The Sky This Week

The Sky This Week, 2021 January 19-26

The Moon, Sinus Iridum and Plato region, imaged at the U.S. Naval Observatory on 2012 February 6, 23:58 UT.
The Moon, Sinus Iridum and Plato region, imaged at the U.S. Naval Observatory on 2012 February 6, 23:58 UT
with the 30.5-cm (12-inch) f/15 Clark/Saegmüller refractor, 1.6X Antares Barlow lens, and a Canon EOS Rebel T2i DSLR.

The Moon climbs higher in the evening sky this week, passing through the winter constellations as she waxes toward her full phase.  First Quarter occurs on the 20th at 4:02 pm Eastern Standard Time.  Look for Luna near ruddy Mars on the evenings of the 20th and 21st.  On the 23rd she passes north of the bright star Aldebaran in the constellation of Taurus, the Bull.  

This is another good week to do some Moon-watching.  As Luna climbs higher along the ecliptic her light passes through less of Earth’s atmosphere, offering less turbulence to blur details on her surface.  As she waxes into her gibbous phases two dramatically different landscapes are revealed.  The two largest of her ancient impact scars contrast with the battered terrain of the “southern highlands”, where craters stand shoulder-to-shoulder as a testament to the violence of the early solar system.  The two large basins known as the Mare Imbrium (Sea of Rains) and Oceanus Procellarum (Ocean of Storms) appear relatively flat compared to the pockmarked highlands.  However, they were produced by collisions with large proto-planets billions of years ago.  Molten rock from the lunar mantle eventually flooded these vas basins, solidifying well after the age of intense bombardment that created the highlands.  The few craters that dot the surfaces of these so-called “seas” were created relatively recently on the lunar time-scale, falling within the last 3.5 billion years or so.  Owners of small telescopes can delight in these features as the terminator line slowly advances across the Moon’s face.  

One of my favorite features on the Moon will be well-placed for viewing on the evening of the 23rd.  By this time the full extent of the Mare Imbrium will be revealed.  This vast circular feature is 1250 kilometers (775 miles) in diameter and is surrounded by a series of tall mountain ranges.  On its northwestern side the ring of mountains is interrupted by a semi-circular feature known as Sinus Iridum, the Bay of Rainbows.  This was one of the first lunar features I identified with my first telescope, and I always like to come back to it when it is visible.  Another striking feature sits along the northern edge of Mare Imbrium, the dark-floored crater Plato.  This 100-kilometer (60-mile) feature is an ancient crater that was flooded with lava.  Its flat surface is pocked with small craterlets; viewing these is a challenge for your telescope’s optics.

Luna’s brightening glow gradually swallows up all but the brightest of the season’s stars, but fortunately Mother Nature has seen fit to endow this part of the sky with some of the brightest of her luminaries.  The brightest star in the sky, Sirius, is easily found trailing behind Orio as he gracefully wheels across the meridian.  To the astronomers of the 17th Century who depicted the constellations in the first star atlases Sirius represented a gleaming jewel in the collar of Canis Major, one of Orion’s two hunting dogs.  Its name is derived from the Greek word for “scorching”, and when it was observed rising just before the Sun its light was thought to amplify the Sun’s rays, causing the “dog days” of summer.  Long before the Greeks the ancient Egyptians noticed that this “heliacal rise” corresponded with the annual life-giving flood of the Nile river.  They saw it as the embodiment of the soul of Isis, one of their principal deities and watched for its first appearance each year for three millennia.  Sirius gets its dazzle from its relative proximity to us, located a scant 8.6 light-years away.  Only six star systems are closer to Earth, and only one, Alpha Centauri, can be seen with the naked eye.  

You can still glimpse the elusive planet Mercury low in the southwest as evening twilight falls.  The fleet planet reaches his greatest elongation east of the Sun on the evening of the 24th.  You should be able to spot him by around 6:00 pm local time, when he will be a bit over five degrees above the horizon.  Viewing him is a feat that, legend has it, that the great astronomer Nicholas Copernicus never achieved.  Despite this detail, he correctly placed Mercury as the innermost planet in his epic work, “De Revolutionibus Orbium Coelestium”.

Mars is steadily moving eastward among the stars of Aires, the Ram.  Early this week he floats just north of the more distant planet Uranus.  To spot this distant “ice giant” planet look at Mars with a pair of binoculars.  Uranus will appear as the brightest of the faint stars below Mars’ ruddy glow.  Point a small telescope at this “star” and you will see a tiny greenish disc that’s some 2.9 billion kilometers (1.8 billion miles) away.  The two planets will appear closest together from the 19th through the 22nd.

  The Sky This Week

The Sky This Week, 2021 January 12 - 19

The Moon, imaged from Alexandria, Virginia on 2020 March 2, 02:51 UT.
The Moon, imaged from Alexandria, Virginia on 2020 March 2, 02:51 UT
with an Explore Scientific AR102 10.2-cm (4-inch) f/6.5 refractor and a ZWO ASI224MC color imager.

The Moon returns to the evening sky this week, with New Moon occurring on the 13th at midnight, Eastern Standard Time.  On the evening of the 14th you can spot her slender crescent low in the southwest during evening twilight.  Look for the elusive planet Mercury about two degrees to the right of Luna’s crescent that evening.  As the week progresses the Moon climbs higher in the evening sky, drawing a bead on ruddy Mars.

The waxing crescent Moon offers fine views for owners of small telescopes.  Judging from the back-ordered inventories of popular telescope vendors it looks as if many people received telescopes as gifts during the holiday season, and Luna is a great target for first-time telescope owners.  I often say that the Moon is “looked over, then overlooked”, but spending time exploring her many varied surface features can be a wonderful retreat from the constant barrage of the 24-hour news cycle.  As our closest neighbor in space even small instruments will show an abundance of detail, and it helps to have an atlas of the Moon handy for your exploration.  There are many of these available online.  The Moon’s larger features bear names that were for the most part assigned long ago by the first astronomers to gaze on her with crude telescopes.  Her darker areas are known as “seas” (“maria” in Latin), “lakes” (“lacus”), “bays” (“sinus”), etc. and bear names like Mare Imbrium (Sea of Rains) and Sinus Iridum (Bay of Rainbows).  These large-scale features are the remnants of collisions with large asteroids early in the history of the solar system’s formation.  Individual smaller craters are named after famous people from classical astronomical literature as well as more modern contributors to lunar science.  Each successive night reveals new features along the “terminator” which is the sunrise/sunset line that creeps slowly eastward from our point of view.  The low Sun angle along the terminator throws features into stunning relief as ink-black shadows give way to dazzling sunlit terrain.  A 3- or 4-inch aperture telescope will show many hundreds of features and terrain textures.  Spend some time taking good long looks at our fair neighbor and you’ll want to return each month.

As the Moon moves farther along the ecliptic her light begins to wash out the faint stars that characterize the late autumnal constellations.  To challenge her, the bright stars of winter roll into the evening hours, offering more treats for the novice telescope user.  By the late evening the bright constellation of Orion, the Hunter is well up, dominating the southern sky.  Surrounding him is a large circle (or hexagon) of bright stars.  Point your telescope at these luminaries and you will see their colors, ranging from the icy blue of Sirius, the brightest star in the night, to the golden yellow of Capella, northernmost of the circle’s stars, to the red-tinted Aldebaran, the “eye” of Taurus, the Bull, and Betelgeuse, the left-hand “shoulder” of the Hunter himself.  Now sight in on Castor, the fainter of the two Gemini “twin stars” to the northeast of Orion.  Your telescope will reveal two stars tucked close together.  Each of these stars is itself a binary star, as is a fainter companion nearby, thus making Castor a six-star system!

