The Sky This Week, June 20 – 27, 2017 !

The Sky This Week, 2017 June 20 – 27

Rites of Summer
Jupiter, with the Great Red Spot
imaged 2017 June 12, 02:24 UT in good seeing from Alexandria, Virginia

The Moon opens the week as a waning crescent in the morning sky, then returns to the evening after New Moon, which occurs on the 23rd at 10:31 pm Eastern Daylight Time. Look for Luna’s slender sliver near Venus on the morning of the 21st. She ends the week tucked up close to the bright star Regulus on the evening of the 27th.

The summer solstice occurs on the 21st at 12:24 am EDT. This event marks the beginning of astronomical summer and is one of the most important dates observed by ancient cultures all around the world. It is on this date that the Sun reaches its most northerly declination and is thus a very easy way to keep track of the annual cycle of the seasons. We can find examples of solstice markers among ancient ruins all across ancient sites in the Northern Hemisphere. Perhaps the most famous of these is Stonehenge, a complex megalithic ruin in southwestern England. This site was the focus of intense activity for over a thousand years, and its earliest development predates the time of the construction of the pyramids of Giza. Its main axis is aligned to the summer solstice sunrise, and there are many other astronomical alignments incorporated in its form. The area surrounding Stonehenge has many other stone and wooden circles, earthen barrows, and long hand-excavated “avenues” that align with the solstice sunrise. In the Americas, solstice alignments are common among the many ancient sites built by ancient cultures like the Maya and Toltecs. In the United States we find such alignments at sites such as Big Horn Medicine Wheel in Wyoming, Chaco Canyon in New Mexico, and Hovenweep National Monument in Colorado. At the time of this year’s solstice the center of the Sun’s disc will touch the Tropic of Cancer just north of Hong Kong on the coast of mainland China. Here in Washington we’ll experience the longest duration of daily sunlight for the year, with Old Sol above our horizon for 14 hours and 54 minutes. Welcome to summer!

If you’re out looking at the stars to welcome the solstice, look to the south during the midnight hour. You’ll see one of the most distinctive constellations in the sky hanging just above the southern horizon. Scorpius is easily recognized by the ruddy star Antares marking the Scorpion’s heart, a vertical row of blue second-magnitude stars to the west of Antares, and a long curving arc of stars dipping down toward the southern horizon. In mythology the lowly scorpion killed the boastful hunter Orion, so the two constellations, each marked by bright reddish stars, were placed at opposite sides of the sky so they would never appear in the sky at the same time.

Jupiter dominates the early evening sky, appearing just west of the meridian after sunset. The giant planet is best seen during twilight and the first hours of astronomical darkness, but he now sets at around 1:30 am so there’s only a limited window to catch a good view of him in the telescope. Watch the moon Callisto pass just north of the planet on the evening of the 20th. On the 23rd, the planet’s famous Great Red Spot, now sporting a prominent orange hue, transits the disc between 9:00 and 11:00 pm.

Saturn wallows in the southern sky throughout the night. The ringed planet crosses the meridian at around 12:30 am, but he never gets higher than 30 degrees above the horizon. Haze and humidity will hinder your view of the planet’s fainter moons, but you should still have a fine view of the wide-open rings in moments of steady air.

You’ll find Venus climbing up from the eastern horizon in the gathering morning twilight. She is very prominent by 5:00 am, and will continue to greet you from this relative position for the next several months. Look for the slim waning crescent Moon nearby on the morning of the 21st.

The Sky This Week, June 13 – 20, 2017 !

The Sky This Week, 2017 June 13 – 20

The last week of spring?
Jupiter with Three Moons
Imaged 2017 June 11, 02:01 UT in good seeing from Alexandria, Virginia

The Moon spends the week crossing the faint constellations of the autumn sky during the early morning hours. She wanes through the Last Quarter phase, which occurs on the 16th at 3:26 pm Eastern Daylight Time. You’ll have to wait until the end of the week before Luna encounters any bright objects. You’ll find her near dazzling Venus on the mornings of the 20th and 21st.

