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Friday, October 24 2014 @ 01:46 PM CDT

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Thank Goodness the Sun is Single

NASA Space PlaceBy Trudy E. Bell

  
Planetary collisions such as shown in this artist’s rendering could be quite common in binary star systems where the stars are very close.
Click image for larger view
It’s a good thing the Sun is single. According to new research, Sun-like stars in close double-star systems “can be okay for a few billion years — but then they go bad,” says Jeremy Drake of the Harvard-Smithsonian Astrophysical Observatory in Cambridge, Mass.

How bad? According to data from NASA’s Spitzer Space Telescope, close binary stars can destroy their planets along with any life. Drake and four colleagues reported the results in the September 10, 2010, issue of The Astrophysical Journal Letters.

Our Sun, about 864,000 miles across, rotates on its axis once in 24.5 days. “Three billion years ago, roughly when bacteria evolved on Earth, the Sun rotated in only 5 days,” explains Drake. Its rotation rate has been gradually slowing because the solar wind gets tangled up in the solar magnetic field, and acts as a brake.

But some sun-like stars occur in close pairs only a few million miles apart. That’s only about five times the diameter of each star — so close the stars are gravitationally distorted. They are actually elongated toward each other. They also interact tidally, keeping just one face toward the other, as the Moon does toward Earth.

Such a close binary is “a built-in time bomb,” Drake declares. The continuous loss of mass from the two stars via solar wind carries away some of the double-star system’s angular momentum, causing the two stars to spiral inward toward each other, orbiting faster and faster as the distance shrinks. When each star’s rotation period on its axis is the same as its orbital period around the other, the pair effectively rotates as a single body in just 3 or 4 days.

Then, watch out! Such fast spinning intensifies the magnetic dynamo inside each star. The stars “generate bigger, stronger ‘star spots’ 5 to 10 percent the size of the star — so big they can be detected from Earth,” Drake says. “The stars also interact magnetically very violently, shooting out monster flares.”

Worst of all, the decreasing distance between the two stars “changes the gravitational resonances of the planetary system,” Drake continued, destabilizing the orbits of any planets circling the pair. Planets may so strongly perturbed they are sent into collision paths. As they repeatedly slam into each other, they shatter into red-hot asteroid-sized bodies, killing any life. In as short as a century, the repeated collisions pulverize the planets into a ring of warm dust.

The infrared glow from this pulverized debris is what Spitzer has seen in some self-destructing star systems. Drake and his colleagues now want to examine a much bigger sample of binaries to see just how bad double star systems really are.

They’re already sure of one thing: “We’re glad the Sun is single!”

Read more about these findings at the NASA Spitzer site at http://www.spitzer.caltech.edu/news/1182-ssc2010-07-Pulverized-Planet-Dust-May-Lie-Around-Double-Stars . For kids, the Spitzer Concentration game shows a big collection of memorable (if you’re good at the game) images from the Spitzer Space Telescope. Visit http://spaceplace.nasa.gov/en/kids/spitzer/concentration/.

This article was provided by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration.
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Planets in Strange Places

NASA Space PlaceBy Trudy E. Bell

  
Artist’s rendering compares size of a hypothetical hypergiant star and its surrounding dusty disk to that of our solar system.
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Red star, blue star, big star, small star — planets may form around virtually any type or size of star throughout the universe, not just around mid-sized middle-aged yellow stars like the Sun. That’s the surprising implication of two discoveries in 2006 from the 0.85-meter-diameter Spitzer Space Telescope, which is exploring the universe from orbit at infrared (heat) wavelengths blocked by the Earth’s atmosphere.

At one extreme are two blazing, blue “hypergiant” stars 180,000 light-years away in the Large Magellanic Cloud, one of the two companion galaxies to our Milky Way. The stars, called R 66 and R 126, are respectively 30 and 70 times the mass of the Sun, “about as massive as stars can get,” said Joel Kastner, professor of imaging science at the Rochester Institute of Technology in New York. R 126 is so luminous that if it were placed 10 parsecs (32.6 light-years) away — a distance at which the Sun would be one of the dimmest stars visible in the sky — the hypergiant would be as bright as the full moon, “definitely a daytime object,” Kastner remarked.