As mentioned earlier, the planet Mercury is now putting in an appearance in the evening twilight sky.  Mercury never strays very far from the Sun, so he’s almost never visible against a dark sky.  This week, though, he advances eastward from the Sun’s glare for one of his better evening apparitions for the year.  The Moon will help you find him at dusk on the 14th, and each night for the next week or so you should look in the same general part of the sky for his glow.  

Mars continues his eastward trek through the late autumn stars.  He is still easy to spot despite his fading light.  He is now some 10 times fainter than he was at opposition, but his red hue and lack of nearby bright stars should make him easy to pick out.  Through the telescope you’ll see a tiny gibbous pink disc.

Venus is now becoming a challenge to early-rising skywatchers.  She now rises in gathering twilight an hour before the Sun.  You will need a flat eastern horizon to catch her before she is overwhelmed by the pending sunrise.

  The Sky This Week

The Sky This Week, 2021 January 5 - 12

The Full Cold Moon rising, Ocean City, Maryland, 2020 December 29.
The Full Cold Moon (and Orion) rising, Ocean City, Maryland, 2020 December 29
HDR image made with a Canon EOS Rebel SL2 DSLR and EF-S 18-55mm zoom lens @ 18mm, f/8.

The new year finds the Moon waning in the morning sky, coursing her way through the rising constellations of spring.  Last Quarter occurs on the 6th at 4:37 am Eastern Standard Time.  You’ll find Luna to the northwest of the bright star Spica before dawn on the 6th.  By the week’s end she is low in the southeastern sky, passing through the first of the rising summer constellations.

Earth reached perihelion, its closest point to the Sun, on January 2nd.  Fortunately for us our planet’s yearly excursion around our star follows a nearly circular path that varies only 5 million kilometers (3 million miles) between apsides.  The eccentricity of Earth’s orbit varies over periods of hundreds of thousands of years due to the gravitational influence of the other planets in the solar system.  Currently it is trending toward a more circular state, reaching a minimum in about 28,000 years.   

We are now at the point in the year where we are seeing the latest sunrises in the Northern Hemisphere.  Here in Washington Old Sol crests the horizon at 7:27 am EST.  By the end of the week he will rise one minute earlier.  However, the time of sunset is now just after 5:00 pm and we have added five minutes of total daylight since the winter solstice.  The longest nights of the year are now safely in the rear-view mirror.

The splendor of our winter constellations is best appreciated during the month of January.  The stars that comprise the “Great Winter Circle” dominate the evening hours, led by the striding figure of Orion, the Hunter.  No other constellation boasts as many bright and colorful stars as this one which is visible from every inhabited part of the globe.  Anyone who has done any casual stargazing on a winter night has probably noticed the three perfectly aligned stars that make up Orion’s “Belt” framed by the first-magnitude stars Betelgeuse to the northeast and Rigel to the southwest.  All of these stars are easily visible from urban environments, but it is the view from more rural sites that really brings out the splendor of the constellation.  From a dark site the first thing you will notice are the colors of the principal stars.  Betelgeuse shines with a ruddy tinge while Rigel and the Belt Stars sport an icy blue hue.  These colors tell us something about the nature of these stars.  Betelgeuse is relatively cool while its companions are very hot.  All of these stars shine across enormous gulfs of space, ranging from about 550 light-years for Betelgeuse to 2000 light-years for Alnilam, the middle star in the “Belt”.  The latter is one of the most intrinsically bright stars in our galaxy, with some 500,000 times the luminosity of our little Sun.

As midnight falls another brilliant blue star lies on the meridian at the end of a southeasterly line from Orion’s belt.  This is Sirius, the brightest star in the entire sky and chief luminary of Canis Major, the Greater Dog.  Unlike Orion’s powerhouses, Sirius is bright by dint of its proximity, just 8.6 light-years away and a luminosity of 25 Suns.  Both Sirius and Orion figure prominently in the sky lore of many ancient civilizations and led to humanity’s first reckonings of time.  

Another planetary gathering takes place in the southeastern sky at dusk this week when Mercury, Jupiter, and Saturn convene in the early twilight.  From the 9th to the 11th the three planets will be within three degrees of each other, but they will only be a few degrees above the horizon at 5:30 pm local time.  You will need a very clear sky, an unobstructed horizon, and binoculars to easily see them.

Mars is now the sole planet that’s easily visible during the evening hours.  You will find his ruddy glow on the meridian at 7:00 pm as he makes his way from the bounds of Pisces into the diminutive constellation of Aires, the Ram.  Mars appears slightly brighter than Betelgeuse in Orion, but the two objects share a warm reddish tint.  Mars now shows a small gibbous-phase disc in the telescope eyepiece.

You can still spot bright Venus low in the southeast half an hour before sunrise.  Look for a very slender crescent Moon near her before dawn on the 11th.

  The Sky This Week

The Sky This Week, 2020 December 23 - 2021 January 5

Great Conjunction + 1 day, imaged at the U.S. Naval Observatory, 2020 December 22.
Great Conjunction + 1 day, imaged at the U.S. Naval Observatory, 2020 December 22
with a Canon EOS Rebel SL2 DSLR and USNO's 30.5-cm (12-inch) f/15 Clark/Saegmüller refractor.

‘Tis the Night Before Christmas and up in the dome
We eagerly wait for the nightfall to come.
The slit has been opened, the lens cap’s been stowed
The night sky awaits like a wide-open road.

The solstice just passed on the 21st day,
The Sun’s southernmost point on his orbital way.
The year’s longest nights are upon us right now
But they start to get longer when the Yule log’s aglow.

The Moon is now waxing through autumnal stars
Her gibbous begins the week passing by Mars.
Full Moon occurs on the 29th hence,
Then wanes among spring’s stars as the New Year commences.

Jupiter shines in eve twilight’s last glow,
With much fainter Saturn behind him in tow.
The pair were quite close when the solstice occurred,
Old Jove moving eastward will get the last word.

Red Mars dashes quickly through Pisces’ faint lights,
His ruddy glow fading as he recedes in the night.
He’ll be with us well into summer next year,
By August he finally will disappear.

The Great Winter Circle shines high in the night
With bright stars a-twinkling with all of their might.
Their colors add contrast to enhance the dark sky
While far down below they’re a treat for the eye.

Orion is now rising high up in the east,
Shield raised in defiance of Taurus the beast.
The Great Winter Circle surrounds his bold shape, 
While faithful dog Canis leaps up in his wake.

Late night brings Sirius, the Dog Star on high,
By New Year’s he transits as midnight draws nigh.
The brightest of stars warm the long winter’s night,
His colorful cohorts all add to the sight.

Ten of the brightest of stars in the sky, 
Light these long nights of winter as Old Sol plays shy.
With the solstice now past us we’ll all soon be glad,
For the days getting longer than the ones we’ve just had.

The first stars of summer rise just before dawn
With dazzling Venus soon tagging along.
The planet’s bright glimmer shines in the southeast
As brightening twilight snuffs the bright stars to sleep.

