To the upper left of the two planets is Regulus, the heart of Leo the lion. The three provide a good contrast in brightness, with Venus blazing at –4.6 magnitude, Jupiter outshining any star at –1.8 magnitude, and Regulus still quite prominent at 1.6 magnitude.
    The month began with Venus and Jupiter less than one degree apart, and on July 4th they are still within two degrees of one another. But they are parting ways, with Venus moving closer to Regulus and Jupiter inching to the northwest and the wake of the setting sun.
    By 9pm, Arcturus, the brightest star of summer is directly overhead. Shining at magnitude –0.1, it is the lead star in the constellation Boötes the herdsman, who tends the bears Ursa Major and Ursa Minor, which contain the Big and Little Dipper respectively.
    To the east of Boötes is the Hercules, most notable for its trapezoid-shaped keystone. Look for the minor constellation Corona Borealis, the Northern Crown, between Boötes and Hercules.
    To the east of Hercules are the three constellations that host the Summer Triangle. The smallest constellation, Lyra, hosts the brightest star, zero-magnitude Vega. From there look for first-magnitude Deneb at the head of the Northern Cross, Cygnus the swan. The final point in the triangle is Altair, the eye of the eagle Aquilla, shining at magnitude 0.8.
    Low in the south-southeast at sunset is golden Saturn at the head of Scorpius. The heart of the scorpion, Antares, shines a dozen degrees to Saturn’s lower left of Saturn twinkles fiery orange Antares, not quite as bright.
    Early risers can spot Mercury above the east-northeast horizon about 40 minutes before sunrise. Binoculars will help pick it out of the growing glow of dawn. Don’t confuse it for Aldebaran, the eye of Taurus the bull, much higher overhead.

Earth’s 23.5-degree axis gives us summer, winter and everything between

As evening twilight settles Thursday, look to the western horizon for the nascent crescent moon. Above it are Venus and Jupiter. The bright star Regulus is up there, too, forming a line with Venus and Jupiter, each roughly a dozen degrees from the next. Keep an eye on the two planets as they inch closer together over the next two weeks before a spectacular end-of-month conjunction when they are within one-third degree of one another.
    Friday and Saturday the moon, Venus and Jupiter form a loose triangle. By Sunday the moon is far to the left of the planets but is just a few degrees below Regulus and the Sickle of Leo. The Sickle, which looks like an inverted question mark, outlines the head of the lion.
    While Venus and Jupiter glimmer above the western horizon, Saturn shines off to the east. By midnight it is at its highest almost due south. Don’t confuse its steady golden glow for the brighter red star Antares, which is a dozen degrees below. With greater magnification there’s no confusion: Saturn’s rings appear as a distinct bulge with even binoculars, and seen through even a modest telescope the rings themselves come into view.
    You’ll need binoculars to spot Mercury, which is emerging from the sun’s glare before dawn low in the east-northeast. Early Wednesday morning provides the best view of Mercury as it reaches its greatest eastern elongation, its point farthest from the sun in our sky, when it will peak 22 degrees above the horizon and remain visible 45 minutes before obscured by daybreak. Mercury is bright, but a couple degrees below it the star Aldebaran shines brighter still.
    Sunday at 12:38pm marks the summer solstice, when the sun reaches its northernmost position in the sky. ­Because the earth spins at an odd, 231⁄2-degree angle as it orbits the sun, the Northern Hemisphere is currently positioned to receive far more sunlight than the Southern Hemisphere. On the summer solstice, the sun appears to stand still above the Tropic of Cancer, which straddles the earth 231⁄2 degrees north of the equator. After the solstice, the sun will slowly shift southward from day to day until six months from now it is at its southernmost extreme over the Tropic of Capricorn, which is 231⁄2 degrees south of the equator. The sun shifting from one extreme to the other is what causes our seasons here on earth. Were the planet to spin upright like a top instead of tilted, the seasons would never change, with perpetual summer along the equatorial band and growing ever darker and colder the farther north or south you went.