Such hot stars have fierce solar winds, so Kastner and his team are mystified why any dust in the neighborhood hasn’t long since been blown away. But there it is: an unmistakable spectral signature that both hypergiants are surrounded by mammoth disks of what might be planet-forming dust and even sand.

At the other extreme is a tiny brown dwarf star called Cha 110913-773444, relatively nearby (500 light-years) in the Milky Way. One of the smallest brown dwarfs known, it has less than 1 percent the mass of the Sun. It’s not even massive enough to kindle thermonuclear reactions for fusing hydrogen into helium. Yet this miniature “failed star,” as brown dwarfs are often called, is also surrounded by a flat disk of dust that may eventually clump into planets. (This brown dwarf discovery was made by a group led by Kevin Luhman of Pennsylvania State University.)

Although actual planets have not been detected (in part because of the stars’ great distances), the spectra of the hypergiants show that their dust is composed of forsterite, olivine, aromatic hydrocarbons, and other geological substances found on Earth.

These newfound disks represent “extremes of the environments in which planets might form,” Kastner said. “Not what you’d expect if you think our solar system is the rule.” Hypergiants and dwarfs? The Milky Way could be crowded with worlds circling every kind of star imaginable — very strange, indeed.

Keep up with the latest findings from the Spitzer at www.spitzer.caltech.edu. Kids and their grownup friends can enjoy beautiful images from Spitzer while playing Spitzer Concentration at The Space Place (spaceplace.nasa.gov/en/kids/spitzer/concentration).

This article was provided by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration.
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Astronomers Stumble onto Huge Space Molecules

NASA Space PlaceBy Trudy E. Bell and Tony Phillips

  
Superimposed on a Spitzer infrared photo of the Small Magellanic Cloud is an artist's illustration depicting a magnified view of a planetary nebula and an even further magnified view of buckyballs, which consist of 60 carbon atoms arranged like soccer balls.
Click image for larger view
Deep in interstellar space, in a the swirling gaseous envelope of a planetary nebula, hosts of carbon atoms have joined together to form large three-dimensional molecules of a special type previously seen only on Earth. Astronomers discovered them almost accidentally using NASA's Spitzer Space Telescope.

“They are the largest molecules known in space,” declared Jan Cami of the University of Western Ontario, lead author of a paper with three colleagues published in Science online on July 22, 2010, and in print on September 3.

Not only are the molecules big: they are of a special class of carbon molecules known as “fullerenes” because their structure resembles the geodesic domes popularized by architect Buckminster Fuller. Spitzer found evidence of two types of fullerenes. The smaller type, nicknamed the “buckyball,” is chemical formula C60, made of 60 carbon atoms joined in a series of hexagons and pentagons to form a spherical closed cage exactly like a black-and-white soccer ball. Spitzer also found a larger fullerene, chemical formula C70, consisting of 70 carbon atoms in an elongated closed cage more resembling an oval rugby ball.

Neither type of fullerene is rigid; instead, their carbon atoms vibrate in and out, rather like the surface of a large soap bubble changes shape as it floats through the air. “Those vibrations correspond to wavelengths of infrared light emitted or absorbed—and that infrared emission is what Spitzer recorded,” Cami explained.

Although fullerenes have been sought in space for the last 25 years, ever since they were first identified in the laboratory, the astronomers practically stumbled into the discovery. Co-author Jeronimo Bernard-Salas of Cornell University, an expert in gas and dust in planetary nebulae, was doing routine research with Spitzer's infrared observations of planetary nebulae with its spectroscopy instrument. When he studied the spectrum (infrared signature) of a dim planetary nebula called TC 1 in the southern — hemisphere constellation of Ara, he noticed several clear peaks he had not seen before in the spectra of other planetary nebulae.

