The Sky This Week, October 1 – 8, 2019 !

The Sky This Week, 2019 October 1 – 8

A night to celebrate the Moon!
The Moon, imaged 2019 July 11 from Alexandria, Virginia.
The Moon at age 8 days, imaged 2019 July 11 from Alexandria, Virginia
with a 102 mm (4-inch) f/6.5 Explore Scientific refractor and a Canon EOS Rebel SL2 DSLR.

The Moon wends her way through the southern part of the sky this week, passing the bright planets Jupiter and Saturn before moving into the autumnal constellations.  First Quarter occurs on the 5th at 12:47 pm Eastern Daylight Time.  Luna meets up with bright Jupiter on the evening of the 3rd.  On the night of the 5th she may be found close to golden Saturn.

October is generally one of my favorite months for observing the night sky.  The weather tends to be clear, the summer’s humidity is all but a memory, the nights aren’t too cold, and the sky is fully dark at a decent hour.  These are the main reasons that the United Nations has designated October 4 – 10 as World Space Week.  This year’s theme is “The Moon:  Gateway to the Stars”, and appropriately October 5th is International Observe the Moon Night.  Throughout the world amateur observers and professional observatories will open their domes to the public to showcase our only natural satellite.  Here in the Washington, DC area there will be a number of venues to get a good look at the Moon.  The University of Maryland will host an open house at its observatory in College Park, MD, while the National Capital Astronomers will have telescopes set up for public viewing near the Nature Center in Rock Creek Park in DC.  Also in DC, the Phoebe Waterman Haas Public Observatory at the Smithsonian’s National Air & Space Museum will be open for lunar views from 7:00 pm until 10:00 pm.  The Northern Virginia Astronomy Club will host its 37th annual Star Gaze at C.M. Crocket Park in Fauquier County, Virginia.  While this day-long event is free, the park has a nominal entry fee.  In all of these events the Moon will be the main attraction, but participants at the NOVAC Star Gaze will also have the chance to see many other celestial objects through a variety of telescopes.  Outside the Washington DC area there will be observing events at science centers and planetariums throughout the country and the world.  Why the Moon?  It is our closest neighbor in space at some 385,000 kilometers (239,000 miles) distance.  Despite this great distance telescopes reveal an astonishing variety of landscapes on Luna’s desolate surface that bear mute testimony to the violent collisions of proto-planetary bodies as the solar system formed.  Take advantage of this opportunity; it only comes once a year!

While the Moon gradually comes to dominate the early evening sky, the late night still affords a chance to view the splendors of the late summer constellations and the rising stars of winter.  From a dark sky site the Milky Way crosses overhead, stretching from the southwest to the northeast horizons.  Sprinkled along the Galaxy’s path are the bright stars of the Summer Triangle, the “W”-shaped constellation of Cassiopeia, the Queen, and the “wishbone” formed by the stars of Perseus, the Hero.  If you follow the left-hand “tine” of the wishbone, you will see a familiar sight of the winter sky rising in the form of the Pleiades star cluster.  Most of us can see six or seven stars in this small grouping, but if you happen to be blessed with sharp eyesight and are under a really dark sky about a dozen stars will reveal themselves.  Look at the Pleiades through binoculars and a dozen more stars will appear, and a good four-inch telescope will bring the count up to around 100!  At a distance of 440 light-years, this is one of the closest galactic star clusters to us.  One of the most striking features of the cluster are its brightest stars, which glow with an icy-blue tint.  These are some of the youngest stars we know of, and they likely formed from a vast cloud of gas and dust some 100 million years ago.  Long-exposure images of the Pleiades show wispy clouds of nebulosity suffused throughout the cluster, the remnants of the cloud of material that formed its stellar cohort.  Despite its diminutive size, the Pleiades cluster figures prominently in the sky lore of just about every culture that can see it.  Even the denizens of J.R.R. Tolkien’s Middle Earth recognized the cluster, calling it “Remmirath”, the “Netted Stars”.

