Archive for June, 2014

The Sky This Week , June 24 – July 1, 2014 !

The Sky This Week, 2014 June 24 – July 1

More musings on the Milky Way
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Scorpius, Sagittarius, and the galactic center, 2014 June 1
Imaged at Sky Meadows State Park, Paris, Virginia

The Moon returns to the evening sky this week following New Moon, which occurs on the 27th at 4:08 am Eastern Daylight Time.  Try to spot Luna’s slender day-old crescent six degrees to the south of bright Jupiter during evening twilight on the 28th.  On the evening of the 1st she’ll be located five degrees south of the bright star Regulus in Leo, the Lion.

The year’s latest sunset occurs on the 28th as the Sun sets at 8:38 pm EDT here in the Washington area.  Our earliest sunrise occurred back on the 14th, but Old Sol now rises about three minutes later than he did two weeks ago.  The time of sunset will gradually start to recede over the next couple of weeks, although most of us probably won’t notice the shortening days until well into the month of July. 

Despite the late sunsets, you still have most of the week to enjoy the spectacle of the summer Milky Way before the encroaching Moon begins to wash it out.  This band of amorphous light shows its most prominent sections to us during the summer months as the galaxy’s central regions wheel over the southern horizon.  The actual heart of the Milky Way is located some 30,000 light-years away in an area located just west of the tip of the “spout” of the teapot-shaped asterism formed by the brightest stars of Sagittarius.   The actual galactic center is hidden from our direct view by enormous clouds of stars and intervening dark molecular associations, but it is easy to see that the width of the ghostly band reaches its maximum in this direction.   Today, thanks to our ability to observe in multiple spectral bands, we know that the center of the Milky Way hosts a very compact but ultra-massive object: a “black hole” with a mass of several million Suns!  Fortunately for us, we’re located well away from the zone of intense X-ray and Gamma-ray radiation that this object occasionally unleashes when an unfortunate star passes too close, so we can enjoy the more benign denizens of our galactic neighborhood.  For this I suggest using binoculars on a good clear night.  If you start your viewing just to the right of the “Teapot” and work your way up the Milky Way toward the three bright stars of the Summer Triangle you’ll encounter many bright knots of star clusters and glowing clouds of diffuse gas.  All of these little gems are set against a background of a seemingly infinite number of stars.  But not quite infinite; the Milky Way is believed to contain about 200 billion stars, of which our little Sun is but one rather nondescript member.

We are now in the last couple of weeks of seeing bright Jupiter in the evening sky.  The giant planet now sets just an hour after the Sun, so your only chance to see him is in the brighter stages of evening twilight.  You’ll have one last opportunity to catch him with a thin crescent Moon on the evening of the 28th when Luna will be just to the south of the planet.  Jupiter will pass behind the Sun on July 24th, and early risers can expect to see him rising in the morning skies by early August.

Mars is now the most prominent planet in the evening sky, thanks in most part to his distinctive color.  Although he is only slightly brighter than Saturn his reddish tint makes him stand out in a field that’s otherwise sprinkled with white- or blue-tinted stars.  He continues to gain speed in his easterly trek around the sky, and this week he’ll move just over 2.5 degrees closer to the bright star Spica in Virgo.  In another two weeks he’ll pass just over a degree to the north of the star.  Through the telescope his disc has now dwindled to less than 10 arcseconds’ diameter, making it difficult for the small telescope owner to see much more than a pink gibbous dot.

Although he is still outshone by Mars, Saturn is the planet of choice for summertime observing.  Despite his southerly declination, the ringed planet is well-placed for viewing during the mid-evening hours.  Almost any form of optical aid will show the planet’s distinctive rings, and the larger the aperture you use to scrutinize him the more detail you’ll see in these mysterious appendages.  We now know that the rings are composed of billions of chunks of ice in various sizes and that their apparent structure is regulated by a swarm of small moons both inside and outside the brighter ring components.  They are also truly enormous; the distance across the visible ring system spans over 70% of the mean distance from the Earth to the Moon.  However, they are also incredibly thin, probably less than 100 meters thick!