The sun follows its own clock

As darkness falls, first Venus then Jupiter pop into view in the wake of the setting sun. Venus blazes at magnitude –4.4, exponentially brighter than Jupiter at magnitude –2, which still outshines any star. The two planets are inching closer on their way to an end-of-month rendezvous. This week the gap between the two shrinks to 10 degrees — close enough to obscure both with your fist held at arm’s length.
    Keep an eye on Venus this weekend. It is near the center of the dim Y-shaped constellation Cancer, which in itself is not that interesting, boasting no star brighter than 3.5 magnitude. In fact, were it not placed on the ecliptic, the path of the sun, moon and planets as they circle overhead, Cancer would be a minor constellation, certainly not a denizen of the zodiac or even an astrological sign. Cancer’s claim to fame is no star but what appears as a faint, fuzzy patch of light to the unaided eye, M44, the Beehive Cluster.
    Viewed with binoculars, however, the Beehive comes to life with dozens of stars, and with a telescope it swarms with hundreds of stars. Friday and Saturday Venus is less than one degree from the Beehive in the western sky at nightfall and visible for at least an hour after sunset.
    Friday marks our earliest sunrise of the year, almost 10 days before the solstice. The discrepancy is the result of several factors, but in short, our clocks keep different time than the sun. While the clock measures a day with the passing of each 24 hours, a solar day is measured from the time of one high noon to the next. Hereabouts on the 12th, that is 24 hours and 15 seconds. Prior to the solstice this temporal slack is made up for at dawn, while after solstice the difference is at sunset. So while the summer solstice is June 21, our earliest sunrise is always some 10 days before, and the latest sunset another 10 days after solstice. In winter, the same phenomenon is at play, only reversed, and more pronounced, with nearly two weeks between earliest sunset and solstice and solstice and latest sunrise.

Seach the sky for Berenice’s hair and Ariadne’s crown

The moon wanes to last-quarter Tuesday, rising more than a half-hour later each night, providing an increasingly darker backdrop for sky-watching.
    As the evening sky begins to darken, the first lights to appear are the planets Venus and Jupiter high in the west. Then you might notice golden Saturn aglow in the southeast. The next brightest object to appear is Arcturus, almost directly overhead.
    Arcturus is the third brightest star in the heavens and is the lead star in the constellation Boötes. It is a red giant 36 light years away burning more than 100 times brighter than our sun. Its name is derived from the Greek word Arktouros, meaning guardian of the bear. Boötes follows Ursa Major along the ecliptic, while behind it is the constellation Hercules. Closer to either side of Arcturus, however, are two lesser-known constellations.
    To the east of Boötes shines a semi-circle of severn stars, Corona Borealis, the northern crown. By about 11pm, this constellation is almost directly overhead. In Greek mythology, this is the crown Dionysus gave to his bride Ariadne. Celebrating after their wedding, Dionysus threw the crown into the sky, where the jewels turned into stars and the crown became a constellation. The lead star in Corona Borealis is Gemma, almost as bright as the North Star.
    To the west of Arcturus is Coma Berenices, or Berenice’s Hair, most notable by three not-so-bright stars making a 90-degree angle. The legend of this constellation dates back to Queen Berenice II of Egypt, whose husband Ptolemy III Euergetes was away in battle. Praying to the goddess Aphrodite, Berenice swore to cut off her long, blonde hair if Ptolemy survived. Upon his return, the queen kept her word and placed her locks on an altar in Aphrodite’s temple. The next morning the hair was gone: the goddess of love was was so pleased with Berenice’s beautiful hair that she placed it forever in the heavens.
    Venus is at its best this week, ­Saturday reaching greatest eastern elongation — or in layman’s terms, its farthest from the sun, 45 degrees as seen from our earthbound vantage, and thus at its highest point in our sky. As the sun sets, look for the Evening Star high in the west. Hereafter, Venus ever so slowly inches toward the setting sun. By mid-August, Venus disappears behind the sun, reappearing in the pre-dawn sky a couple weeks later.
    Jupiter shines a dozen degrees to the upper left of Venus. The two planets are closing in on each other on the way to a close conjunction at the end of the month.
    Sunset reveals Saturn in the southeast, and by midnight it is high in the south. Even a modest telescope will reveal the planet’s famous rings, which are right now tilted at their best angle for viewing. Roughly 10 degrees below Saturn is orange Antares, the lead star in the constellation Scorpius.