The early evening still hosts the bright glow of Jupiter, but not for very long.  The giant planet sets at around 10:00 pm, so your “window” to see him is becoming more limited.  The best time to get a look at him through the telescope will be during evening twilight before he gets too low and suffers distortion from turbulence in our atmosphere.

As evening twilight fades you will find Saturn just west of the meridian.  The ringed planet still offers a couple of hours of good viewing time before he heels over to the southwestern horizon.  Saturn will be close to the Moon on the 5th, so if you’re attending one of the Observe the Moon Night activities he will add a cosmic bonus to your observing list.


The Sky This Week, September 24 – October 1, 2019 !

The Sky This Week, 2019 September 24 – October 1

The stories the stars can tell
NGC 869 & 884, the Perseus Double Cluster, imaged 2018 October 7 from Mollusk, Virginia.
NGC 869 & 884, the Perseus Double Cluster, imaged 2018 October 7 from Mollusk, Virginia
with a 102 mm (4-inch) f/6.5 Explore Scientific refractor and a Canon EOS Rebel SL2 DSLR.

The Moon frames the weekend with her waning and waxing crescent phases this week.  New Moon occurs on the 27th at 11:38 pm Eastern Daylight Time.  She has been a striking sight in the pre-dawn sky for the past several days, greeting me each morning when I go out to retrieve the morning paper.  Look for the Moon’s crescent close to the bright star Regulus before sunrise on the morning of the 26th.

The first full week of autumn presents another opportunity to enjoy cool crisp evenings under the stars while doing a bit of “citizen science” on the side.  The Globe at Night program’s monthly observing campaign once again features the constellation of Cygnus, the Swan for its September target.  Cygnus should be readily identifiable since it passes directly overhead at around 9:00 pm EDT.  Its brightest star is Deneb, easternmost and faintest of the three bright stars than comprise the Summer Triangle asterism.  Deneb marks the Swan’s tail, and his long neck terminates in the third-magnitude star Albireo, which lies about halfway between Vega and Altair, the Triangle’s other bright stars.  Between Deneb and Albireo are three stars that lie perpendicular to the Deneb-Albireo line, forming a large cross-shaped figure that makes an acceptable stick-figure Swan.  This pattern should be visible from most suburban skies, but the view from a dark location is truly breathtaking.  Fainter stars trace out the gentle sweep of Cygnus’ wings, and the soft glow of the Milky Way directs the Swan’s path to the south.  The figure of the Swan reflects the Greco-Roman mythology that dominates the constellations as we know them today, but other cultures see the same patterns in different ways.  One of my favorite bits of sky lore for this constellation comes to us from the Inuit people of the arctic regions.  They see a man in a kayak paddling his craft along the “Pebbly River” of the Milky Way.  Whatever figure you choose to see, take some time this week to find Cygnus and compare your view with charts on the Globe at Night website.  Give your eyes some time to adapt to the darkness, and try to observe from a spot that’s not in the direct illumination from streetlights.  Your observations will help scientists track the spread of light pollution, which is gradually robbing us of our night skies as well as causing disruption to the circadian rhythms of nocturnal animals, birds, and even humans.

By midnight the Summer Triangle occupies the western sky while another geometric figure begins to cross the meridian.  This figure forms an almost perfect square of second-magnitude stars and marks the body of Pegasus, the mythical winged horse of Greek mythology.   Pegasus is one of several related constellations that grace the autumnal sky.  Draw a northward line through the stars on the left side of the square to find the “W”-shaped constellation of Cassiopeia, the Queen.  According to the Greeks, she was a very vain queen, constantly admiring herself in a mirror.  One day she claimed that her beauty surpassed that of the Sea Nymphs, the consorts of Poseidon, god of the oceans.  Poseidon decided to punish the queen by chaining her daughter Andromeda to a rock to be devoured by a fearsome sea monster.  You can see Andromeda’s chains diverging from the upper left corner of the square, marked by the star Alpheratz.  Fortunately, the hero Perseus arrives on Pegasus, kills the monster, and saves the vain queen’s daughter!  Perseus lies just to the northeast of Cassiopeia and is anchored by the bright star Mirfak.  To me the constellation resembles the part of a broken wishbone that the “winner” gets.  The area between Perseus and Cassiopeia is one of the best parts of the sky to scan with binoculars or small telescopes.  The bright star Mirfak is surrounded by a scattered group of fourth- and fifth-magnitude stars that form a loose galactic star cluster known as Melotte 20.  It is located about 560 light-years away.  Buried in the Milky Way between Cassiopeia and Perseus is one of my favorite objects in the entire sky, the “Double Cluster”.  Visible as a pair of fuzzy knots of light in binoculars, its true splendor is revealed in small telescopes of 3- to 4-inch aperture.  View it from a dark site for a truly spectacular experience.