The June campaign for the Globe at Night citizen-science observing program opens its June “window” on the 16th and continues for the following 10 nights. This program is a great way to not only learn to recognize constellations, it also benefits our understanding of how artificial night lighting is spreading around the world. This month’s featured constellation is Hercules, which occupies a sizeable patch of the sky between the bright stars Arcturus and Vega. Although it is a large star pattern, most of its stars are second- and third-magnitude. The center of the constellation is made up of a trapezoid of stars known as The Keystone which forms its most prominent feature. The entire constellation is best seen from darker skies, so it’s ideal for viewing from favorite vacation spots at the shore or the mountains. Visit the Globe at Night website for finder charts and to report your findings. You’ll join nearly 10,000 others who have already reported their observations so far this year.

The summer solstice will occur on the 21st at 12:24 am EDT, but this week we see the earliest sunrises for the year in mid-northern latitudes. Here in the Washington, DC area Old Sol crests the horizon at 5:42 am EDT for the next several mornings before reversing the trend beginning on the morning of the 17th. These early sunrises are offset by the occurrence of later sunsets, which reach their latest for the year on June 24th. This makes June 20th and 21st the year’s longest days, with the Sun above the horizon for 14 hours and 54 minutes. Throwing in the times of astronomical twilight, skywatchers only have just over four hours of total darkness to enjoy completely dark skies.

Take advantage of those dark skies and get away from the city’s heat and smog to enjoy the rising summer Milky Way during the short hours of darkness. The galaxy’s brightest section begins crossing the meridian to the south by 1:00 am, and you’ll have a great view of the star-clouds in the Summer Triangle of bright stars for the rest of the night.

Jupiter now crosses the meridian at sunset, limiting his best visibility to the late twilight and early dark hours of the night. This still gives you several hours to get a good look at him through the telescope, and the view is still worth your while. The planet’s unique feature, the Great Red Spot, can be seen rotating across the planet’s disc on the evenings of the 13th, 15th, and 18th between 9:30 and 10:30 pm. On the evening of the 19th the Moon Io will cast its shadow on Old Jove’s cloud tops.

Saturn reaches opposition on the morning of the 15th. He will rise at sunset, transit the meridian at 1:00 am, and set at sunrise. Look for an interesting phenomenon a few nights on either side of opposition where the planet’s rings appear noticeably brighter than the ball of the planet. Known as the Seeliger Effect, this is a result of the Sun’s full illumination of ring particles and is similar to the brightening of our Moon at the time of Full Moon.

Venus hangs in the east in the pre-dawn sky. You’ll have no trouble finding her as morning twilight begins to gather. She holds court with the Moon on the mornings of the 20th and 21st.

The Sky This Week, June 6 – 13, 2017 !

The Sky This Week, 2017 June 6 – 13

The Honey Moon brightens the night.
Jupiter, with Ganymede (left), Io (middle), Callisto (top)
and shadows of Io & Ganymede

imaged 2017 June 4, 03:48 UT in poor seeing from Alexandria, Virginia

The Moon dives southward along the ecliptic this week, waxing to the Full phase which will occur on the 9th at 9:10 am Eastern Daylight Time. June’s Full Moon has many popular names: Rose Moon, Strawberry Moon, Mead Moon, and Honey Moon. All of these names describe the somewhat warm tint that Luna takes on as she passes her most southerly declination at the time of the phase. Her light must shine through denser layers of air and atmospheric haze which preferentially scatters blue light, thus her disc appears less blue (or more red). Look for Saturn just south of the Honey Moon on the evening of the 9th.

The bright Moon effectively washes out much of the sky this week, limiting our view to only the brightest stars and constellations. The night gives us a chance to see the last of winter’s stars, Castor and Pollux in Gemini, setting over the western horizon in the fading evening twilight. By 10:00 pm, the brightest object after Jupiter is the rosy-hued star Arcturus, which is high in the south. This star is the brightest star in the northern hemisphere sky. Its prominence is due to its relative proximity to us, located at a distance of about 37 light-years, and its evolution into the red-giant phase of its life. It is a member of a class of stars that form a vast halo around the center of the Milky Way galaxy, and it is currently plunging almost vertically through the galaxy’s plane. It has the largest proper motion of any first-magnitude star visible from our latitude, moving about the apparent diameter of Jupiter over 10 years referenced to more distant background stars.