“When he came to me,” recounted Cami, an astrophysicist who specializes in molecular chemistry, “I immediately and intuitively knew it I was looking at buckyballs in space. I've never been that excited!” The authors confirmed his hunch by carefully comparing the Tc 1 spectrum to laboratory experiments described in the literature.

“This discovery shows that it is possible — even easy — for complex carbonaceous molecules to form spontaneously in space,” Cami said. “Now that we know fullerenes are out there, we can figure out their roles in the physics and chemistry of deep space. Who knows what other complex chemical compounds exist—maybe even some relevant to the formation of life in the universe!”

Stay tuned!

Learn more about this discovery at http://www.spitzer.caltech.edu. For kids, there are lots of beautiful Spitzer images to match up in the Spitzer Concentration game at http://spaceplace.nasa.gov/en/kids/spitzer/concentration.

This article was provided by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration.
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Astronomy From Your Back Yard - 1/5 to 1/11 2011

By Dave Grosvold

  
Happy New Year! Things are “looking up” in backyard astronomy — at least for the remainder of this week. With the skies relatively clear until the weekend, and the waxing crescent Moon, the resulting sky glow is not bright enough to present much of a problem for evening sky watchers.

  
One of the most spectacular sights to be had for amateur astronomers on these cold clear winter evenings is the central region of the constellation of Orion. This region is home to large bright nebulae and open clusters easily visible in a small telescope or binoculars. I mentioned M42, the Great Orion Nebula which is the brightest deep sky object in this region last year at this time.

Two objects in this area besides M42 are special treats. The first, NGC 1977, is known as the Running Man Nebula. NGC 1977 is a beautiful blue emission nebula with a dark reflection nebula inside it. Because of the reflected glow from brighter and larger M42, the darker parts of NGC 1977 reflects the colorful hues of M42 and imbue it with a mysterious, ghostly quality. Some have come to refer to NGC 1977 as the Ghost Nebula for this reason.

  
The second object, NGC 1981, is a large open cluster just above NGC 1977. NGC 1981 is a beautiful sprinkling of 10 or 11 bright stars in the Orion-Cygnus Arm of the Milky Way Galaxy, peppered with a background of the much more distant stars of other regions of the Milky Way. All of the stars in the cluster and the two nebula mentioned above are relatively close neighbors of the Solar System, at a mean distance of only about 700 light years from Earth. This makes it one of the nearest star forming regions we have available for study.

Two other deep sky objects in this region surround the star known as Alnitak, or Zeta Orionis (ζ Ori.) This triple star system, the easternmost star in the Belt of Orion, is surrounded by two well-known faint emission nebula, B33, the Horsehead Nebula, and NGC 2024, the Flame Nebula. These are normally not visible in small telescopes or binoculars, but they are a popular target for astro-imagers.

  
By 7:30 PM CST Wednesday evening, the Moon has set and the Winter Triangle is well up in the east-southeast, consisting of Betelgeuse in Orion's leftmost corner, bright Sirius in Canis Major below and to the right, and Procyon in Canis Minor to the left of these two. The Winter Triangle is brighter and more colorful than it's well-known summer counterpart. An even larger asterism, the Winter Hexagon, includes Procyon and Sirius, along with four other bright, colorful stars in the eastern evening sky: Rigel in Orion; Aldebaran in Taurus; Capella in Auriga; and Pollux in Gemini.

  
The brightest "star" in the evening sky this week is NOT a star, but a planet! As the current Evening Star, Jupiter still shines at magnitude -2.3 in Pisces, high in the south above Fomalhaut in Piscis Austrinus. Jupiter is receding from us as Earth begins to round the far side of the Sun from Jupiter, so it appears only 38 arcseconds wide. However, Jupiter is still wide enough to see the South Equatorial Belt re-forming and the transits of the Great Red Spot in a small-to-medium telescope. Uranus is now very close to Jupiter, just 0.6° to the west of the larger planet. Both planets should be close enough so they are both visible in the same field of view in a small telescope when using a medium power eyepiece. A third planet, Neptune, is also still visible in the early evening southwestern sky west of Fomalhaut, on the border between Aquarius and Capricornus. This one is much harder to spot and requires a small telescope or binoculars.