So Peace to your families, neighbors, and friends,
We wish you the best that the holiday sends.
The stars mark the comings and goings of time,
So stop to enjoy them, and so ends my rhyme.

Happy Holidays from all of us at the U.S. Naval Observatory!

And my most sincere apologies to Clement Clark Moore.


  The Sky This Week

The Sky This Week, 2020 December 15 - 21

Orion (with faded Betelgeuse), imaged 2020 January 1 from Mollusk, Virginia.
Orion (with faded Betelgeuse), imaged 2020 January 1 from Mollusk, Virginia
captured with a Canon EOS Rebel SL2 DSLR on an Omegon MiniTrack LX2 mechanical star tracker

The Moon returns to the evening sky this week, waxing to First Quarter on the 21st at 6:41 pm Eastern Standard Time.  Look for Luna’s slender crescent low in the southwest near the close pairing of Jupiter and Saturn in the twilight hours of the 16th and 17th.  By the end of the week you will find her approaching ruddy Mars. 

The 21st also marks the date of the winter solstice, which will occur at 5:02 am EST.  This is the moment when the center of the Sun’s disc reaches an ecliptic longitude of 270 degrees relative to the center of the Earth.  In more practical terms it is also the day when the Sun reaches its most southerly point along the ecliptic, providing Northern Hemisphere residents with the shortest day of the year.  Here in Washington, DC that corresponds to 9 hours 26 minutes of daylight.  At the time of the solstice Old Sol will be directly overhead about 250 kilometers (150 miles) north of Pretoria, South Africa.

Yet another event occurs on the 21st this year in the form of a sight last seen by people in the year 1226 CE.  This will be the extraordinarily close pairing of the planets Jupiter and Saturn that will play out in the evening twilight sky.  If you’ve been watching the two planets over the course of the past few months you have seen Jupiter slowly but surely inch up on Saturn, and on the 21st they will pass just six arcminutes apart from each other.  While they won’t appear to merge together as seen with the unaided eye, that apparent distance is about one-fifth the apparent diameter of the Moon.  They will produce a spectacular view in the low-power field of a telescope, especially as the sky darkens and their respective flocks of moons become visible.  These two planets generally encounter each other about every 19.8 years, and when they meet it is often called a “Great Conjunction”.  After 19 of these encounters, their 20th can be very close, as is the case here.  They were actually a tad closer in 1623, but that conjunction took place on the far side of the Sun and so was not visible.  The 1226 close conjunction, which occurred on March 5th, brought the two planets to within three arcminutes of each other in a dark sky, which must have caused great consternation to astrologers of the day.  The next close encounter of the two gas giants will occur after 19 more Great Conjunctions.  On August 24, 2417 they will once again pass very close to each other, just five arcminutes apart.  Mark your calendars!

The long winter nights may be dark, but Mother Nature has seen fit to do her part to brighten the view.  By the late evening the spectacular constellations of the Great Winter Circle are marching toward the meridian, led by perhaps the most splendid of all, Orion, the Hunter.  Within the bounds of the circle you will find ten of the 30 brightest stars in the sky, four of which reside in Orion.  You may recall that last year one of Orion’s stars lost much of its luster; Betelgeuse, the red-tinged star marking one of the Hunter’s shoulders, faded to about the same brightness as the three “Belt Stars”.  Happily the star has returned to its former brightness this year, but astronomers are still baffled by its deep minimum.

A somewhat brighter red-hued object now dominates the early evening hours.  Mars crosses the meridian at around 7:30 pm local time, set like a glowing coal among the faint stars of Pisces.  Although he has lost much of the luster he had at opposition in early October, he still has the ability to get your attention.  The distance between Earth and Mars is rapidly increasing now, and his apparent disc is now just half the size that it was back then.  You will need at least a six-inch telescope to see details on his distant surface.  

Venus is gradually dropping toward the Sun in morning twilight.  She rises at around 5:30 am, just before the onset of morning twilight.  Look for her bright glow in the southeastern sky about half an hour before sunrise.

  The Sky This Week

The Sky This Week, 2020 December 8 - 15

The Milky Way in Perseus and Cassiopeia, imaged 2019 September 28 from Blackwater Falls State Park, Davis, West Virginia.
The Milky Way in Perseus and Cassiopeia, imaged 2019 September 28
from Blackwater Falls State Park, Davis, West Virginia
captured with a Canon EOS Rebel SL2 DSLR

The Moon wanes in the morning skies this week, moving southward along the ecliptic as she passes through spring’s rising constellations.  New Moon occurs on the 14th at 11:17 am Eastern Standard Time.  Those who happen to be located in southern Chile and Argentina will be treated to a total solar eclipse at that time.  For 2 minutes and 10 seconds the Sun’s face will be completely obscured by the Moon in one of Nature’s most spectacular sights.  Can’t get to Patagonia by next week?  Not a major problem.  You’ll only need to wait until April 8th, 2024 for a 4.5-minute eclipse that crosses the U.S. from Texas to the Great Lakes and northern New England.

Another of Nature’s spectacles is gearing up for a splendid viewing opportunity over the weekend.  The annual Geminid meteor shower will peak on the night of December 13-14, and there will be no moonlight to interfere with the view.  This is one of the most consistent showers from year to year, with up to 100 meteors visible per hour from dark locations.  The shower members appear to radiate from a point in the sky near the bright star Castor in the constellation of Gemini, and unlike many meteor showers the radiant is well above the horizon in the evening hours.  By 10:00 pm local time the radiant is about 40 degrees above the horizon, and it is almost directly overhead at 2:00 am.  Geminids are characterized by relatively slow, bright meteors that can be vividly colored.  Unlike summer’s Perseids, these slower meteors don’t tend to leave persistent smoke trains behind them.  While almost all of the year’s periodic showers are produced by the passage of comets through the inner solar system, the Geminids are the spawn of an asteroid, (3200) Phaethon.  Discovered in 1983, this was the first asteroid to be found by a space-based instrument, and it has the distinction of having the closest perihelion distance of any named asteroid.  It is now thought to be a defunct comet nucleus, sputtering off material as it orbits the Sun every 1.43 years.

This is the final week in 2020 to participate in the Globe at Night citizen-science sky awareness program.  From now until December 15th you are encouraged to go outside, look up, and count stars.  This month’s featured constellation is Perseus, the Hero, which may be found high in the northeastern sky in the mid-evening hours.  Perseus lies just west of a line that connects the bright yellow-hued star Capella with the W-shaped asterism formed by Cassiopeia.  Look for a grouping of stars that resemble a wish-bone with the bright star Mirfak at the intersection of the wish-bone’s tines.  To make an observation, simply visit the web app on the Globe at Night website and compare your view of Perseus with the charts on the site.  The site’s sponsors are hoping to collect a total of 30,000 observer reports for the year.

The second-brightest star in Perseus is usually Algol, which is normally a second-magnitude object.  However, every 2.8 days the star fades to magnitude 3.4.  It is the prototype of a class of variable stars known as eclipsing binaries in which a brighter star is periodically eclipsed by a darker companion.  Its variability was first documented by Medieval Persian astronomers who named it “Al Ra’s al Ghul”, the Demon’s Head.  The demon it represented was the Gorgon Medusa in Greek mythology, a creature who had snakes for hair and the ability to turn people to stone if they looked into her eyes.  The clever Perseus was able to kill Medusa by looking at her reflection in his polished bronze shield before lopping off her head, which the Hero subsequently carried around with him as a grisly trophy.  This week Algol reaches one of its minima on the evening of the 8th at 9:38 pm EST.  Five hours later it will have regained its regular brightness.