Almost as prominent as Arcturus are the seven stars that make up the asterism we call the “Big Dipper”. The Dipper makes up about half of the stars that form Ursa Major, the Great Bear, and is one of the most recognized star patterns in the northern sky. Five of the stars are members of a group known as the Ursa Major Moving Group that share a common motion toward a point in the constellation of Sagittarius. Mizar, the star that forms the “bend” in the Dipper’s “Handle”, is an attractive double star in the small telescope. Modern spectroscopy indicates that each component of Mizar is also a double, as is the nearby naked-eye star Alcor. Both Mizar and Alcor are part of the Moving Group and may be bound by gravity. If this is indeed the case, then they form a complex six star system!

By midnight you’ll see the rising stars of the Summer Triangle climbing in the eastern sky. Consisting of the stars Vega, Deneb, and Altair, they will become night-long companions as the warm summer nights take hold in another few weeks.

Jupiter can now be found near the meridian as evening twilight begins to gather. The giant planet should be easy to spot half an hour after sunset, and he provides a fine telescopic target for the next few hours. Old Jove is beginning to resume direct eastward motion against the stars, and over the next several weeks he’ll inch closer to the nearby bright star Spica.

Saturn will reach opposition next week, rising at sunset and setting at sunrise. He transits the meridian shortly after 1:00 am this week, and promises to offer great views of his wide-open rings throughout the summer months.

Venus is the prominent object that early risers see in the morning twilight hours. She will dominate the pre-dawn sky from now until the end of the year.

The Sky This Week, May 30 – June 6, 2017 !

The Sky This Week, 2017 May 30 – June 6

Come to Washington, see the stars!
Moon over Monument: Astronomy Festival on the National Mall
imaged 2014 June 6 at 15th Street & Constirution Ave., Washington, DC

The Moon waxes in the evening sky this week, passing through spring’s subdued constellations before moving into the summer’s sky offerings. First Quarter occurs on June 1st at 8:42 am Eastern Daylight Time. Luna brackets the bright star Regulus on the evenings of May 30th and 31st. You’ll find her very close to Jupiter on the night of the 3rd. On the following night she forms a photogenic triangle with Jupiter and the bright star Spica.

Come down to the National Mall on Friday evening, June 2nd, for the 8th annual Astronomy Festival in the shadow of the Washington Monument. Between 6:00 and 11:00 pm we’ll be offering safe views of the Sun, followed by views of the Moon, Jupiter, and many other celestial objects through telescopes of all sizes. In addition there will be a portable planetarium, talks by leading experts in astronomy and space exploration, as well as exhibits and demonstrations by representatives of leading government and private science and space organizations. Members of local astronomy clubs will be on hand with their telescopes to share the wonders of the night sky and to explain why astronomy can be such a rewarding amateur pursuit. Over two dozen telescopes will ensure that everybody gets a good view. If the weather is good we can expect a turnout of several thousand people. The event takes place on the northeast quadrant of the Washington Monument grounds near the intersection of 15th Street and Constitution Avenue. If it’s raining we’ll have a smaller-scale program at the School Without Walls High School, 2130 G Street, NW.

Among the objects we’ll be looking at on Friday night are double stars. Often overlooked, these star systems make up the vast majority of the stars we can see. To the naked eye almost all stars appear single, but if you use a big enough telescope, spectroscope, or interferometer their dual nature will be betrayed. Understanding the dynamics of double stars is vital to our understanding of stars in general, since the slow changes in their orbital geometry allows us to derive a number of the stars’ physical parameters. Once a double star’s orbit is observed we can use Kepler’s laws to derive the masses of the two stars, and by studying the composition of each star with a spectroscope we can begin to classify them by their colors and masses. We still use our 26-inch “Great Equatorial” refractor, the very same one Asaph Hall used to discover the moons of Mars in 1877, to make nightly observations of double stars. Several are within easy reach of amateur instruments, and some of my favorites are in the current night sky. The easiest to find is Mizar, which forms the “bend” in the “handle” of the Big Dipper. You might be able to discern a faint star near Mizar with your naked eye, but a small telescope reveals Mizar is itself made up of two components. The star Algeiba, which lies just north of the star Regulus in Leo, shows a closely-spaced pair of golden suns. For a challenge look at Izar, which lies 10 degrees northeast of Arcturus. Here you’ll find a closely-spaced pair consisting of a bright yellow and fainter blue companion.