Jupiter continues to hold court in the early evening sky, appearing in the southwest as twilight falls.  Despite his far southerly declination Old Jove remains the brightest object in the evening sky until he sets at around 10:30 pm.  If you want to get a decent view of him in the telescope point your instrument at him as soon as you can see him in twilight.  Atmospheric turbulence will degrade the clarity of his image as he heads toward the southwest horizon.

Saturn crosses the meridian shortly after sunset, and should become visible in deep twilight by 8:00 pm.  The ringed planet is best observed before 10:30 pm, when he, too, will follow Jupiter toward the southwest horizon.  He sets at around midnight, leaving the sky bereft of bright planets for the rest of the night.

The Sky This Week, September 10 – 17, 2019 !

The Sky This Week, 2019 September 10 – 17

It’s time for the Harvest Moon
Saturn and six moons, imaged 2015 July 12 at the U.S. Naval Observatory.
Saturn and six moons, imaged 2015 July 12 at the U.S. Naval Observatory
Composite image made with the 30.5-cm (12-inch) f/15 Clark/Saegmüller refractor.
and a ZWO ASI120MC color imager. Note Titan to the upper right.

The Moon climbs through the dim autumnal constellations this week, reaching her Full phase on the 14th at 12:33 am Eastern Daylight Time.  As the Full Moon that occurs closest to the autumnal equinox, this particular Full Moon is almost universally known as the Harvest Moon, at least in Northern hemisphere climes.  It gets this name due to the unusual geometry of the Moon’s path through the sky at this time of the year.  If you follow the Moon’s progress around the sky each month, you will note that she advances about 13 degrees on successive nights.  On average, the time between successive moonrises in northern temperate latitudes is about 50 to 60 minutes, but around the times of the equinoxes the angle that the plane of the Moon’s orbit makes with the eastern horizon reaches its extremes.  In the spring it intersects the eastern horizon at a high angle, so times of successive moonrises of the nearly Full Moon differ by up to 80 minutes.  In the fall the opposite effect takes place, with Luna’s orbit intersecting the horizon at a much shallower angle.  Now the times of successive full moonrises differ by just 30 minutes.  This effect becomes more pronounced as you move to higher northern latitudes.  Throughout most of Europe, where the annual harvest season is in full swing, the Full Moon rises only 20 minutes later each night.  If you venture north of the Arctic Circle, the Moon will actually rise earlier on successive nights.  This annual effect was not lost on farmers in bygone times.  Having the nearly Full Moon rise at nearly the same time each evening at peak harvest time enabled them to work well past sunset to bring in their reapings.

The bright Moon washes out all but the brightest stars in the evening sky.  Most of the eastern sky appears blank, populated by the dim constellations of Capricornus, Aquarius, Cetus, and Pisces.  With the exception of the second-magnitude star Diphda in Cetus, none of these star patterns boast stars brighter than third-magnitude.  However, there is one star that stands out from the retinue of faint stars.  You’ll find it located low in the southeast during the later evening hours, a lonely beacon in an otherwise near-empty sky.  This star is Fomalhaut, brightest star in the obscure constellation of Pisces Austrinus.  It is the 19th brightest star in the sky, and its isolated position makes it a useful navigation reference for interplanetary spacecraft.  For many years its spectrum has been used as a standard reference to study other stars.  Located at a distance of about 25 light-years, it began to garner intense interest by astronomers in the mid-2000s.  Infrared studies revealed that Fomalhaut was surrounded by a pair of flattened discs of cool material that were thought to be proto-planetary in nature, similar to the Kuiper Belt that encircles the Sun beyond the orbit of Neptune.  In November, 2008 it was announced that the Hubble Space Telescope had imaged a planetary companion to the star, the first direct image of a planet orbiting a star other than the Sun.  Since that time new observations indicate that at least two other planets also circle Fomalhaut, and it joins the star Castor as the only first-magnitude stars known to host planetary systems.