Bright Jupiter continues to inch up on Saturn during evening twilight into the first hour of darkness.  You can easily spot Jupiter in the southwest shortly after sunset, and Saturn should appear shortly thereafter.  Jupiter will pass Saturn in two weeks in what is often called a “Great Conjunction” since it only occurs every 19.76 years.  This particular one will be truly memorable as the two objects will appear extremely close together on the evening of the 21st.  The last time they appeared this close together and were easily visible was the year 1226 CE!

Mars continues to shine through the night, but his brightness is gradually fading.  Fortunately he is located in a part of the sky that is bereft of bright stars, so he stands out despite his waning glory.  You can also identify him by his strong ruddy tint, unmatched by any other object in the sky.  If you have been following him through the telescope since his close opposition two months ago you will see that his disc is now almost half as big as it appeared at that time.  

Bright Venus can be spotted in the gathering morning twilight as she moves through the stars of the constellation of Libra.  She gets a visit from the waning crescent Moon on the mornings of the 12th and 13th.

  The Sky This Week

The Sky This Week, 2020 December 1 - 8

The Full Beaver Moon and Halo, imaged 2020 November 29 from Alexandria, Virginia.
The Full Beaver Moon and Halo, imaged 2020 November 29 from Alexandria, Virginia
HDR image captured with a Canon EOS Rebel SL2 DSLR

The Moon begins the week high above the rising stars of the Great Winter Circle, then wends her way into the morning sky as she wanes to Last Quarter, which will occur on the 7th at 7:37 pm Eastern Standard Time.  By the end of the week pre-dawn skywatchers can see her among the rising stars of the springtime constellations.

December 1st is generally considered to be the start of climatological winter, and all month long the Sun plays out a series of extremes centered on the winter solstice.  From now until December 11th we will experience the earliest sunsets of the year.  Here in the Washington, DC area that means that Old Sol slips below the horizon at 4:46 pm EST.  After the 11th he will gradually begin to set a tad later each day, and by Christmas he’ll set at 4:52 pm.  However, the time of sunrise is still creeping later each morning and won’t reach its latest time until the year’s end.  Fromm December 30th until January 10th sunrise in DC will be at 7:27 am.  The dates of these extremes are bisected by the solstice itself, which falls on the 21st.  This will be the shortest day of the year in the Northern Hemisphere.  In Washington we will see only 9 hours 36 minutes of daylight on that date.

This seemingly lopsided swing in the dates of solstice phenomena is a reflection on our desire to keep precise time.  If you were to measure time with a sundial, the dates of latest sunrise and earliest sunset would correspond to the solstice.  For centuries this scheme was adequate, but as mechanical timepieces became more precise it became apparent that the time kept by the Sun varied in its uniformity throughout the year.  Since the Earth travels on an elliptical orbit around Old Sol its orbital velocity changes, moving faster at perihelion and slower at aphelion.  However, its speed of rotation remains essentially constant throughout the year.  The time of “noon” as measured by a sundial occurs when the Sun crosses the sundial’s meridian, so as far as the sundial is concerned noon is always 12 o’clock.  However, bring a clock of constant rate into the mix and you’ll discover that the apparent time of the Sun’s noon meridian transit is not precisely every 24 hours.  Depending on the time of year the apparent noon transit of the Sun can be as much as 16 minutes ahead of or 14 minutes behind “clock time”, and the most rapid excursion between these points happens to occur between early November and mid-February, skewing the “clock times” of latest sunrise and earliest sunset.  A similar effect occurs around the time if the summer solstice, but its amplitude is about half of what it is in the winter.  The annual variation between apparent solar (i.e. sundial) time and clock time is known as the “equation of time”, and its graphical solution may be found in the form of the “figure 8” diagram that’s usually printed on Earth globes and maps in the middle of the Pacific Ocean.  This figure is called the “analemma”, and provides you with a handy guide to correct your sundial to the proper clock time…at least for a while.  The Earth is gradually slowing in its rotation, and the eccentricity of its orbit and its axial tilt are slowly changing as well.  Eventually we’ll have to redraw the analemmas on our globes.

Early evening skywatchers can still catch Jupiter and Saturn in the southeastern sky as evening twilight settles over the landscape.  Both planets are gradually losing ground to the Sun, setting about three minutes earlier each passing night.  Jupiter has a slight advantage, though, as you can see by watching him inch closer to Saturn over the next few weeks

Mars is now the planet that will get your attention each night.  He crosses the meridian shortly after 8:00 pm local time, and his pink tint distinguishes him from all other bright objects in the sky.  He continues to fade gradually as the distance between him and Earth increases, and the telescope will show that his disc is shrinking rapidly as well.  Details on his distant surface are becoming harder to see as he recedes from us, and the recent development of one of his infamous dust storms further hinders the view.

You can still find bright Venus in the pre-dawn sky, but she, too, is gradually inching closer to the glare of the Sun.  Look for her in the southeastern sky in the gathering morning twilight.

  The Sky This Week

The Sky This Week, November 17 - 24

The Pleiades, imaged 2017 December 17 from Great Meadow, Virginia.
Messier 45, The Pleiades, imaged 2017 December 17 from Great Meadow, Virginia
with an Explore Scientific AR102 10.2-cm (4-inch) f/6.5 refractor and a Canon EOS Rebel T2i DSLR

"Many a night I saw the Pleiads, rising thro' the mellow shade,
Glitter like a swarm of fireflies tangled in a silver braid."
Alfred, Lord Tennyson - Locksley Hall

The Moon returns to the evening skies this week, waxing through her crescent phases as she climbs through the faint autumnal constellations.  First Quarter falls on the 21st at 11:45 pm Eastern Standard Time.  Luna starts the week near Jupiter and Saturn, appearing closest to the pair of planets on the evening of the 19th.  By the week’s end she will approach the ruddy glimmer of Mars.

If you have an unobstructed view of the northern horizon, this is the time of year when the familiar asterism known as the Big Dipper reaches its lowest point in the sky, scraping the tree-line in its endless journey around Polaris, the North Star.  The seven stars of the Dipper are the brightest members of the larger constellation of Ursa Major, the Great Bear.  Our present association of a bear with these stars has a long tradition dating back at least to classical Greek times, and it may possibly date back even further to folklore that developed in prehistory.  Many cultures in the Northern Hemisphere identify it as a bear, including many Native American peoples.  One of my favorite stories comes from the Iroquois people who inhabited much of the northeastern U.S. before Europeans arrived.  They saw the four stars of the “bowl” of the Big Dipper as a bear, while the three stars of the “handle” represented three hunters.  The hunter closest to the bear carried a bow and arrows, while the hunter at the end of the “handle” carried firewood.  The star we now call Mizar, which forms the bend in the “handle”, was a hunter who carried a pot, represented by the naked-eye companion to Mizar, the star Alcor.  Every year the hunters pursued the bear around the pole, and each autumn, as the bear neared the northern horizon, they caught it and cooked it in the pot.  The blood from the bear’s arrow wounds dripped down to Earth, staining the trees red and causing the leaves to fall.  The hunters, in turn, had a well-stocked larder for the coming winter.