Jupiter will be perfectly placed for the Astronomy Festival, shining down from the stars of Virgo throughout the dark hours of the event. All four of his bright Galilean moons should be visible that night. After the Moon, Old Jove will be the headliner for the evening. His motion against the stars is now almost at a standstill. He will begin to creep back toward the star Spica after June 10th.

We may get a view of Saturn by the end of the Festival evening. The ringed planet now rises before 9:30 pm, but he will remain mired in the haze near the southern horizon.

Look for Venus in the pre-dawn sky. You’ll have no trouble spotting her in the gathering morning twilight. She reaches her greatest elongation west of the Sun on the 3rd. She is currently at her greatest brilliancy for the year, so you can probably follow her into daylight for quite a while after sunrise.

The Sky This Week, May 16 – 23, 2017 !

The Sky This Week, 2017 May 16 – 23

Support the Globe at Night!
Jupiter & its moon Io, imaged 2017 April 27
from Alexandria, Virginia

The Moon climbs northward along the ecliptic in the morning sky this week, passing through the dim constellations of the early autumn sky. Last Quarter occurs on the 18th at 8:33 pm Eastern Daylight Time

This week opens the May campaign for the Globe at Night citizen-science observing program. Initially launched during the 2009 International Year of Astronomy, the program has now compiled thousands of observations from participants in almost 100 countries. The goal of the program is twofold: to raise awareness of the night sky by familiarizing participants with the more prominent constellations, and to map the distribution of global light pollution. In the latter case it is important for people to realize that artificial night lighting has effects far beyond blocking our view of the night sky. More evidence is pointing to the correlation of bright nighttime light and health effects on many species, including our own. Light pollution interferes with circadian rhythms that affect such diverse activities in the animal kingdom as the mass migration of birds and the spawning and hatching of sea turtles. There is also mounting evidence that blue light has very detrimental effects on people, interrupting sleep patterns and possibly affecting our susceptibility to diseases. You can do your part to help science understand these effects by simply going out at night and looking at stars. This month we are featuring the constellation of Leo, the Lion. Leo may be found high in the southwest after the end of evening twilight at around 10:00 pm. Its brightest star, Regulus, forms the base of a “backwards question mark” asterism that is also often called “the Sickle”. This grouping is followed by a right triangle of stars ending in the Lion’s second-brightest star Denebola. From a suburban location I can see the basic stars of the constellation on a good clear night. How many can you see? Go to the Globe at Night website and report your star count!

As evening twilight ends, look high in the east for the bright star Arcturus. This star is only outshone by Jupiter, and it’s easy to locate using the “handle” of the familiar “Big Dipper”. Simply follow the “arc” generated by the curve in the dipper’s handle and “Arc to Arcturus”. This star is the fourth-brightest star in the entire sky and the brightest north of the celestial equator. It is relatively nearby at a distance of just under 37 light-years. Its proximity and its luminosity, which is about 170 times that of the Sun, explain its prominence in our spring sky. It is an old star that is beginning to evolve into its “red giant” phase, and it belongs to a population of similar stars that orbit the center of our galaxy in an enormous halo. Light from Arcturus was used to illuminate a photocell to open the 1933 Chicago World’s Fair.

You can still catch the faint ruddy glow of Mars in the west during the late stages of evening twilight, but you’ll only have a limited window to do so. After keeping ahead of the advancing Sun for several months, the red planet now sets before the sky becomes fully dark.

Jupiter, however, is very hard to miss. The giant planet dominates the evening sky, appearing in the southeast shortly after sunset and crossing the meridian a bit after 10:00 pm. He is located in the constellation of Virgo, and if you’ve been watching him for the past several weeks you will have noticed the increasing gap between Old Jove and the constellation’s brightest star Spica. Binoculars or a small spotting scope will show the planet’s four bright Galilean moons, and larger instruments will begin to reveal details on his cloud-streaked surface. If you have a four-inch or larger aperture instrument try looking for the famous Great Red Spot, which should be prominent on the evenings of the 18th and 23rd.