Our atmosphere tints summer moons

The moon waxes through the weekend, reaching full phase Tuesday, June 2. This time of year the moon follows a low, lazy arc above the southern horizon. At such a low angle to the horizon, before reaching our eyes the moon’s light must cut through much more of earth’s atmosphere than in winter, when the moon shines high overhead. Gases and trapped moisture within the atmosphere combine to tint the image we see a red, orange or yellow, which explains the names of June’s full moon: the Strawberry Moon, the Rose Moon and the Honey Moon.
    Friday night, the moon is joined by Spica, the blue-white first-magnitude star of Virgo, which is just a few degrees below and to the right of the moon.
    Saturday the moon has pulled westward and is midway between Spica to its right and Saturn to its left. Sunday the moon is less than 10 degrees to the left of Saturn, and Monday it is just two degrees to the the left of Saturn with red-orange Antares a few degrees below.
    Having just reached opposition, its closest point to earth and dead-opposite the sun, Saturn rises as the sun sets, is high overhead at midnight and sets with daybreak. Shining at zero magnitude, Saturn is brighter than it’s been in eight years. Better yet, its rings are positioned to allow the best possible viewing and appear all the brighter so close to opposition.
    Saturn isn’t the only planet visible after dark. Sunset reveals Venus high in the west and Jupiter 20 degrees higher still. Night to night, Venus is gaining ground on Jupiter leading to a grand conjunction in late June. Monday Venus forms a near-stright line with the Gemini twins Pollux and Castor.
    By late-evening the stars of the Summer Triangle are perched above the east horizon. Farthest west is the brightest and the fifth-brightest star, Vega, of the constellation Lyra. Off to the southeast of Vega and almost as bright is Altair of Aquila the eagle. Closing the triangle is first-magnitude Deneb, the head of Cygnus the swan.

After almost 4,000 days in space, this probe died for science

This week Mercury shows its best face in homage to the Messenger spacecraft, which crashed into the planet early morning April 30.
    The craft was launched in August 2004 and reached Mercury in March 2011, the first to orbit the innermost planet. Since then it has circled Mercury more than 4,100 times, compiling more data in the process than everything combined before that.
    Thursday, April 30, scientists at Johns Hopkins Applied Physics Lab cut life support on their prodigy, and shortly thereafter the craft fell from orbit, plummeting to the surface at more than 8,750 miles an hour. Messenger was already running on borrowed time, having exhausted its traditional fuel supply, but programmers were able to supplement it with helium onboard for other reasons. Now that, too, is exhausted.
    “I guess the end is coming,” the Messenger team posted earlier on Twitter “After 10 years, spacecraft will end life as just another crater on Mercury's surface.” A big crater, more than 50 feet wide.
    The elusive planet is not only difficult to spot, it had been difficult to study before Messenger. Less than 45 percent of Mercury’s surface had even been photographed, and that decades ago. In its four years in orbit, Messenger sent more than a quarter-million photos back to earth. it found volcanoes, discovered polar caps of frozen water and studied Mercury’s chemical makeup.
    Mercury “is crucial to developing a better understanding of how the planets in our solar system formed and evolved,” NASA explains on its Messenger website. “Mercury is an extreme: the smallest, the densest, it has the oldest surface, the largest daily variations in surface temperature — and it’s the least explored.”
    Mercury reaches its greatest elongation from the sun on May 7, climbing 20 degrees above the horizon. Look for it low in the west just after sunset this week. You may need binoculars close to sunset when it’s at its highest, but by 9pm it should easily be visible as it prepares to set. Much-brighter Venus is 20 degrees higher, and Aldebaran, the red eye of Taurus the bull is 10 degrees to Mercury’s left.
    These are the last nights to see Mars, which is even deeper in the glare of sunset than Mercury. Jupiter shines high in the south at nightfall, while Saturn rises around the same time. Look for the just-past-full moon near Saturn Monday and Tuesday night.