While Fomalhaut skirts the southern horizon, the bright stars of the Summer Triangle pass across the zenith.  Vega, Deneb, and Altair should be easy targets to spot despite bright moonlight and urban light pollution.  You can use these stars to find a number of interesting things to look at with a small telescope despite the brightness of the sky.  Near the center of the triangle, about halfway between Vega, the brightest of the trio, and Altair, the southernmost, lies a third-magnitude star that you may be able to glimpse with the naked eye on a crisp evening.  This is Albireo, the star that marks the “head” of Cygnus, the Swan.  Point a small telescope at Albireo and you will be rewarded with a view of a wide double star whose components exhibit a striking color contrast.  The brighter component shines with a golden yellow hue, while the fainter member is distinctly blue.  Because of this I like to call Albireo the “Navy Double”.  This is a sight that’s best enjoyed in small telescopes.  In larger instruments the colors tend to wash out.

Jupiter continues to dominate the southwestern sky in the early evening.  The giant planet is gradually inching eastward against the stars of Ophiuchus, the Serpent Bearer.  In addition to the changing surface features of the planet itself, the comings and goings of his four bright Galilean moons are also interesting to watch.  If you happen to be watching Old Jove in your telescope at 8:06 pm EDT on the evening of the 16th, watch the largest moon Ganymede emerge from the planet’s shadow well to the east of the bright planetary disc.

Saturn crosses the meridian at around 8:30 pm, offering several hours of telescopic inspections before he sinks toward the southwest horizon.  Haze and bright moonlight will hamper your search for some of the planet’s bevy of icy moons, but you should be able to spot Titan, the largest of these companions.  Titan is unique in the solar system because it has a dense atmosphere, but you probably wouldn’t want to visit.  Titan’s weather consists of downpours of liquid methane and blizzards of frozen ethane, and it is very cold at 94° Kelvin (-290°F)!

The Sky This Week, September 3 – 10, 2019 !

The Sky This Week, 2019 September 3 – 10

A fall reprieve for summer’s stars
The Summer Triangle rising, imaged 2019 July 5 at Mollusk, Virginia.
The Summer Triangle rising, 2019 July 5
imaged made with a Canon EOS Rebel SL2 DSLR from Mollusk, Virginia.
The bright stars Vega (upper left), Altair (lower right) and Deneb (lower left)
are embedded in the Milky Way.

The Moon spends the week skirting the southern horizon, waxing from crescent to gibbous phase as she passes through the southern summer constellations.  First Quarter occurs at 11:10 pm Eastern Daylight Time.  Luna may be found northeast of bright Jupiter on the evening of the 5th.  She may near golden Saturn on the nights of the 7th and 8th.  By the end of the week she sets out across the dim autumnal constellations.

If you’re following the progress of the Sun, you’ve probably noticed that the times of sunrise and sunset are changing quite rapidly.  As we approach the autumnal equinox, the rate at which these quantities change reaches its maximum, and the overall length of day now decreases by up to three minutes per day.  As September opens the length of day is about 13 hours, and by the month’s end it will be 70 minutes shorter.  I particularly notice this in the mornings, as I now find that my alarm goes off well before the Sun comes up.

As the time of sunset moves earlier in the evening it offers a bit of a reprieve for the summer constellations.  As the Earth orbits the Sun we see the constellations change incrementally throughout the year.  A given star will rise four minutes earlier on each successive evening, which means that it will set four minutes earlier as well.  However, with the time of sunset occurring almost two minutes earlier each evening the summer stars seem to linger, setting only two minutes later with respect to Old Sol.