Saturn will rise at around 10:00 pm by the end of the week, so late-night skywatchers should be able to see him low in the southeast by midnight. The ringed planet will grace the evening sky through the summer months, but right now your best bet to explore his rings and varied moons is by following the Cassini space probe’s mission as it swoops between the rings and the ball of the planet. By the time Saturn leaves us in the fall the probe will have completed its 13-year study, plunging into Saturn’s atmosphere in a grand finale.

Early risers are now being greeted by the bright glow of dazzling Venus. This planet will remain in the morning sky for the rest of the year, adding a bit of extra light to the cooler mornings that will come with autumn’s skies.

The Sky This Week, May 9 – 16, 2017 !

The Sky This Week, 2017 May 9 – 16

The eternal chase
Jupiter & its moon Io, imaged 2017 April 27
from Alexandria, Virginia

The Moon moves into the morning sky this week as she slides into the southern summer constellations. Full Moon occurs on the 10th at 5:42 pm Eastern Daylight Time. May’s Full Moon is popularly known as the Milk Moon, Flower Moon, or Corn Planting Moon in various sky traditions. Look for the Moon to the north of the “head” of Scorpius during the morning hours of the 12th. She’ll be just under five degrees northeast of Saturn in the pre-dawn sky on the 14th.

If you’re following the changing star patterns through the course of the year, this is an interesting time to look at the horizons during the course of the evening. Start by looking southwest at around 9:00 pm. You’ll see the bright stars of Orion, arguably the brightest constellation in the sky, sinking below the horizon. Orion’s signature star, the red-tinted Betelgeuse, is the last star in the group to disappear, setting shortly after 10:00 pm. As Betelgeuse sets, look to the southeast for another ruddy beacon to appear. This is Antares, the brightest star in the constellation of Scorpius. These two luminaries share common characteristics and a connection in the sky lore surrounding their parent star patterns. Both stars owe their red hue to their physical nature as highly evolved “red supergiant” stars. They have exhausted the main supply of nuclear-fusible material in their cores and are fusing heavier elements in shells surrounding an ever-increasing sphere of nuclear “ash”. This causes their outer layers to expand dramatically. If they were placed at the Sun’s position in our solar system their outer layers would swallow up the orbit of the Earth and possibly expand to the orbit of Mars. In fact, Betelgeuse was the first star to have its apparent diameter measured back in 1920, and it was also the first star to be directly imaged using interferometry. Antares is a similar star, with comparable mass and evolutionary history. Both stars are likely supernova candidates and are likely to go out in blazes of glory within the next few hundred thousand years. In mythology, Orion, a demi-god who claimed dominion over all animals on the Earth, boasted of his hunting prowess and his ability to kill any creature. Gaia, the personification of Mother Earth, created the lowly scorpion to punish Orion for his swagger. The creature stung Orion in the heel, killing him. This in turn caused Artemis, goddess of the hunt, to ask her father Zeus to place Orion in the sky. Gaia still had the last laugh, placing the scorpion in the sky as well to pursue Orion around the heavens forever. This is the reason why you will never see the two constellations in the sky simultaneously!

As you watch Orion set, look farther to the north along the western horizon for another ruddy glimmer in the deepening twilight. This is Mars, which has been a fixture in this part of the sky for the past several months. The red planet is pressing eastward against the stars and is presently moving between the bright stars Aldebaran in Taurus and El Nath in Auriga.

Jupiter dominates the evening sky, appearing shortly after sunset high in the southeast. Old Jove is the fourth-brightest object in the sky after the Sun, Moon, and Venus, and you will have no trouble spotting him, even through thin clouds. After the Moon, Jupiter is the most rewarding solar system target for the small telescope. You can spend an entire evening watching the changes in the positions of his four bright Galilean moons with a small telescope. A six-inch or larger instrument will allow you to see changes on the planet itself as Jupiter’s rapid rotation brings new atmospheric features into view over just a few minutes. On the evening of the 11th you can watch the famous Great Red Spot rotate off the planet’s disc as its innermost large moon Io begins to drag its shadow over the cloud tops. You’ll get another good view of the Red Spot on the evening of the 13th.

Saturn now rises at around 11:00 pm, and he’s best seen in the wee hours before morning twilight, crossing the meridian shortly before 4:00 am. The planet’s signature rings are well-presented to our line of sight, and you can see them with almost any kind of optical aid.