The moon visits the Beehive Cluster and more

The waxing moon reaches first-quarter phase Saturday, shining below and to the left of Jupiter. The moon is near the center of the constellation Cancer.
    Were the crab not on the ecliptic, it’s doubtful it would hold its place in the zodiac, as none of its stars are brighter than 3rd magnitude. (The ecliptic is the path of the sun, moon and planets as they circle through our skies.) But what it lacks in bright stars it makes up for in sheer quantity, as it hosts the Beehive Cluster. The Beehive is near the center of Cancer, about halfway between Regulus in Leo and Pollux in Gemini. Seen with the unaided eye, it appears as a dull smudge of light. However, binoculars or a small telescope reveal dozens of individual stars. But there’s even more to the Beehive than that, as it is a stellar incubator with thousands of infant stars.
    With binoculars at hand late Saturday and early Sunday, see if you can spot the ninth-magnitude asteroid Juno just above the moon. Your best chance is around 2am when the moon is about to set and the two appear above the west-northwest horizon.
    Sunday the moon is to the lower left of Jupiter, while above and to the left of the moon is the first-magnitude star Regulus, the three forming a near-perfect triangle. By Monday the moon lies just four degrees below Regulus.
    The five naked-eye planets are visible this week. Venus blazes in the west in evening twilight and sets in the west-northwest nearly two hours after dark. Scour the horizon below Venus for Mercury, appearing 30 minutes after sunset. The innermost planet is surprisingly bright, unlike Mars, which is just a few degrees to Mercury’s upper left. Jupiter shines high in the south as darkness falls and sets a little after 2am. Saturn rises with Scorpius around 10pm and is high in the south come dawn.

Equinox divides not only day and night but the seasons, too

The new moon winks from sight Friday, obscuring the sun in a total eclipse as seen in a narrow strip over northern oceans. Only residents of a few scattered islands between northern Great Britain and Greenland will see the full eclipse, but viewers across Europe and parts of Asia and Africa will see a partial eclipse.
    The nascent crescent moon returns just after sunset Saturday low against the western horizon. Look just above the crescent’s right tip for Mars, so faint you might need binoculars to see it. In contrast, Venus blazes a dozen degrees above the moon and puny Mars.
    The moon is much easier to spot Sunday evening, now to the left of Venus. About a fist-width to the upper right of the Evening Star, look for the second-magnitude star Hamal, the brightest in the minimalist constellation Aries.
    Monday, the waxing crescent moon shines well above Venus and below the Pleiades star cluster. Venus is so bright you can see it before the sun sets, but you’ll need full darkness to see the stars of the Pleiades, which make up the shoulder of the constellation Taurus. With the unaided eye, most people can see only six of the Pleiades, also known as the Seven Sisters. With binoculars, however, there are far more stars than sisters. The Pleiades is an interstellar incubator of gas and dust with thousands of stars dating back 100 million years. A mere 430 light-years from earth, the Pleiades is one of the nearest star clusters.
    Tuesday, the moon passes close to Aldebaran, the red eye of Taurus the bull, and the constellation’s other star cluster, the V-shaped Hyades. In Greek myth, these were nine sisters, daughters to Atlas and half-sisters to the Pleiades, which are off to the right. The Hyades mark the face of the bull.
    Friday’s vernal equinox ushers in spring for us in the Northern Hemisphere. At 6:45pm EDT, the sun hovers directly above the equator. High above the equator extending into space is another equally imaginary line, the celestial equator, which divides the heavens into a northern and a southern hemisphere. For the past six months, the sun has been in the southern celestial hemisphere, robbing us of more daylight the farther south it dips.
    Since winter solstice the sun has inched away from its southern nadir, and our days have grown longer. On the vernal equinox, the day is divided more or less equally between light and darkness.
    For the next three months, the sun climbs higher and higher into the northern celestial hemisphere before reaching its northern apex above the Tropic of Cancer on the day of summer solstice. Then it spends another three months slowly dipping southward to the second point of balance, the autumnal equinox.