Later in the evening, if you look to the east, you will find another star pattern associated with boreal winter.  While it is a very diminutive group that can barely be seen from the city, it stands out in the sky as you move to darker skies.  This group is the Pleiades, also known as the Seven Sisters in our Greco-Roman derived sky lore.  Ancient Chinese records dating to some 4500 years ago mention them, and recent work by archaeoastronomers has shown that many Mesoamerican cultures built their ceremonial centers to align with the Pleiades’ rising.  Virtually every culture that has left some record of their sky legends mentions the group, and they even appear in the lore of the fabled Middle Earth of J.R.R. Tolkien’s epic tales of hobbits, elves, and magic rings, where they were known as “Remmirath”, the “Netted Stars”.  In Japanese they are known as “Subaru”, and you can see a stylized representation of them on every car of that name.  They are often associated with the coming of winter in northern climes, and sailors regarded them as portents of gales and fierce seas.  Others associate them with agriculture, marking the time to plant when they set just after the Sun in the spring and time to reap when they appear in the fall.  

The Pleiades are a true star cluster, located about 440 light-years from Earth.  Its brightest members have a dazzling blue tint as seen in a telescope and under very dark conditions it is possible to see the remnants of the clouds that formed them some 100 million years ago.  Most of us can see six or seven stars with the unaided eye, but very keen-eyed people can see a dozen.  A small telescope will reveal about 80 members, while large telescopes have identified over 1000 stars in the cluster.

Jupiter and Saturn may still be glimpsed in the southwest as evening twilight fades to darkness.  They will get a visit from the Moon on the evenings of the 18th and 19th.  If you have been watching them for the past few weeks you’ve probably noticed that the gap between them is narrowing; Jupiter is gradually gaining ground on the ringed planet.  The gap will continue to close, and in a month we will see the closest appulse of these two planets since the year 1623.

Mars has resumed his eastward motion against the stars, but it will be a few more weeks before this becomes noticeable.  He still dominates the sky throughout the evening hours beaming down from among the faint stars of Pisces.  Although his disc is now shrinking, a modest telescope on a night of steady seeing will reveal his dusky surface features and small polar ice cap.  

You will find Venus in the pre-dawn sky without much difficulty.  Her bright glow remains visible right up to the time of sunrise.  If you look for her at around 5:30 am you should see her near the bright star Spica as the week begins.  She moves rapidly east from the star over the next several mornings.

  The Sky This Week

The Sky This Week, 2020 November 10 - 17

The Andromeda Galaxy, imaged 2018 October 7 from Mollusk, Virginia.
Messier 31, the Andromeda Galaxy, imaged 2018 October 7 from Mollusk, Virginia
with an Explore Scientific AR102 10.2-cm (4-inch) f/6.5 refractor and a Canon EOS Rebel T2i DSLR

The Moon may be found in her waning crescent phases before dawn as the week opens.  New Moon occurs on the 15th at 12:07 am Eastern Standard Time.  Look for Luna’s crescent about six degrees above dazzling Venus in the morning twilight of the 12th.  On the following morning the Moon is about halfway between Venus and her inner solar system companion Mercury.

Crisp late autumn nights with no Moon in the sky mean that it’s time for the November observing campaign for the citizen-science program Globe at Night.  This month’s target constellation is Pegasus, the mythical Flying Horse.  Its “landmark” feature is an almost perfect square made up of second-magnitude stars that transits the meridian at around 8:30 pm.  Pegasus is high in the sky for mid-northern observers, and I have always used it as a test for dark skies.  Within the square are a number of faint stars to help you judge the quality of your sky.  Urban and near-suburban skywatchers probably won’t see any stars within the bounds of the square, but as you venture further out into the country faint stars begin to fill it in.  If you can spot three or four stars in the square you are in a pretty dark locale, but observers in truly dark sites can spot nearly a dozen!  You can contribute your star count with the Globe at Night Web App, which gives you a very simple interface to report your findings.  So far this year the program has gathered over 26,000 reports, and the program’s goal is 28,000 by the end of the year.  The program aims to chart light pollution and its effects on both professional and amateur astronomers.

If you are in a place where you can see some of the faint stars in the square take a few moments to track down something that’s almost mind-boggling.  The upper left corner of the square is marked by the star Alpheratz, which is shared by Pegasus and the constellation of Andromeda.  If you allow your gaze to wander toward the “W” of Cassiopeia you will notice two diverging “chains” of stars that lead from Alpheratz.  Follow the lower, brighter chain to the second star, then draw an imaginary line to the second star in the upper, fainter chain.  Extend your gaze in the same direction for the same distance and you will notice a fuzzy patch of light that looks like a tiny detached portion of the Milky Way.  It is, in fact, another galaxy like our own, its faint light glimmering across 2.5 million light-years of intergalactic space.  Known as the Andromeda Galaxy, this is the most distant object that you can see with the unaided eye.  Its elongated shape becomes apparent in binoculars, and it stubbornly refuses to resolve into stars in virtually any amateur telescope.  Its light was described very aptly by the German astronomer Simon Marius in 1612 who remarked that it resembled “the light of a candle shining through horn”.  That light is the combined light of several hundred billion stars!

The Andromeda Galaxy and the Milky Way are the two largest members of the “Local Group” of galaxies, a loose grouping of a few dozen small systems under the sway of that larger ones.  The Andromeda Galaxy is moving toward us, and the mutual gravity of the two systems will bring them together in a slow-motion collision in about 4.5 billion years.

Back in our solar system, Jupiter and Saturn are struggling to stay ahead of the relentless Sun.  The two giant planets are still easy to spot in the southwest after sunset, but by the time that twilight ends they are dipping toward the horizon.  Jupiter will ultimately win the race, passing Saturn in a spectacular conjunction on the winter solstice.

Mars holds court in the evening sky, especially as Jupiter sinks into the trees.  The red planet is very hard to miss.  Not only is he bright, he sports a decidedly ruddy tint and has no competition from nearby bright objects.  However, his diminutive size means that as we earthlings recede from him he gets a bit fainter each passing night.  His apparent diameter is quickly shrinking as well.  That said, his disc won’t approach this size again until the year 2033.  

Venus continues to gradually inch toward the Sun in the pre-dawn sky.  She is still easy to see over the eastern horizon as twilight begins to gather.  The Moon will be in her vicinity on the mornings of the 12th and 13th.

Elusive Mercury also puts in an appearance just before sunrise.  He reaches greatest elongation from the Sun on the 10th, and you should be able to spot him about 10 degrees below Venus.  The best time to look for him will be the morning of the 13th, when the Moon is halfway between the two planets.

  The Sky This Week

The Sky This Week, 2020 November 3 - 10

The Perseus Double Cluster, imaged 2018 October 7 from Mollusk, Virginia.
The Perseus Double Cluster, imaged 2018 October 7 from Mollusk, Virginia
with an Explore Scientific AR102 10.2-cm (4-inch) f/6.5 refractor and a Canon EOS Rebel T2i DSLR

The first full week back on Standard Time finds the Moon cruising high on the ecliptic as she wends her way through the rising stars of the winter constellations.  Last Quarter occurs on the 8th at 8:46 am Eastern Standard Time.  Luna begins the week between the “horns” of Taurus, the Bull, then passes through the constellation of Gemini, the twins and the obscure stars of Cancer the Crab.  Early risers will find the Moon passing through the “head” of Leo, the Lion, mid-way between the bright star Regulus and the gold-hued glimmer of Algieba.