Venus shines with her dazzling glow in the morning twilight, rising shortly after 4:00 am. She should remain visible until Old Sol comes up about two hours later.

The Sky This Week, May 2 – 9, 2017 !

The Sky This Week, 2017 May 2 – 9

Scaling the Moon.
The “Three Walled Plains”, lunar craters Arzachel, Alphonsus, and Ptolomaeus
imaged 2016 November 7 with the USNO’s 30.5-cm (12-inch) f/15 Clark/Saegmüller refractor,
1.6X Antares Barlow lens, and a Canon EOS Rebel T2i DSLR

The Moon brightens the evening sky as she moves through the springtime constellations this week, plunging to the southern reaches of the ecliptic.  She waxes from First Quarter to Full Moon, which occurs on the 10th at 9:42 pm Eastern Daylight Time.  Luna spends the evening close to the star Regulus on the evening of the 3rd.  On the 7th she may be found within two degrees of the bright planet Jupiter.

This is another fine week to explore the surface of our nearest celestial neighbor.  The Moon is an ideal target to explore with virtually any kind of optical aid.  It was a view of the Moon through my father’s binoculars at the age of seven that whetted my interest in astronomy, and it is still a great way to introduce anyone to the fascination that is inherent in space exploration.  The slightest magnification transforms the Moon from a glowing object in the sky to a place, one that has topography in mountains and craters and their associated shadows.  These land forms are unlike anything that we routinely experience on Earth, and they are further accentuated by the absolute starkness of the shadows which look as if they were painted with India ink.  While the craters may appear to be small in small- to modest-aperture telescopes, their true size is masked by the nearly quarter-million mile distance of Luna’s surface from us.  Even in our venerable 12-inch telescope here at the Naval Observatory the smallest features we can see on the Moon are about the size of Meteor Crater, about 40 miles east of our Flagstaff Station.  That earthly impact feature, about one kilometer across, would barely be visible if our telescope were located on the Moon.  That means that the craters that look impressive in our eyepieces are truly enormous.  Most of the craters in the Moon’s battered southern region have diameters that measure in the tens of kilometers/miles and more.  Look at the picture we’re featuring this week.  The three prominent craters to the right of center will be well-placed for viewing on the evening of the 3rd and following evenings.  Closest to the center is Arzachel, named for a 12th Century Persian astronomer.  It is 97 kilometers (59 miles) across.  Next to it is Alphonsus, named after King Alfonso X of Spain, whose 13th Century planetary tables were widely used until the time of Kepler.  It is 118 kilometers (71 miles) from rim to rim and was the target of the Ranger 9 lunar “hard lander”.  The largest and oldest of the “Three Walled Plains” is Ptolomaeus, named after the Greek astronomer Claudius Ptolemy, author of The Almagest, one of the first epic treatises on astronomy.  It is 154 kilometers (93 miles) across, roughly the distance from Washington to Richmond, Virginia!

Mars continues to loiter in the western sky, but you’ll have to contend with deepening twilight and atmospheric haze to see him.  He is gradually losing his year-long race with the Sun, but he will still be about 10 degrees above the western horizon at 9:00 pm.  This week he glides to the north of the bright star Aldebaran in Taurus.

Jupiter is well-paced for viewing as evening twilight fades to darkness.  The giant planet crosses the meridian just after 11:00 pm EDT, so you have all of the evening hours to view him through the telescope.  On the evening of the 4th you can watch the moon Io drag its shadow across the planet’s disc between 9:00 and 10:00 pm.  On the evening of the 6th the Great Red Spot will be ideally placed for evening views.  On the 9th you can watch Jupiter’s largest moon, Ganymede, emerge from the planet’s shadow at 10:50 pm, joining its other three companions in an unusually tight formation around the hulking planet.

Saturn rises at around 11:00 pm by the end of the week, but your best view of him will still be before the onset of morning twilight.  Despite the fact that his rings are tipped close to their widest presentation toward us, the planet never gets higher than 30 degrees above the southern horizon.  You’ll need very steady morning air to see their finer details.

Venus greeted me at 5:30 this morning, as she now greets many of my fellow dog walkers.  You’ll be hard-pressed to miss her if you’re up before the Sun.