The summer Milky Way gradually erodes as the waxing Moon casts more light as the week progresses.  Fortunately you can trace the course of the galaxy through the sky by looking for the bright stars scattered from the southwest to the northeast along its path.  Just below and to the right of bright Jupiter is the ruddy star Antares, the “heart” of Scorpius, the Scorpion.  If you have a good view of the southwest horizon look for the other stars that delineate this prominent constellation.  The Scorpion’s “tail” is marked by a naked-eye pair of stars, Lesath and Shaula.  Above and to the left or these is a grouping of stars that resemble a teapot with the “spout” tilted toward the pair.  This is the most recognizable part of the constellation of Sagittarius, the Archer.  The planet Saturn lies just to the left of the teapot’s “top”.

High overhead you’ll find the stars of another large asterism, the Summer Triangle.  Each of these stars belongs to its own constellation.  Vega, brightest and westernmost of the Triangle, leads a small parallelogram grouping that represents the Lyre of Orpheus in Greek mythology.  Vega is one of the closer stars to the solar system, shining from a distance of 25 light-years.  Just east of Vega binoculars will show a closely-spaced pair of stars, Epsilon 1 and Epsilon 2 Lyrae.  This pair is a good test of resolving power for small telescopes; a good 3-inch telescope will resolve each component into a close pair.

The southernmost star in the Triangle is Altair, which is the central star in the constellation of Aquila, the Eagle, which carried thunderbolts for Zeus in mythology.  Altair is just under 17 light-years distant, and is one of the closest bright stars to the Sun.

The Triangle’s third and faintest star is Deneb, which marks the “tail” of Cygnus, the Swan.  Although it outwardly appears that Deneb is comparable to its companions, it is altogether a different kind of star.  Both Vega and Altair are bright because of their relative proximity in space, but Deneb is bright because it is one of the most luminous stars in the galaxy.  Its distance is about 2500 light years, so in order to appear as bright as it does over that vast stretch of space it shines with the radiance of over 200,000 Suns!

Jupiter is still well-placed for evening perusal.  You’ll see the giant planet appear just west of the meridian about 20 minutes after sunset, and for the next couple of hours he dominates the southwestern sky.  By 8:30 pm you should have a clear view of him in the telescope, and you should have well over an hour to enjoy the view before he begins to sink into the horizon haze.

Saturn follows Jupiter, crossing the meridian at around 9:00 pm.  Take some time to give Saturn a good look through the telescope.  On evenings when the atmosphere is steady, a modest instrument should show a nice view of the structure in the planet’s mysterious rings.

The Sky This Week, August 27 – September 3, 2019 !

The Sky This Week, 2019 August 27 – September 3

A sky for three seasons.
The Old Moon in the arms of the New Moon, imaged 2018 January 20 at Alexandria, Virginia.
“The Old Moon in the arms of the New Moon”
HDR image made 2018 January 20 with an Explore Scientific AR102 102mm (4-inch) f/6.5 refractor telescope
and a Canon EOS Rebel SL2 DSLR from Alexandria.

The Moon begins the week as a slender waning crescent visible just before sunrise and returns to the early evening sky by the week’s end.  New Moon occurs on the 30th at 6:37 am Eastern Daylight Time.  This is the second New Moon for the month of August.  Having two primary lunar phases occur in the same calendar month is not particularly unusual, occurring once or twice each year.  In 2020 April will have two First Quarter phases, and October will have two Full Moons.  This week look for the waxing crescent Moon near the bright star Spica in the early evening hours of September 1st and 2nd.

The August campaign for the Globe at Night citizen-science continues through the end of August.  This month’s target constellation is Cygnus, the Swan, which we highlighted last week.  If you are away from the city for the upcoming holiday weekend take a few moments to let your eyes adapt to the darkness, then look for the constellation and contribute your observations to the program’s website.  You’ll find Cygnus near the zenith at around 10:00 pm local time.