“Falling back” to Standard Time is usually a bit of a shock for me.  I enjoy being out under the stars, but usually not until after dinner.  Now the sky is dark when I sit down for my evening meal, and when I do head out with my telescope it’s as if an entire season has suddenly elapsed.  The three stars of the Summer Triangle, Vega, Deneb, and Altair, along with their attendant constellations, are now poised to set, leaving the barren autumn stars patterns to occupy the sky over my yard.  That said, I don’t have to wait too long before the bright stars of winter begin to rise.  One of my favorite sights is the figure of Orion seeming to climb over the horizon, ready to ward off the charge of nearby Taurus.  

High overhead is the diminutive W-shaped group of stars that form Cassiopeia.  This area of the sky is rife with an array of beautiful star clusters that glitter like tiny jewel boxes in the telescope eyepiece.  From a dark site you can see a fairly bright portion of the Milky Way behind the constellation’s main stars that trails off into the neighboring constellation Perseus.  This constellation has a shape that reminds me of the “winner’s portion” of a wishbone, with the bright star Mirfak at the wishbone’s center.  Embedded in the Milky Way between Perseus and Cassiopeia is one of the true treasures of the sky, the “Double Cluster”.

From a dark sky the Double Cluster appears as a fuzzy patch of light to the naked eye, but a pair of binoculars will begin to resolve its starry splendor.  My favorite view is through my 4-inch telescope at low magnification where the two star clusters can be seen in the context of the Milky Way background.  Each cluster resolves into hundreds of stars, and at a distance of some 7500 light years, the brighter members must be enormously luminous to appear as they do in the eyepiece.  Most of the bright stars are blue supergiants, which means that the clusters are quite young on the cosmic scale, forming just 10 to 15 million years ago.  Careful scrutiny will also show a smattering of red supergiant stars scattered between the two main clusters.  These stars are analogous to Betelgeuse in Orion, but they are over five times farther away.  

Shifting our gaze back to Perseus, another much closer star cluster surrounds the constellation’s brightest star, Mirfak.  This group, known as Melotte 20, is widely scattered and is best seen in binoculars.  It is about 510 light-years away. Ten of its members are visible to the naked eye, but binoculars will reveal dozens more.  Most of the stars, apart from Mirfak itself, have a pleasing blue tint.

Returning to Standard Time places Jupiter and Saturn into the early evening sky, and if you wait too long they will be gone for you.  Jupiter sets at around 9:30 pm with Saturn following a bit over 20 minutes later.  Your best views are still in evening twilight, so plan on a late dinner if you still want to see them at their best.

Mars actually benefits from the return to Standard Time.  The red planet crosses the meridian at around 10:00 pm, so you have the best part of the night to give him a look through the telescope.  Keen-eyed observers will note that he is already beginning to fade after his close opposition a few weeks ago, but his disc can still reveal tantalizing features to patient observers.  I enjoy looking at Mars since it is the only place in the solar system other than the Moon and Mercury where I’m looking at a solid surface.  

Venus remains visible before sunrise, glowing brightly among the stars of Virgo.  On the morning of the 5th she passes one degree south of the beautiful second-magnitude double star Porrima.  Closer to the horizon look for the first-magnitude star Spica.  Early in the week the glimmer of elusive Mercury may be seen a few degrees east of the star.

NASA Invites Media to Briefing on OSIRIS-REx Asteroid Sample Stowage
  Solar System News

NASA Invites Media to Briefing on OSIRIS-REx Asteroid Sample Stowage

NASA will host a media teleconference at 4 p.m. EDT today, Thursday, Oct. 29, to provide an update on the status of the agency’s Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer (OSIRIS-REx) spacecraft and the mission’s work to safely stow the sample it collected from asteroid Bennu.
NASA’s OSIRIS-REx Spacecraft Successfully Touches Asteroid
  Solar System News

NASA’s OSIRIS-REx Spacecraft Successfully Touches Asteroid

NASA’s Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer (OSIRIS-REx) spacecraft unfurled its robotic arm Tuesday, and in a first for the agency, briefly touched an asteroid to collect dust and pebbles from the surface for delivery to Earth in 2023.
Solar Cycle 25 Is Here. NASA, NOAA Scientists Explain What That Means
  Solar System News

Solar Cycle 25 Is Here. NASA, NOAA Scientists Explain What That Means

Solar Cycle 25 has begun. During a media event on Tuesday, experts from NASA and the National Oceanic and Atmospheric Administration (NOAA) discussed their analysis and predictions about the new solar cycle – and how the coming upswing in space weather will impact our lives and technology on Earth, as well as astronauts in space.

  The Sky This Week

The Sky This Week, 2020 August 25 - September 1

Sagittarius and the summer Milky Way, imaged from Smith's Ferry, Idaho, 2017 August 21.
Sagittarius and the summer Milky Way
imaged from Smith's Ferry, Idaho, 2017 August 21

The Moon skims the southern horizon this week, waxing toward her Full phase, which occurs on September 2nd at 1:22 am Eastern Daylight Time.  We usually call September’s Full Moon the Harvest Moon, but I have always thought that this name was best used on the Full Moon that occurs closest to the autumnal equinox.  That Full Moon will fall on October 1st, a time when farmers would be traditionally bringing in their harvested bounty.  Fortunately, some crops are at their peak ripeness now, so an early September Full Moon is often called the Corn Moon, Barley Moon, or Fruit Moon.  Luna passes just south of bright Jupiter on the evening of the 28th.  On the following night she will be just southeast of Saturn.

We are now approaching the time of year when we see the greatest rate of loss in the length of daylight.  Over the course of the week we will lose about 17 minutes of total daylight, with 10 minutes of that coming off our sunset times.  Since the time of the summer solstice more than an hour and a half of daylight has disappeared, and we’ll lose another hour by the time the equinox occurs.

The lengthening nights have a positive side, though, since we can now enjoy stargazing at more reasonable times.  The constant seasonal change of the constellations seems to slow a bit during the late summer and early autumn, giving us more time to take in the splendors of the summer sky.  Even with the brightening Moon moving through the evening sky we can still see the brighter summer constellations.  To the south, the curving arc of the stars of Scorpius hover over the southern horizon, led by the orange-tinted star Antares.  You will find three second-magnitude blue-tinted stars that mark the Scorpion’s “head” to the right of Antares.  The middle star of this trio is called Dschubba, and over the past few years it has shown remarkable variability.  Normally it is comparable to its northern and southern companions, but a couple of times over the past 20 years it has doubled in brightness, second only to Antares as the constellation’s brightest star.  North of Dschubba is the star Acrab, which resolves into a fine double star in small telescopes.  However, there is more than meets the eye here, as each component is itself a triple-star system.  I often wonder what it might be like to live on a planet in orbit around such unusual star systems!

East of Scorpius is the constellation of Sagittarius, the Archer.  To the ancients this represented a Centaur, a mythical beast with the head and torso of a man and the body of a horse.  Here is one of those situations where I have trouble “seeing” what the ancients saw, but fortunately we can look at the constellation’s brighter stars and delineate a fairly respectable “teapot” asterism.  If you have a really clear view of the southern horizon you can even imagine tea being poured out of the teapot’s spout into the tail of Scorpius, which makes an acceptable tea mug!  On moonless nights look for “steam” emanating from the teapot’s spout; that’s the bright Sagittarius star cloud of the Milky Way.  Our Galaxy’s center is about 30,000 light-years off in that direction.