Venus remains pretty much where she’s been for the past several weeks, wallowing in morning twilight just above the eastern horizon.  About all you can see is her slow drift toward the north as she traverses the northern reaches of the ecliptic.

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The Sky This Week : June 17 – 24, 2014 !

The Sky This Week, 2014 June 17 – 24

Celestial sights for the shortest nights.
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The summer Milky Way from Cassiopeia to Sagittarius
imaged from Morattico, Virginia

The Moon spends the week wandering through the star-poor constellations in the early morning sky.  Last Quarter occurs on the 19th at 2:39 pm Eastern Daylight Time.  Luna won’t encounter any bright objects until the pre-dawn hours of the 24th, when her waning crescent will be just over two degrees to the south of bright Venus in the gathering morning twilight.

This week we experience the shortest nights of the year as we mark the summer solstice at 6:51 am EDT on the 21st.  At this time the center of Old Sol’s disc stands directly above the Tropic of Cancer over the border between Libya and Chad on the African continent.  Here in Washington we will experience 14 hours 54 minutes of daylight for most of the week before the length of day begins to slowly recede.  Thanks to our planet’s elliptical orbit our latest sunset won’t occur until the 28th.

You’ll have to stay up pretty late in order to take advantage of the Moonless skies around the time of the solstice.  Even though the Sun sets at around 8:37 pm the end of evening astronomical twilight doesn’t occur until two hours later.  However, it’s worth your while to wait for darkness if you happen to be in a good dark location well away from city lights.  Summer is the season to enjoy the panoply of the brightest stretches of the Milky Way, our home galaxy, which arches across the sky during the darkest hours.  By 1:00 am the densest part of the galaxy straddles the southern horizon as we peer toward its core some 30,000 light-years away in the direction of the constellation of Sagittarius.  The galactic center itself is hidden from our direct view by dense clouds of stars and associated star-stuff.  While they cloak the Milky Way’s core with mystery, they are wonderful targets for binoculars and small telescopes.  I have spent many hours in a beach chair poking around these star-filled regions with a simple pair of binoculars marveling at the vast numbers of faint stars that form the galaxy’s soft glow along with the bright knots of star clusters and faintly glowing gas clouds known as “nebulae”.  On very clear nights it is also interesting to look at the spaces where the stars appear absent.  These “dark nebulae” are actually cold clouds of gas and dust that contain the building blocks of new stars, planets, and even life forms.  Exploring the Milky Way is always a highlight of my summer vacation.

The early summer evenings are still dominated by the glimmer of three bright planets, but one of them is rapidly leaving us.  Giant Jupiter, which has dominated the night sky since the beginning of the year, is now just weeks away from conjunction with the Sun.  Old Jove still shines brightly in the west as twilight deepens, but he now sets just after 10:00 pm.  He still shines at a bright -1.8 magnitude, and he seems to be bidding me farewell when I set my telescope up in the front yard, shining through a gap between the houses across the street.  About all I can see of him now is his undulating disc and the fuzzy blobs of his four bright Galilean moons.

Mars is also a bright object that’s hard to miss.  You’ll find the red planet in the southwestern sky as twilight deepens and ends, betrayed by his distinctive ruddy hue.  Mars is picking up speed as he wends his way eastward along the ecliptic and closes in on the bright blue star Spica.  Once he passes the star in another couple of weeks he will begin a rapid dash along the ecliptic in a race with the encroaching Sun.  He’ll pay a call on many of the bright stars of summer as he lingers in the southwest for the rest of the year.

Saturn is now the planet of choice for the small telescope owner.  He transits the meridian just after 10:00 pm, so he’s well-placed for viewing during “prime-time”.  Saturn’s rings are now generously tipped toward our line of sight, and a telescope of four inches or more aperture will show the dark gap known as Cassini’s Division that separates the outermost ring from the brighter inner one.  This division is an actual gap that’s about as wide as the diameter of Mars; it is caused by a gravitational resonance with the innermost of Saturn’s larger moons.  Any telescope should show the planet’s brightest moon Titan, but you’ll need six or more inches to spy many of the smaller ones.