As August transitions to September we start to see the stars of late spring heeling over to the west while the first stars of autumn ascend in the east.  At 10:00 pm the bright springtime beacon of the star Arcturus flickers over the western horizon.  This is the brightest star in the northern hemisphere and the fourth-brightest in the entire sky.  Its rosy tint is due to its relatively cool surface that has been inflated by its evolution into an older star.  It has exhausted the hydrogen in its core so the fusion reactions that sustain its light output now come from a slowly expanding shell that is causing its diameter to grow to about 25 times that of the Sun.  Watch Arcturus as it dips toward the horizon.  As its altitude decreases its light must shine through more and more of Earth’s atmosphere, causing it to “twinkle” with increasing ferocity.  It’s not unusual to see it cycle through all of the colors of the rainbow as it nears the horizon and sets at around midnight.

At 10:00 pm the bright stars of the Summer Triangle pass directly overhead, highlighting the constellations of the summer sky.  Bisecting the Triangle is the soft glow of the Milky Way.  From a dark site you can see this faint river of diffuse light arcing from the southwest to the northeast, punctuated by the light of brighter stars.  The constellation of Scorpius dominates the southwestern sky, highlighted by the ruddy star Antares.  This star is even more evolved than Arcturus, and its diameter is over 700 times that of the Sun!  To the northeast look for a small group of second-magnitude stars that resemble the letter “W”.  This is Cassiopeia, the queen of Ethiopia whose vanity resulted in a classic tale from Greek mythology that we’ll highlight in a few more weeks.

Looking to the east, a large square asterism is now climbing higher as the nights pass.  This easily recognized asterism is part of the constellation of Pegasus, the mythical Flying Horse that also figures prominently in the Cassiopeia tale.  Seeing this constellation climbing into the evening sky is one of the signs that tells me that cool autumn nights are on the way with the promise of more clarity than the hazy nights of summer.  The “Great Square” is also a good indicator of the darkness of your local sky.  From most urban and suburban locations you probably won’t see any stars inside the square, while rural skies will reveal at least half a dozen between the four corners.

Jupiter beams down in the southwestern sky during the evening hours.  He is hard to miss since he is the brightest object in the sky after the Moon.  He is slowly beginning to resume direct motion eastward against the stars, and over the next few weeks you can gauge his progress as he edges away from the star Antares.  By this time next year he will be closing in on Saturn.

Saturn lingers just east of the top of the “Teapot” asterism of Sagittarius.  The ringed planet crosses the meridian just before 10:00 pm, offering you many hours to enjoy a view of his famous appendages.

The Sky This Week, July 30 – August 6, 2019 !

The Sky This Week, 2019 July 30 – August 6

Wading in the Milky Way’s Lagoon.
Messier 8, the Lagoon Nebula, imaged 2014 July 5 from Morratico, Virginia.
Messier 8, the Lagoon Nebula, imaged 2014 July 5
with an 80 mm (3-inch) f/6 Antares Sentinel refractor and a Canon EOS Rebel T2i DSLR
from Morattico, Virginia.

The Moon returns to the evening sky this week, with her waxing crescent moving through the departing constellations of the late springtime.  First Quarter occurs on August 7th at 1:31 pm Eastern daylight Time.  Look for the Moon a few degrees north of the bright star Spica on the evening of the 5th.

As August opens we enter a period of enhanced meteor activity.  Currently there are a couple of minor showers, the Southern Delta Aquariids and the Alpha Capricornids that are reaching their peak activity.  Neither one is a “show-stopper”, but observers at dark locations may see up to 20 meteors per hour from radiants in the southeast in the hours before sunrise.  Also active is the annual Perseid shower, which is gradually building towards its peak on the night of August 12-13.  The radiant for the Perseids rises in the northeast at around 11:00 pm, but the best activity once again occurs in the early morning hours.  The Perseids can be very productive at their peak, producing up to 100 meteors per hour at their peak.  Unfortunately this year the 94% illuminated Moon will wash out much of the activity on the peak night, but for the upcoming week they should produce decent numbers after midnight.