The bright planets Jupiter and Saturn follow Sagittarius across the southern sky.  Jupiter’s retrograde motion has brought the giant planet closer to the “handle” of the teapot, and if you look at Old Jove with a pair of binoculars you will find him under another asterism known as the “teaspoon”.  Jupiter now crosses the meridian at 10:00 pm local time, so he’s in prime viewing position during the evening hours.  Look for the planet’s famous Great Red Spot near the center of his disc on the evening of the 29th.  On the following night you can watch his innermost large moon Io transit his disc with its shadow following behind it.

Saturn is also in prime viewing position during the evening hours.  Detail on this planet is much more subtle than the prominent cloud belts of Jupiter, but that is more than made up for by the planet’s enigmatic ring system.  Thanks to the multi-year observations of the Cassini space probe we now know that the rings are composed of a myriad of chunks of ice that form the flattest structure known in the solar system.  While they span hundreds of thousands of kilometers in diameter, they are less than 100 meters thick!

Mars continues to drift through the faint stars of Pisces and is still best placed for viewing in the wee hours of the morning.  He’s slowing his eastward pace as Earth catches up to him, and he will begin retrograde motion in another two weeks.  He is well within range of modest amateur telescopes, so if you’re up before dawn consider giving him a look.

Venus joins the rising stars of winter, beaming down from a northeasterly perch as morning twilight begins.  This week you will find her plodding eastward between the stars Castor and Pollux in Gemini and the star Procyon in Canis Minor.

  The Sky This Week

The Sky This Week, 2020 August 18 - 25

Scorpius and the summer Milky Way, imaged from Mollusk, Virginia, 2020 July 26.
Scorpius and the summer Milky Wa7
imaged from Mollusk, Virginia, 2020 July 26

The Moon returns to the evening sky this week, waxing through her crescent phases to First Quarter, which occurs on the 25th at 1:58 pm Eastern Daylight Time.  As she dives southward along the ecliptic, you will find her just over five degrees north of the bright star Spica on the evening of the 22nd.  She ends the week among the stars that form the “head” of Scorpius, the Scorpion.

For those of you who like stargazing in the evening sky, you may have noticed that sunset here in the Washington area now occurs before 8:00 pm.  That’s about 40 minutes earlier than the time of sunset at the summer solstice.  This means that for many of us in urban and suburban locations we can enjoy dark (ish) skies at around 9:00 pm.  If you’re in a darker location the sky is fully dark by around 9:30 pm.  We are currently losing about 2.5 minutes of daylight per day, so it’s becoming easier to enjoy your summer favorites and still get to bed at a decent hour.

Speaking of Scorpius, you will find this signature summer constellation crossing the meridian at 9:00 pm local time.  While it is placed in the southernmost reaches of our Washington skyline it is still one of the showpieces of the sky.  If you can find a spot to see it in all of its splendor you won’t need a lot of imagination to understand how it got its name.  Scorpius is a very ancient constellation, depicted in records of ancient Egypt and Mesopotamia that date back well over 5000 years.  It is led by a prominent red-hued star known as Antares, which translates as “rival of Mars”.  Antares is a red supergiant star, a highly evolved example of a star that is nearing the final stages of its life.  Like its counterpart Betelgeuse in Orion, Antares is vast, with a girth that spans hundreds of millions of kilometers.  If Antares occupied our Sun’s place in the solar system, the orbit of Mars would be inside of it!  Scorpius shares some other details with Orion as well.  Many of its stars are hot blue giant stars that share a common origin, much like the bright blue stars in Orion.  While the two constellations share similar physical characteristics, their mythology is also linked, but in an unusual way: you will never see the two in the sky together at the same time.  

Our Greco-Roman skylore tradition paints Orion as a boastful hunter who claimed that he could kill all the animals on Earth.  His pride and arrogance didn’t sit well with Gaia, goddess of the Earth, so she sent a scorpion to teach the hunter a lesson.  The scorpion’s powerful sting dispatched Orion, but he was saved “in the nick of time” by Ophiuchus, the Serpent-bearer, whose large constellation appears above Scorpius in our summer sky.  To appease both parties Zeus placed both Orion and the scorpion in the sky, but opposite each other so that they would never have to face off again.

Early in the week you can still see the bright stars-clouds of the Milky Way from dark-sky locations.  They rise up from the vicinity of Scorpius and arc overhead through the bright stars of the Summer Triangle.  Mild summer evenings make them particularly attractive to scan with binoculars or small telescopes.  The sheer number of stars that you can see is mind-boggling.  Also note the dark, seemingly empty regions of the Milky Way’s band.  These are clouds of non-luminous gas and dust that feed the formation of stars along the Galaxy’s plane.

Jupiter now shines brightly in the southeastern sky as soon as evening twilight starts to fall.  Old Jove is now in prime viewing position for evening stargazers, offering a variety of sights for the small telescope owner.  His constantly shifting bright moons and changing atmosphere can be studied with telescopes of four-inch aperture or larger.  On the evening of the 23rd you can watch his innermost moon Io drag its shadow across the planet’s disc, and on the following evening you can get a fine glimpse of the famous Great Red Spot rotating across his face.

Saturn should be your next stop after Jupiter.  I have been looking at this planet for decades through dozens of different telescopes and I still get a chill when I view it.  There is something about the view of Saturn that defines “other-worldly” and keeps me at the eyepiece.  One glimpse for yourself and I think you’ll see why.

Ruddy Mars waits in the wings, now rising at around 10:30 pm.  That’s still a bit late for me, but with later times of sunrise it’s now not unreasonable to take a look at the red planet in morning twilight.  He is steadily brightening and his visible disc is steadily growing as we near opposition, set for early October.

Venus accompanies Orion and the other rising winter constellations as morning twilight brightens the sky.  You should have no trouble spotting her beaming down from the stars of Gemini.


  The Sky This Week

The Sky This Week, 2020 August 11 - 18

Jupiter & Saturn, imaged from the U.S. Naval Observatory, Washington, DC, 2020 August 11.
Jupiter & Saturn, imaged from the U.S. Naval Observatory, Washington, DC, 2020 August 11
with the 30.5-cm (12-inch) f/15 Clark/Saegmüller refractor.

The Moon wanes in the pre-dawn sky this week, making her way through the rising winter constellations as the first light of dawn begins to brighten the eastern horizon.  New Moon occurs on the 18th at 10:42 pm Eastern Daylight Time.  You will find Luna just north of the bright star Aldebaran in Taurus, the Bull, on the morning of the 13th.  Luna will be close to dazzling Venus before dawn on the 15th.

As we mentioned last week, the annual Perseids meteor shower peaks on the nights of the 11th-12th and 12th-13th.  However, these aren’t the only nights to see members of this famous shower.  Activity from the Perseids will continue through the end of the month, and the shower will maintain about a quarter of its peak strength until late in the week.  Moonlight becomes less of a factor as the week passes, so if conditions aren’t great for viewing on the peak nights you can still see a decent show for a while longer.

