Archive for July, 2014

The Sky This Week , July 15 – 22, 2014 !

The Sky This Week, 2014 July 15 – 22
Under a river of stars…
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Messier 20, the “Trifid Nebula” in Sagittarius
Imaged 2014 July 5 from near Morattico, Virginia
80mm f/6 Antares Sentinel refractor with Canon EOS Rebel T2i DSLR

The Moon wanes in the early morning sky this week, reaching Last Quarter on the 18th at 10:08 pm Eastern Daylight Time. Luna wends her way through the sparse starfields of the autumnal constellations before encountering the first stars of winter by week’s end. Look for Luna just over a degree northwest of the bright star Aldebaran before dawn on the 22nd.

As the Moon slips into the morning sky the evening hours are once again graced by darkness, allowing us to view the splendor of the brightest parts of our home galaxy, the Milky Way. One of the highlights of summer for me is to travel to locations far from city lights, preferably near the water, and just sit back in a lawn chair to watch the ghostly glow of diffuse light slowly wheel overhead as the night passes. There are many subtle features that can be seen with the unaided eye. Perhaps the most fascinating of these are the dark “rifts” that intersperse the brighter star clouds, especially in the areas of the constellations of Cygnus, Aquila, Ophiuchus, and Sagittarius. These dark areas are vast clouds of cold gas and dust that mark the plane of the galaxy’s disc, and it is in these regions that the raw ingredients for the formation of stars and planets may be found. These rifts continue well below the southern horizon where they were noted by many pre-Columbian cultures, and especially the Inca. To these ancient inhabitants of the spine of the Andes the dark shapes in the sky were their equivalent of our constellations, and much of their sky lore is made up on these patterns of darkness. The American astronomer Edward Emerson Barnard pioneered the photographic cataloging of the Milky Way’s dark regions, eventually compiling a catalog of 370 discrete dark areas. You can spot many of these dark areas with a pair of binoculars as you peruse the Milky Way on a clear July night. You can also spot dozens of bright knots of stars and wispy patches of gaseous nebulae with this simple optical aid. My favorite telescope for viewing the Milky Way is a small 80mm (3.1-inch) refractor with a wide-field eyepiece. This breaks up many of the galaxy’s brighter areas into clouds of innumerable stars crisscrossed by some of Barnard’s “dark nebulae” as well as the brighter star clusters and glowing gas clouds recorded by the French astronomer Charles Messier. This, to me, is a perfect summer night!

In the evening sky we still have some planets to view, but our time with them is growing shorter with each passing week. Ruddy Mars is now on the run from the advancing Sun, and you can watch his nightly progress as he drifts eastward from the bright blue star Spica. The red planet is now well over a full magnitude fainter than he was at opposition back in April and his telescopic disc is now just over half his apparent opposition diameter. Mars will continue to gather speed against the stars over the next few weeks, so he will remain a fixture, albeit a fading one, in the southwestern sky for the rest of the year.

Saturn reaches the second stationary point in this year’s apparition on the 21st. It will be hard to notice his resumption of direct eastward motion for several more weeks, though, since he takes nearly 30 years to make one complete circuit of the sky. He is well-placed for viewing through the telescope from about an hour after sunset until around midnight, and it’s well worth the time to give him a look. We are now seeing the ringed planet close to his maximum phase angle, which means that the planet’s disc now casts its longest shadow on the rings for a pleasing, near-“3D” effect.

If you’re up before the Sun at around 5:00 am you should have no trouble spotting Venus low in the southeastern sky each morning. You may also notice a couple of bright stars forming a large triangle with the planet. These stars are Capella and Aldebaran, and they help to remind us that the seasons inexorably change. By the time these stars are prominent in the evening sky the memories of hot July nights under the Milky Way will be a distant memory.

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The Sky This Week , July 8 – 15, 2014 !

The Sky This Week, 2014 July 8 – 15
A tale of two red stars.
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Conjunction of the Moon and Mars, 2014 July 6, 02:19 UT

The Moon brightens the evening sky this week, passing through the full phase as she crosses the heart of the summer Milky Way. Full Moon occurs on the 12th at 7:25 am Eastern Daylight Time. July’s Full Moon is popularly known as the Thunder Moon, but it is also known as the Buck Moon, Hay Moon, or Hot Sun Moon. Look for the Moon about two degrees northwest of the star Graffias, the northernmost of the three stars that form the head of Scorpius, the Scorpion on the evening of the 8th . On the 9th she stands just under 10 degrees northeast of the bright star Antares. She ends the week drifting eastward among the faint starfields of the rising autumnal constellations.

The bright light of the Moon keeps us from enjoying the spectacle of the summer Milky Way, but the season’s bright stars still offer some interesting sights and stories. Last week we discussed Antares, the bright reddish star in the heart of Scorpius. There are some very interesting parallels between this star and its counterpart, Betelgeuse, in the winter constellation of Orion. Both stars are highly-evolved “red supergiant” stars, far along on their evolutionary tracks. As the hydrogen in their cores is exhausted, it begins to fuse into helium in an ever-expanding shell around the core. This forces the stars’ girths to expand dramatically. If either star occupied the Sun’s position in our solar system the Earth would be located inside the tenuous outer layers of these swollen monsters. As their size increases their surface areas grow exponentially and become much cooler, giving them their characteristic reddish hue. The other stars in their respective constellations are hot young “blue giant” stars that recently formed from huge clouds of interstellar dust and gas; the three stars that form the “head” of the Scorpion are thus very similar to the three stars that form the “belt” of the Hunter. Despite the fact that the constellations are opposite each other in the sky, they are also linked by sky lore. The boastful mortal Orion claimed domination over all animals on the Earth, a claim also made by the goddess Diana. To teach Orion a lesson, Diana sent a scorpion to remind the Hunter of his mortal status. The scorpion stung Orion on the heel with what proved to be a fatal wound just before Orion dispatched it. Diana, secretly in love with Orion, placed both combatants in the sky but made sure they were opposite each other. Indeed, here in Washington, you’ll find that Betelgeuse sets about 20 minutes after Antares rises. The one-time adversaries now perpetually chase each other around the sky.