Venus gets a visit from the thin crescent Moon by the week’s end.  For the next couple of month she will rise at the beginning of morning twilight, so you will have to seek her in a brightening sky.  Fortunately she stands out quite well under these conditions, so you shouldn’t have any trouble spotting her other than waking up before sunrise!

The Sky This Week : June 10 – 17, 2014 !

The Sky This Week, 2014 June 10 – 17

What’s up under the Honey Moon?
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The Moon, Mars, and Spica over the Washington Monument
Imaged at the 5th annual Astronomy Festival on the Mall,
2014 June 6

The Moon descends to the southern reaches of the ecliptic this week, brightening up the rising southern summer constellations.  Full Moon occurs on the 13th at 12:11 am Eastern Daylight Time.  June’s Full Moon is variously known as the Mead Moon, Rose Moon, Strawberry Moon, or Honey Moon.  All of these names reflect Luna’s appearance at her low southerly declination, since the haze and humidity of the midsummer air tends to give a warmer tint to her otherwise silvery face.  On the evening of the 10th you’ll find her just east of golden Saturn.  On the following night look for the ruddy star Antares just over seven degrees south of the Moon.  By the end of the week she sets off for the long climb through the rising autumnal stars.

Those of you who are not “morning people” (and I count myself among you) can take heart as this week finds the earliest sunrises of the year.  On June 14th Old Sol breaks the Washington horizon at 5:42 am EDT, and as the week ends his rise time begins to slowly creep back toward a more civilized hour.  However, due to the elliptical nature of the Earth’s orbit we won’t see the latest sunset until the 28th, when the Sun retires at 8:38 pm.  In between we find the summer solstice falling on the 21st.  This is the day with the longest duration of daylight as the Sun stays above the DC horizon for 14 hours and 54 minutes.

The bright Moon and the year’s shortest nights limit our nighttime skywatching to the brightest objects in the sky.  Fortunately, besides the planets, there are other objects that we can pick out without having to stay up all night long.  The first or these is the bright star Arcturus, which stands high on the meridian at around 10:00 pm.  Arcturus is the brightest star in the northern hemisphere sky and the fourth brightest in the entire heavens.  Its rosy tint tells us that it is a star that has evolved into its early giant stage, fusing hydrogen is a shell around an inert helium core.  It is the closest star of this type to the Sun, located just under 37 light-years away.  Its light was used to open the 1933 Chicago World’s Fair; at the time it was thought to be 40 light-years distant, and it had been 40 years since the World Columbian Exposition was staged in Chicago in 1893.

By midnight you should see the signature stars of summer high in the eastern sky.  Vega, Deneb, and Altair form the distinctive asterism known as the Summer Triangle, and the area around these stars will provide you with hours of delightful views through binoculars, especially once the Moon pulls away.  Some of the densest star clouds of the Milky Way are contained in the Triangle’s environs with a host of small asterisms and loose star clusters sprinkled along the way.

Jupiter can still be seen shortly after sunset in the western sky, but you have to act fast to get a quick glimpse of him in the telescope.  By the 15th he sets at the end of evening twilight, so if you do catch a glimpse of him it will be against a bright sky background.  In another month he’ll slip behind the Sun, then we’ll have to wait until the winter to see him in the evening sky again.

Mars still shines with his distinctive ruddy glow as the evening twilight deepens.  The red planet now spends his evenings on the west side of the meridian to the west of the bright star Spica in the constellation of Virgo.  Mars is picking up speed as he begins to move eastward along the ecliptic, and by mid-July he’ll race past the blue-tinted star.  Mars’ disc continues to shrink in the telescope eyepiece, so sighting detail on his ruddy surface requires lots of patience and a steady atmosphere.

Saturn is now well-placed for viewing as evening twilight fades to darkness.  The ringed planet now crosses the meridian at around 11:00 pm, so you’ll have several hours to enjoy telescopic views of him.  Despite his low declination, in steady air you should be able to spot the Cassini Division in the planet’s icy rings in a four-inch or larger telescope, and the more aperture you can command the more of his bevy of moons will reveal themselves.

Venus continues to play cat-and-mouse with the rising Sun, visible low in the east in gathering morning twilight.  This week she moves from the constellation of Aires into Taurus, and next week she will glide to the south of the Pleiades star cluster.