Bright Saturn rises about 30 minutes past midnight this week. By 3:30 AM CST, Saturn is in a perfect position for viewing, high in the southeastern sky in Virgo. That puts it above the thick lower atmosphere long before the sky glow begins in the east as the rising Sun approaches the horizon. The rings are tilted now at about 10°, widening as spring approaches. The rings haven't been this wide since 2007.

Later in the morning this week, very near dawn, Venus shines in the southeastern sky. Though very bright at magnitude -4.3, viewing Venus, in a telescope reveals itself to be only half-lit. Venus is very nearly at it's greatest elongation from the Sun. Venus will begin to grow gibbous in the coming months, while shrinking in diameter as it begins to swing around the far side of the Sun in its faster orbit.

Mercury, too, will be relatively bright at magnitude 0, low in the southeastern sky just before dawn. Notice fainter Antares in Scorpius and the rest of the starry background of the Milky Way, rising in the east before dawn as the winter season marches on.
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Astronomy From Your Back Yard - 12/15 to 12/21 2010

Backyard Astronomy Extra - Total Lunar Eclipse!

By Dave Grosvold

  
  
On Saturday evening, look just to the left of the Moon a mere 2° for the delicate Pleiades star cluster. The Pleiades is a beautiful, fairly tight open cluster in Taurus that was used by Native American tribes to test the eyesight of their scouts. See if you can see more than 5 stars in the Pleiades with the naked eye. If so, then you would have qualified as a scout in the Old West. This week, you may need to use binoculars to see the Pleiades due to the overwhelming glare of the waxing gibbous Moon.

Below the Pleiades by about a fist-width is orange Aldebaran. Aldebaran is part of the Hyades star cluster, an open star cluster in Taurus that looks to most like a small “V” laying on its side in the eastern sky. Far off to the left of the Hyades shines brighter yellow Capella. On Sunday evening, the Moon is to the left of the Hyades, and just to the left of a small star named Tau Tauri (τ Tau). By Monday evening, the Moon has moved just to the left of Zeta Tauri (ζ Tau.) By now, you've realized that the Moon has taken three nights to pass from one end of Taurus to the other.

  
   Click image for larger view
But the REAL highlight of the week is still yet to come. On Tuesday morning, the Full Moon occurs right at the mid-point of a total lunar eclipse! Make plans now to see this last lunar eclipse of the year. The eclipse begins just after midnight in the early-morning hours of Tuesday, December 21, 2010.

  
The eclipse reaches its mid-point at about 2:17 AM CST Tuesday morning. The Moon will be shining brightly very high in the early-morning sky during the eclipse, in the south-southeast. By the time it reaches mid-eclipse, the Moon will be high in the southwest, and will drop into the western sky by the end of the eclipse at 4:01 AM. The best way to view this eclipse is with a pair of binoculars or a small telescope.

The dim Little Dipper (Ursa Minor) hangs just about straight down from the North Star by about 9:30 PM all this week, as if it was hung from a hook on the wall of the sky. The brighter Big Dipper (Ursa Major) is rearing upward on its handle low in the north-northeast. You can easily find Polaris, (or the North Star,) by using the two end stars of the bowl of the Big Dipper.

  
Venus shines with a brilliant light in the southeastern sky this week before and during dawn. Venus now rises about two hours before the first light of dawn (about 3:45 AM CST,) and rises to an altitude of about 33° before getting lost in the glare of the rising Sun. While it's till dark, look for fainter Spica well to Venus' upper right, and for Saturn above Spica. Look off about twice that distance to Venus' upper left for Arcturus. Saturn's rings have widened to 10° from edge-on, and present an interesting sight along with its larger moons in a small telescope.