Mars is now steadily pressing eastward along the ecliptic, and you can get an idea of how fast he’s moving by watching him overtake and pass the bright star Spics. As the week opens the red planet is just under three degrees from the star, and he closes the gap to just a bit over one degree on the night of the 13th. By the end of the week he’ll be northeast of the star and setting his sights on distant Saturn. While not quite as eye-catching as last week’s close lunar conjunction, this should be a fun event to observe.

Saturn is still putting on a good show in the evening sky, but he’s now well west of the meridian as darkness finally falls. His slow retrograde motion is now grinding to a halt, and he’ll become stationary on the 21st. For the next several weeks he will stay just over two degrees northeast of the star Zubenelgenubi before gathering eastward momentum in the late summer sky. The ringed planet is now the sole telescopic showpiece planet in the sky, so be sure to catch a glimpse of him while you can. I spent the recent holiday weekend with my little three-inch travel scope, and even at a paltry 26 power the planet’s rings were easily visible.

Bright Venus continues to drift eastward among the rising stars of winter as she keeps pace with the Sun. This week she passes between the horns of Taurus, the Bull, but you’ll be hard-pressed to see this against the brightening sky of morning twilight. Venus herself will stand out like a beacon.

The Sky This Week , July 1 – 8, 2014 !

The Sky This Week, 2014 July 1 – 8

Bright stars and fireworks highlight the 4th.
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Saturn, imaged 2014 June 23, 01:48 UT

The Moon waxes in the evening sky this week as she dives toward the southern reaches of the ecliptic.  First Quarter occurs on the 5th at 7:59 am Eastern Daylight Time.  Luna has a busy week, sharing the sky with fireworks on the 4th, the red planet Mars on the 5th, and Saturn on the 7th.  The Moon will occult these bright planets for residents of the southern hemisphere.  She ends the week among the stars that form the head of Scorpius, the Scorpion.

Earth reaches aphelion, its farthest point from the Sun, on the 3rd at 4:13 pm EDT.  At this time we’ll be just over 94,550,000 miles (153,000, 000 kilometers) from the day-star.  Six months from now, in early January, we’ll find ourselves closest to the Sun by a mere 3 million miles or so.  Fortunately this annual excursion means that the planet’s orbit is nearly circular, so our climate remains relatively benign throughout the year.

While you’re out side waiting for the fireworks to begin (or waiting for the crowds to thin before heading home!) there are a number of bright objects in the sky that you can see despite the moonlight and the dazzle from the sparkling displays.  High overhead in the mid-evening hours you’ll find the bright star Arcturus, the brightest star in the northern sky.  This star sports a golden hue because it is a star that’s evolving toward old age.  Like some people, the star’s girth expands as it exhausts the hydrogen in its core, and as it expands its surface becomes a little cooler and redder.  Contrast this with Spica, the bright blue-tinted star that’s now just a few degrees from Mars in the southwest.  Moving toward the east, you’ll find Saturn hovering near a second-magnitude star called Zubenelgenubi, the brightest star in the otherwise nondescript constellation of Libra, the Scales.  This star is a fine example of a “binocular double” star whose components share the same proper motion and parallax and therefore must be gravitationally linked.  Continuing eastward past Saturn you’ll run into the distinctive figure of Scorpius, with the ruddy star Antares marking the celestial scorpion’s hear.  The star’s name means “rival of Mars”, and comparing the two objects reveals why that name is appropriate.  Now turn your gaze high to the eastern sky where a trio of bright blue stars awaits.  The brightest of these is Vega, lead star in the constellation of Lyra, the Harp.  This star is relatively close-by at about 27 light-years, but even closer to us is Altair, faintest and southernmost of the trio.  Altair is a mere 16 light-years away, making it one of the nearest bright stars in the sky.  The final star in the Summer Triangle is Deneb, which outwardly appears to be on par in brightness with Altair.  However, Deneb is nearly 100 times farther away from us, making it one of the most intrinsically luminous stars in the sky.  It shines with a luminosity some 65,000 times that of the Sun!

It’s time to bid Jupiter a fond farewell.  The giant planet now sets less than an hour after sunset, and you’ll be hard-pressed to see him in the glare and haze of evening twilight.  However, in a month of so he’ll be rising to greet early morning commuters and have a spectacular rendezvous with Venus.

Mars shares the early evening sky with Saturn and Spica, but you won’t have any trouble recognizing him thanks to his distinctive rosy glow.  The red planet is rapidly closing the gap with the star Spica, and in another week he’ll drift past the star as he heads eastward along the ecliptic.  Mars’ disc continues to shrink for telescopic observers, but you may still be able to make out a few details on nights with extremely steady air.

Saturn now straddles the meridian at around 9:30 pm.  After the Moon the ringed planet is the most telescopically rewarding sight foe telescope “newbies”.  Almost everyone lets out a gasp the first time they see this distant frozen world and his marvelous rings, and even us seasoned veterans at the eyepiece pause to take a good, long look.  It is hard to believe that 10 years ago the Cassini space probe dropped into orbit around Saturn and a year later parachuted the Huygens probe into the smoggy atmosphere of its largest moon Titan.  The images that the Cassini mission has gathered over that time are simply astonishing.  You can browse Cassini’s “greatest hits” at the mission’s website.

Bright Venus continues to dazzle early risers as morning twilight gathers.  Look for her in the north-northeast sky, rising about an hour before the Sun.