The Sky This Week : June 3 – 10, 2014 !

The Sky This Week, 2014 June 3 – 10

Come see the sky on the National Mall!
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Lunar surface features at low sun angle, 2014 May 7

The Moon waxes in the evening sky this week, wending her way through the springtime constellations.  First Quarter occurs on the 5th at 4:39 pm Eastern Daylight Time.  Look for Luna just two degrees south of ruddy Mars on the evening of the 7th.  On the 8th she glides past the bright star Spica in the constellation of Virgo.  The Moon then parks herself just east of Saturn on the evening of the 10th.

This is another good week to acquaint yourself with the varied landscapes of our closest neighbor in space.  As the terminator reveals more of the Moon’s disc each night, new features come into view while those that were prominent the night before take on a different aspect under the higher Sun angle.  It is always fascinating to see how individual landmarks appear to evolve as the local lighting changes.  Fine details on small craters, rilles, and other surface features stand out shortly after the terminator reveals them, but a day later they are washed out under the Sun’s relentless glare.

You’ll have a great opportunity to look at the Moon as well as the planets Jupiter, Mars, and Saturn and other celestial sights if you come down to the Washington Monument grounds on the evening of June 6th.  We will be participating in the fifth annual Astronomy Festival on the National Mall that evening between 6:00 pm and 11:00 pm EDT, weather permitting.  The program, sponsored by Hofstra University, will feature a number of telescopes provided by local astronomers as well as demonstrations and talks by amateur and professionals in the field.  Last year we hosted some 1500 people and about two dozen telescopes.  We’re hoping for a repeat this year.  Details and directions to the event may be found here.

We may still be able to get a telescopic peek at the shy planet Mercury at the festival, but your chances of spotting this elusive planet with the naked eye are now getting pretty slim.  Mercury is now racing toward conjunction with the Sun on June 19th, so he’s dropping from the evening sky like a stone.  I managed to get a peek at him through the telescope last weekend at Sky Meadows State Park on the Virginia Blue Ridge, but I only had about 10 minutes to view him before he dropped below the ridgeline.

Jupiter should still be an easy target shortly after sunset.  The giant planet can still be found in the western sky, but he’s only about 20 degrees high at 9:00 pm when the sky will be dark enough to show his Galilean moons.  Looking at Old Jove under these conditions id a bit like looking at him at the bottom of a swimming pool; atmospheric turbulence and refraction blur out almost all of the fine detail, but under decent conditions you should still be able to see his prominent equatorial cloud belts. 

Mars will be on the meridian at 9:00 pm for the festival, and we’ll try our best to provide good views of the red planet’s dusty disc.  His apparent diameter will only be about one-third that of Jupiter, but his position higher in the sky should be less subject to atmospheric effects.  Fortunately the planet will be showing a side that has some of the most prominent dark albedo features, and two bright white areas should be visible near the planet’s limbs.  The larger of the two is a huge depression on Mars’ surface known as Hellas.  Similar to the large “seas” on the Moon, this basin is the result of a huge impact that occurred very early in Mars’ history.  It tends to fill with clouds and fog, so it is often mistaken for a polar ice cap.  The true north polar ice cap is smaller but stands out as a tiny bright spot on the opposite limb.

Saturn should be the star of the festival, and during the course of the evening I’m sure just about every telescope will point toward the ringed planet.  In steady air Saturn presents one of the most captivating sights in the sky as the sphere of the planet seems to magically balance in the center of the rings.  The rings themselves look almost razor sharp, and indeed in reality they are the flattest and thinnest structures known in the universe.  The distance across the outer rings as about three quarters the distance from the earth to the Moon, yet they are only about 100 meters thick!  They are kept in place by the gravity of the planet and its innermost moons, and it is these small icy worlds that cause the gaps that one can see in the rings through modest telescopes.

You won’t see Venus at the festival, though.  She doesn’t rise until shortly before the Sun, but if you’re up early on any morning you’ll find her blazing away in the gathering twilight, low in the eastern sky.  She is resolutely marching in the wake of the Sun, and in another few weeks you’ll see her in the company of some of the stars of early winter!