Of course, Jupiter shines almost as brilliantly as Venus during the evening, high in the south-southwest. The long-absent South Equatorial Belt continues to re-form, as dark markings spread east and west around the planet from a storm that broke out in the SEB's latitude about a month ago.

Uranus is still within 2° to the left of Jupiter, and can be spotted in a small telescope. Have a look at Jupiter first, and then look for an object to the upper left of Jupiter with about the same brightness as Ganymede. Ganymede is about magnitude 5.36 where Uranus is very slightly dimmer at about magnitude 5.45. Don't confuse Uranus with the star 20 Pisces (20 Psc,) which is also the same magnitude, but it is somewhat redder, and about halfway in between Jupiter and Uranus.

Neptune is much dimmer at magnitude 7.9, and is still up in the southwest in Capricornus after dark. Look for 5th-magnuitude Mu Capricorni next to it.
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Astronomy From Your Back Yard - 12/08 to 12/14 2010

By Dave Grosvold

  
If you can get out and observe in the two hours before the coming of dawn this week, Venus blazes in the southeast, even after sunrise. Venus is still at its highest luminosity, at magnitude –4.8 and nearly as high as it gets. Can you watch Venus past sunrise with your naked eye? Look for much fainter Spica to Venus' upper right (about 20°,) and for Saturn about 20° above Spica.

In the evenings this week, Mercury remains in view low about the southwest horizon during twilight. Look about 40 minutes after sunset. Mercury fades from magnitude –0.4 to +0.1 this week.

  
On Wednesday Dec 8th, by 7 or 8 PM CST, bright Capella in Auriga is high in the east-northeast. To its right in the east is the Pleiades (M45), or Seven Sisters, and below it is ruddy Aldebaran in Taurus. Below Capella lie Castor and Pollux, the heads of the twins of Gemini. It will be important to know the location of these twins early next week.

As soon as it gets dark on Thursday evening, look for the waxing crescent Moon in the southwest. To the right of the Moon about 7°, is tiny Alpha Capricorni (α Cap.) If you have sharp vision you can barely see that this is a very close double star. You can resolve it easily in binoculars.

Jupiter still shines brightly this week at magnitude -2.5. Just after dusk on Friday evening look far to the lower right of Jupiter for the waxing crescent Moon. Look below Jupiter to the lower left of the Moon for Fomalhaut (FOAM-a-lout), in Piscis Austrinus, sometimes called “the Autumn Star.”

By Saturday evening, the nearly first-quarter Moon this evening forms a roughly equilateral triangle with bright Jupiter to its upper left and Fomalhaut to its lower left. The Moon reaches First Quarter at 7:59 AM CST, on Monday December 13th.

  
Monday, December 13th near midnight marks the start of the peak of the Geminid meteor shower for this year, and for most observers, it is the highlight of the week. The peak of the shower continues through the night into the morning hours of Tuesday, December 14th. The name “Geminids” refers to the fact that the radiant for this meteor shower appears to come from the heart of the Twins of Gemini. When meteors are traced back to their apparent origin, the paths they followed all converge at a point on the sky known as the radiant.

From now until December 13th, hourly rates increase until a peak of 50-80 meteors per hour is attained. The rate then tapers off until the last Geminids on December 18th, when the rates fall to one every hour or so. Meteor showers occur all the time, but most are very weak. So there may be stray meteors that are not part of the Geminids during this time as well. When you see a meteor, how do you know if it's a Geminid? Trace the path of the meteor back to its apparent origin. If that origin ends up being in Gemini or close to it, then it's probably a Geminid.

The best way to observe the Geminid Meteor Shower is lie back on a chaise lounge with a clear view of the sky toward Gemini. This time of year, be sure to dress warmly, get a thermos of coffee or hot chocolate, and maybe even throw on a blanket or two. As you lie there, look high up and all around the sky, and don't focus in just one place.