August is one of my favorite months for stargazing.  The nights are gradually growing longer, so we don’t have to wait as long to start enjoying the splendors of the summer sky.  At the end of evening twilight one of the season’s signature constellations may be seen in all its glory as it crosses the meridian in the southern sky.  Scorpius is one of the most distinctive stellar groups in the sky, rivalling its winter counterpart of Orion.  Both constellations share similar elements, with most of their stars formed in physical associations.  Each constellation also has a “red supergiant” star as their most prominent luminaries.  Antares in Scorpius and Betelgeuse in Orion are highly evolved stars that are near the end of their evolutionary tracks.  These stars have distinctive reddish tints, indicating a relatively cool surface, but both stars are gargantuan in size.  If they were placed in the Sun’s position in our solar system Betelgeuse would engulf the orbit of the Earth, while Antares would swallow up Mars!  In mythology Orion and Scorpius are mortal enemies, so they are on opposite sides of the sky.  Thanks to this arrangement you will never see Antares and Betelgeuse in the sky at the same time.  Scorpius is one of the few constellations that looks like its namesake, and for Northern Hemisphere observers this is the best time of year to see it.  My favorite feature of Scorpius is the “fish hook” asterism formed by its southernmost stars that ends in a close pair of blue-hued stars that mark the Scorpion’s stinger.  Known as Shaula and Lesath, this naked-eye pair was called the “Swimming Ducks” by the Skidi Pawnee of the American Midwest.

Rising upward from Scorpius are the rich star clouds of the summer Milky Way.  By 11:00 pm the luminous band of our home Galaxy arcs high over the eastern horizon.  One of the most striking features of the Milky Way are the seeming “voids” that bisect it from the stars of the Summer Triangle down to the southern horizon.  Far from being empty space, these dark regions are teeming with cold dust and gas that obscures the light of more distant stars.  The stuff that makes up these dark clouds is the very stuff that stars and planets are formed by.  Dotted here and there along the Milky Way you’ll find glowing patches of light against the dark clouds.  These are areas where stars are forming.  One of the easiest to find is Messier 8, also known as the Lagoon Nebula.  You can find it as a misty patch of softly glowing light in a pair of binoculars about halfway between Jupiter and Saturn.  Sweep northeastward along the Milky Way and you will encounter several more of these glowing knots, proof that our galaxy is still very busy making stars.

Jupiter crosses the meridian at the end of evening twilight, offering you the best view of the giant planet as darkness falls.  Try to get him in the telescope at this time; as the night progresses he will start losing altitude as he moves into the southwestern sky.  On the evening of August 2nd you should have a great view of the planet flanked by his four Galilean moons.  They will be far enough from the planet to be visible in binoculars.

Saturn crosses the meridian at around 11:30 pm, so once you’ve finished looking at Jupiter you’ll have plenty of time to view the ringed planet.  Saturn is one of the most spectacular objects that you can view in the sky.  When people see it for the first time they usually don’t believe their eyes.  Often I’ll hear comments from people at star parties expressing disbelief, eliciting a variety of interesting comments.  My favorite is “Wow, it looks just like the pictures!”  The “live” view is way better than any image, though.  When you see its distinctive outline suspended in the eyepiece, it is currently some 1.36 billion kilometers (845 million) miles away and you are seeing it as it was 75 minutes ago!

The Sky This Week, July 23 – 30, 2019 !

The Sky This Week, 2019 July 23 – 30

Hanging out with Hercules.
Messier 13, the Hercules globular cluster, imaged 2013 August 5 from Fishers Island, New York.
Messier 13, the Hercules globular cluster, imaged 2013 August 5
with an 80 mm (3-inch) f/6 Antares Sentinel refractor and a Canon EOS Rebel T2i DSLR
from Fishers Island, New York.

The Moon wanes in the pre-dawn sky this week, climbing northward along the ecliptic, joining the first rising stars of the winter sky.  New Moon occurs on July 31st at 11:2 pm Eastern daylight Time.  Early risers can watch Luna’s dwindling crescent pass by the bright star Aldebaran in the pre-dawn skies of the 27th and 28th.