The absence of the Moon means that it is time for the August campaign for the Globe at Night citizen-science program.  So far this year the program has recorded over 20 thousand observations from all around the world to help scientists understand the impacts of light pollution on a global scale.  The program started as a project initiated during the International Year of Astronomy in 2009 and has been going strong ever since.  This month the featured constellation is Cygnus, the Swan, whose brightest star, Deneb, is one of the apexes in the Summer Triangle asterism.  Deneb is the faintest and most northerly of the Triangle’s stars, but it can be easily seen even from the most urban locations.  The rest of Cygnus extends toward the middle of the Summer Triangle, with the Swan’s head, Albireo, nearly at its center.  This star is one of my favorite targets for small telescopes; it is an easily split double star with blue and gold components which I like to call the “Navy star”.  Between Albireo and Deneb lie the other stars in the constellation.  Suburban skywatchers should be able to see a cross-shaped grouping of stars that, with a little imagination, can be seen as a swan in flight.  Pick a clear night to find Cygnus, then go to the Globe at Night Web App to record your observation.

From a dark location you should be able to see Cygnus in all its splendor.  The swan seems to be “flying” along the path of the Milky Way, which seems to cleave into two parts along its path.  This feature continues down to the horizon and is known as the Great Rift.  While it has the appearance of being somewhat devoid of stars, it is actually an enormous cloud of cold, non-luminous gas and dust blocking the light from even more distant star clouds in our galaxy’s spiral arms.  These dark clouds are a feature of the summer Milky Way, and they continue along the parts of the galaxy that can only be seen from more southerly climes.  Indeed, the ancient Inca people and their relatives created much of their sky lore from the shapes of these dark features in the soft glow of the southern Milky Way.  We northerners only get to see a small part of them.

I finally had my first really good evening for observing Jupiter.  Due to its extreme southern declination it is very hard to see from my house during the brief time that he passes between my neighbor’s chimney and a large tree.  Almost invariably the time when Old Jove is in the right place a cloud scurries in front of him.  Such is the lot of the suburban astronomer.  However, I was able to have a nice session with Jupiter using the Observatory’s 125-year-old 12-inch refractor, whose old glass still provides great views.  The famous Great Red Spot was prominently featured, and the moon Europa was leading its shadow across the disc.  You don’t need a big telescope to enjoy these features, though; a good four-inch scope should show these features quite nicely.

Saturn was next on my agenda after Jupiter.  I can honestly say that even after decades of looking at the ringed planet through dozens of different telescopes there is still a certain sense of awe whenever I train the 12-inch on it.  Yes, occasionally I will lapse into a state of disbelief that such an amazing sight appears in Nature.

I’m looking forward to the views of Mars that I’ll get this fall, but even now the red planet beckons.  Mars now rises just before 11:00 pm, and you will have no trouble picking him out of the sparse stars of Autumn during the late night and early morning hours.  Modest telescopes will show many of his enigmatic surface features and dazzling polar ice cap.  Other than the Moon and Mercury, Mars is the only pother place in the solar system where you are looking at a solid surface.

Venus gets a pre-dawn visit from the Moon on the morning of the 15th.  She is now moving through the heart of the rising Great Winter Circle, drifting among the stars of Gemini. 

  The Sky This Week

The Sky This Week, 2020 August 4 - 11

The Summer Milky Way, imaged 2020 July 26 from Mollusk, Virginia.
The Summer Milky Way, imaged 2020 July 26 from Mollusk, Virginia
with a Canon EOS Rebel SL2 DSLR, 18mm @ f/5.6, composite of 12 90-second exposures at ISO 3200.

The Moon climbs northward along the ecliptic in the morning skies this week, passing through the rising autumnal constellations.  Last Quarter occurs on the 11th at 12:45 pm Eastern Daylight Time.  Early risers on the morning of the 9th get a nice treat as Luna poses just one degree south of the brightening planet Mars. 

August is the month to look for meteors.  In addition to an increase in the “background” count of random shooting stars, the annual Perseids meteor shower peaks at the end of the week.  This display is one of the most consistent from year to year, and shower members can be seen from mid-July through August.  This year the peak activity occurs on the nights of the 11th-12th and 12th-13th.  A single observer at a dark location may be able to see around 60 shooting stars per hour starting at around 11:00 pm local time when the radiant, in the constellation of Perseus, climbs into the northeastern sky.  The Perseids are particles that have streamed off of Periodic Comet 109/P Swift-Tuttle, which circles the Sun once every 133 years.  The comet was co-discovered in 1862 by Horace P. Tuttle, one of the most prolific American comet seekers, at Harvard College Observatory.  Tuttle had an interesting life and career, spending time at the U.S. Naval Observatory.  Each year in August Earth intersects the orbit of the comet, running headlong into the debris sputtered off its surface each time it rounds the Sun, causing the annual display.  Historical records indicate that the shower has been an ongoing event since at least the year 36 CE.  You’re best time to catch them will be between 11:00 pm and 1:00 am, when the waning Moon rises to brighten the sky.  The meteors are fast, flashing across the sky in mere seconds; the brightest ones leave persistent trains.

The waning Moon also means that it’s time once again to explore our home galaxy, the Milky Way.  From dark skies the luminous band becomes apparent by around 10:00 pm local time.  The densest part of the Milky Way is due south at this time, sandwiched between the stars of Scorpius and Sagittarius.  Unfortunately, many people have never seen this subtle sky glow, and on first encountering it they mistake it for a terrestrial cloud.  However, this cloud doesn’t move with respect to the stars, and it doesn’t take much optical aid to realize that it is comprised of uncountable numbers of stars.  A steadily held pair of binoculars is enough to start to resolve the brighter patches and dark lanes that snake through them.  Binoculars will also reveal that some of the brighter knots scattered among the star clouds are individual clusters of stars and glowing clouds of interstellar gas and dust.  One of my favorite sights of summer is a prominent star cluster located between the two stars that form the “stinger” of the Scorpion and the “spout” of the Teapot asterism of Sagittarius.  Known as Ptolemy’s Cluster or Messier 7, it is easily resolved in binoculars, and a small-aperture low-power telescope reveals a beautiful scattering of pale blue stars set against a background of millions of fainter ones.  Sweep up the Milky Way from this cluster and you’ll encounter a dozen similar treats!

Jupiter is prominent in the southeastern sky as twilight fades.  The giant planet crosses the meridian at around 11:30 pm, so you have plenty of time to get him focused in the telescope eyepiece.  Jupiter offers the largest apparent disc of any of the planets, and you should be able to see his dark equatorial cloud belts in telescopes of 3-inch aperture.  Almost any optical aid will reveal the planet’s four large Galilean moons, but a modest telescope will allow you to see their shadows cross the planet’s face.  On the evening of the 7th we get a shadow “two-fer”, with Ganymedes’ shadow on the disc until 9:53 pm EDT and Io’s umbra entering transit at 10:13 pm. 

Saturn follows Jupiter by about 10 degrees as they parade across the southern horizon.  While they appear close in the sky, they are actually very far apart.  Currently Old Jove is about 631 million kilometers (392 million miles) from Earth; Saturn is well over twice a far distant!  In fact, we don’t really see either planet in “real time” since the speed of light is finite.  Jupiter’s light takes 35 minutes to reach us, while Saturn’s glow takes just over 75 minutes!

Mars continues to brighten as he drifts through the stars of Pisces.  His eastward progress is beginning to slow as he approaches opposition in the fall.  He will spend the next few months in this general area of the sky, becoming very prominent by early October.  He will get a close visit from the Moon before dawn on the 9th.

Venus continues to drift eastward among the rising winter stars in the gathering morning twilight.  You should have no trouble spotting her in the east as she passes north of the prominent stars of Orion.