  
Meteors will appear all over the sky, but the majority will appear to have come from the direction of Gemini, so we face the chaise lounge that way. But we scan from overhead down to about 30° up the sky. We also scan off to the right, and then to the left, looking at the big picture rather than focusing in any one area. Don't discount the sky opposite Gemini, either. Meteors can be seen all over the sky. See if you can count the number of meteors you see in an hour's time, and note the time of night.

On a historical note, the Geminid meteor shower appeared suddenly in the latter part of the 1800's. R. P. Greg of Manchester in the UK first noted several meteors that had a radiant in Gemini in December of 1862. Several other observers independently discovered the same activity the same year from the United States.

Early observations in the late nineteenth century reported the hourly rates at about 14 per hour. As the century waned, the hourly rate seemed to increase to about 23 per hour, with many more bright meteors. These rates have continued to increase throughout the 20th century, averaging about 50 per hour mid-century with the peak rate reaching an average of 80 per hour in the 1980s. The peak hourly rate continues to remain at 80 per hour today. Scientists now think the Geminids are tied to the passage of an asteroid (or minor planet,) 3200 Phaethon, in our solar system across Earth orbit every few years. The Earth passes through the dust and debris left in its wake, creating tiny meteors in our upper atmosphere as we pass.
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Blue Rings around Red Galaxies

NASA Space Placeby Trudy E. Bell and Dr. Tony Phillips

  
The Galaxy Evolution Explorer UV space telescope helped to identify red elliptical galaxies that also emitted the strongest UV. These are detailed, long-exposure Hubble Space Telescope images of four of these galaxies that capture the UV-emitting rings and arcs indicative of new star formation.
Click image for larger view
Beautiful flat rings around the planet Saturn are one thing — but flat rings around entire galaxies?

That is the astonishing discovery that two astronomers, Samir Salim of Indiana University at Bloomington and R. Michael Rich of UCLA described in the May 10, 2010, issue of The Astrophysical Journal Letters.

“For most of the twentieth century, astronomers observing at visible wavelengths saw that galaxies looked either ‘red and dead’ or ‘blue and new,’” explained Salim. Reddish galaxies were featureless, shaped mostly like balls or lentils; bluish ones were magnificent spirals or irregular galaxies.

Elliptical galaxies looked red, astronomers reasoned, because they had mostly old red giant stars near the end of their life cycles, and little gas from which new stars could form. Spiral and irregular galaxies looked blue, however, because they were rich in gas and dust that were active nurseries birthing hot, massive, bluish stars.

At least, that's how galaxies appear in visible light.

As early as the 1970s, though, the first space-borne telescopes sensitive to ultraviolet radiation (UV) revealed something mysterious: a few red elliptical galaxies emitted “a surprising ultraviolet excess,” said Rich. The observations suggested that some old red galaxies might not be as “dead” as previously supposed.

To investigate, Salim and Rich used NASA’s Galaxy Evolution Explorer satellite to identify 30 red elliptical galaxies that also emitted the strongest UV. Then they captured a long, detailed picture of each galaxy using the Hubble Space Telescope.

“Hubble revealed the answer,” says Salim. The UV radiation was emitted by enormous, flat bluish rings that completely surrounded each reddish galaxy, reminiscent of the rings of Saturn. In some cases, the bluish rings even showed a faint spiral structure!

Because the bluish UV rings looked like star-forming spiral arms and lay mostly beyond the red stars at the centers of the elliptical galaxies “we concluded that the bluish rings must be made of hot young stars,” Salim continued. “But if new stars are still being formed, that means the red-and-dead galaxies must have acquired some new gas to make them.”

How does a galaxy “acquire some gas?” Salim speculates that it was an act of theft. Sometimes galaxies have close encounters. If a gas-rich irregular galaxy passed close to a gas-poor elliptical galaxy, the gravity of the elliptical galaxy could steal some gas.