The Moon’s absence from the sky offers us another opportunity to take in the wonders of the summertime sky.  It also gives you a chance to do a little “citizen science”.  The Globe at Night program returns for its July installment this week, inviting skywatchers to look for stars in prominent constellations to gauge the brightness of the night sky.  This month’s featured constellation is Hercules, which you will find nearly overhead as evening twilight ends.  Hercules is the second-largest of the classical constellations delineated by Ptolemy, and his most prominent feature is a four star asterism popularly known as “The Keystone”.  You’ll find this distinctive pattern about one-third of the distance between the bright blue star Vega in the east and the rose-tinted springtime star Arcturus in the west.  If we imagine the Keystone as the hero’s torso, his extremities straggle off to the north and south.  To help with the Globe at Night project, simply go to their websiteand follow their directions to record an observation.  When we look just east of the stars of the Keystone, we are looking along the direction that the Sun and its gaggle of planets, moons, and asteroids are headed as we drift through our local spiral arm of the Milky Way galaxy.  Referenced to the more distant stars we are moving at a velocity of around 48,000 kilometers (30,000 miles) per hour.  From a dark-sky site Hercules offers one of the most spectacular “deep sky” objects in all the sky.  If you use a pair of binoculars, look between the two stars that form the western side of the Keystone for a fuzzy knot of light.  A telescope of four inches aperture will begin to resolve this knot into a swarm of faint stars, and the more you increase the telescope aperture the more it resolves into a myriad of luminous pinpoints.  The view through my 14-inch reflector is simply breathtaking, and I will often spend an hour or more poring over the object’s fine details.  Known as Messier 13, it is a fine example of a globular star cluster.  Globular clusters surround the central bulges of many spiral and elliptical galaxies, and they may be the remnant cores of dwarf galaxies that swept through the planes of their larger galactic hosts.  We find many such objects in the summer sky, a time when our galactic center is in full view.

The summer Milky Way takes center stage in the overnight hours.  Our home galaxy is a huge flattened disc of stars that spans some 200,000 light-years and contains roughly 200 billion stars.  Our Sun is in the galactic “suburbs”, some 30,000 light-years from its center.  While its visual appearance is that of a more or less continuous band of amorphous light, exploration with radio telescopes reveals its structure of spiral arms wrapping around its central bulge.  As we look toward the southern horizon we are looking in the direction of the galactic center, and you can see a noticeable widening of the glowing band just above the “teapot” asterism of Sagittarius.  However, we can’t actually see the center in visible light; a huge wall of opaque gas and dust obscures our direct view of this feature.  You can see some of this obscuring material in the form of the “Great Rift” that runs from the center of the Summer Triangle down to the horizon.  Fortunately astronomers have developed instruments that can observe the center in any different wavelengths, and the structures that they have revealed are truly mind-boggling.  X-ray and radio telescopes have revealed a very compact, highly energetic energy source which we now believe to be a super-massive black hole.  This object contains the equivalent mass of over 4 million Suns!

Jupiter shines brightly in the south during the evening and overnight hours.  The giant planet crosses the meridian at around 10:00 pm, so you’ll have ample time to give him a good look with binoculars or telescopes.  Low power scopes and binoculars are sufficient to follow the motions of his four bright Galilean moons, while instruments of four or more inches of aperture will reveal details on the planet’s gaseous face.  The prominent equatorial cloud belts will break up into a myriad of swirls and eddies in large-aperture instruments, and these features will change dramatically from night to night.

Jupiter is trailed by Saturn, which doesn’t glow as brightly as Jupiter but is still easy to spot as darkness falls.  The ringed planet is located just east of the “teapot” of Sagittarius, and anyone who points a telescope in his direction will be in for a treat.  The planets rings, composed of billions of ice particles, are as wide-open to our line of sight as they can get and will reveal themselves in a simple spotting scope.  Put a larger aperture on Saturn and the rings will begin to show detail.  You’ll also see more of the planet’s many icy moons.  Titan, the planet’s largest and brightest moon, is one of the most interesting bodies in the solar system.  It has a substantial atmosphere of nitrogen, methane, and other complex carbohydrates.  The Cassini orbiter, which circled Saturn for over 13 years, revealed that Titan has oceans of liquid methane on a surface of hard water ice.  What a strange world to stoke the imagination!