Here on earth and in the skies, the seasons are changing fast

While our bodies are getting used to the hour shift brought about by Daylight Saving Time, Mother Nature is working fast to counter our dark mornings, and within a month day break will come at the same time it did before we switched our clocks.
    At no other point in the year do the days grow longer at a faster pace, as we gain more than three minutes of sunlight each day here in the Northern Hemisphere. Since solstice, December 21, we have gained more than an hour of sunlight in both the morning and at day’s end.
    These days of fast-growing light were called The Quickening by the ancient Celts. 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 once-frozen soil. All around us, the earth’s pulse is picking up its pace.
    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. Six months of the year the constellation is absent and the land falls into stasis as the goddess mourns her daughter Persephone’s confinement in the underworld with husband Hades. Now, with Persephone’s return, the mother’s grief ends and the land again begins to bloom.
    Next to rise is Boötes, the herdsman of the two bears, Ursa Major and Ursa Minor. In Greek legend, Boötes is Arcas, son of the nymph Callisto and Zeus and the first to harness a team of oxen to the plow, revolutionizing farming and ushering in the era of agriculture. Each year, Boötes returns to our evening skies to usher in the spring planting season.
    The scorpion Scorpius crawls over the eastern horizon as winter’s great hunter Orion sets in the west. In Greek myth, Orion had both jilted the goddess Artemis and boasted that he was the superior hunter. Enraged, she sent the scorpion to kill him. Look for the two stinger stars, Shaula and Lesath, less than one-half degree apart. Called the Swimming Ducks, this pair returns to morning skies to signal the coming of spring. From the Arabic Al Shaulah, the sting, Shaula is the 24th-brightest star in the sky, although it often goes unnoticed, as neither duck climbs high above the horizon at our latitude.
    Before dawn of Friday the 13th, the last-quarter moon shines near the head of Scorpius with ringed Saturn close by. The heart of the scorpion, the red-giant Antares, shines less than 10 degrees to the lower left of Saturn.
    Venus rules the early evening, perched above the western horizon and blazing at magnitude –4. A few weeks ago Mars appeared within a few degrees of Venus, but now the red planet well below and pulling farther away night by night.
    With sunset, Jupiter appears high in the east, perhaps the first “star” you see in the gathering night. as the stars come out. By 11pm it is nearly overhead, finally setting an hour before sunrise.

There’s work overhead on the ISS

Thursday evening the waxing gibbous moon stands above the constellation Orion, appearing as if it were the hunter’s head in profile. The next night it is above and to the left of Betelgeuese, Orion’s shoulder, and the two form a nice line with Rigel, the hunter’s foot. Saturday Luna is below the twins of Gemini, Castor and Pollux, and above Procyon, the lead star in the constellation Canis Minor, the Little Dog. Off to the east is brilliant Jupiter. Sunday the moon rests in the middle of a triangle formed by Pollux, Procyon and Jupiter. Come Monday, Luna is just five degrees south of Jupiter. Tuesday the moon is to the upper right of Regulus, with Jupiter well above them both. Then on Wednesday, the moon, Jupiter and Regulus form a loose triangle.
    While the moon is our only natural satellite, countless manmade satellites orbit the earth. You’ve likely seen some and presumed they were airliners passing overhead in the night. The International Space Station, however, stands out from the pack, shining brighter than except the sun and moon and zipping across the sky like a shooting star.
    This past week, on February 21 and 25, astronauts aboard the ISS completed two of three scheduled space walks to prepare it for future commercial dockings. The third is planned for Sunday, March 1.
    The ISS was originally designed to receive docking space shuttles, which were secured alongside a berthing port using the station’s robotic arm. Unmanned cargo vessels and Russian Soyuz rockets (the only means of sending and retrieving astronauts to and from the station now that the shuttles have been retired) continue to use this system.
    However, manned commercial vessels, set to begin arrival to the ISS in 2017, will maneuver into a docking port within the station itself — something akin to what we’ve seen in movies and television for decades.
    The current system is a daunting and time-consuming process, both arriving and departing. The new system will allow a quick evacuation of crewmembers from the station in the event of an emergency.
    While we won’t be able to see the ISS during the space walk, it routinely flies overhead. For dates and times, go to http://spotthestation.nasa.gov.