Further studies by Galaxy Evolution Explorer, Hubble and other telescopes are expected to reveal more about the process. One thing is certain, says Rich: “The evolution of galaxies is even more surprising and beautiful than we imagined.”

The press release is available at http://www.galex.caltech.edu/newsroom/glx2010-03f.html. The full published article is “Star Formation Signatures in Optically Quiescent Early-Type Galaxies” by Samir Salim and R. Michael Rich, The Astrophysical Journal Letters 714: L290–L294, 2010 May 10.

Point the kids to the Photon Pile-up Game at http://spaceplace.nasa.gov/en/kids/galex/photon, where they can have fun learning about the particle nature of light.

This article was provided by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration.
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Help Juno cut through Jupiter’s veil

NASA Space Place
  
Hey kids! The roman god Jupiter (for whom the planet is named) drew a veil of clouds around himself to hide his mischief. Jupiter's wife, the goddess Juno, had the power to peer through the clouds and see Jupiter’s true nature. NASA’s Juno spacecraft, to be launched next summer, will also look beneath the clouds to reveal Jupiter’s mysteries. Get a Juno-view of Jupiter by playing the exciting new JunoQuest game at The Space Place, http://spaceplace.jpl.nasa.gov/en/kids/juno.
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Astronomy From Your Back Yard - 12/01 to 12/07 2010

By Dave Grosvold

  
     
  
On Friday morning, about 1/2 hour before dawn, look for a razor-thin crescent Moon far below Venus in the southeastern sky. Venus is at its maximum brightness magnitude –4.9, and as is commonly known as the “Morning Star”. Far above Venus is Spica in Virgo, and above that, Saturn at magnitude +0.9. Saturn's rings are 9° or 10° from edge-on now, and early dawn is the best time to observe the ringed planet all this week.

  
Early in the evening all week, the constellation Cassiopeia floats very nearly directly overhead when you face north. Look for an M-shaped grouping of stars high above you for Cassiopeia. About halfway from Cassiopeia to the horizon lies Polaris, the North Star. Polaris is the brightest star in the otherwise dim constellation of Ursa Minor, commonly known as the Little Dipper.

Far below Polaris, and very nearly below the horizon, lie the upper-most stars of the Big Dipper asterism, part of the constellation of Ursa Major. The tail of Draco wends its way between Polaris and the stars of Ursa Major. This far south, you may not even be able to spot the stars of Ursa Major without finding a nearly flat horizon clear of obstructions.

Jupiter shines high in the south to southwest during evening, the brightest star-like point in the evening sky. Jupiter's missing South Equatorial Belt is finally starting to re-group, becoming barely visible as dark material spreads from a series of telltale bright storm spots that appeared three weeks ago.

On Friday evening, Jupiter's moon Europa reappears from eclipse out of Jupiter's shadow around 7:30 PM CST. Watch and wait for a few minutes, and a small telescope will show it gradually become visible just east of the planet.

  
Later in the evening, look to the east to see the starry harbingers of Winter, orange Aldebaran in Taurus, fiery red Betelgeuse and blue-white Rigel in Orion, bright yellow Capella in Auriga, the TwinsCastor and Pollux in Gemini, brilliant blue-white Sirius, the brightest star in the sky — and the brightest in Canis Major. Don't forget the white binary star system Procyon in Canis Minor, considered the seventh brightest in the sky. Betelgeuse, Sirius, and Procyon make the three vertices of the Winter Triangle asterism.

Mercury, at magnitude –0.4 is now at the best time for observing its current evening apparition. Still, it's quite low on the horizon, and a challenge. Look for it in mid-twilight just above the southwest horizon.

New Moon occurs on Sunday, December 5th at 11:36 AM CST, so both Saturday evening and Sunday evening will be good times to observe deep-sky objects (those outside our Solar System.)

This week is a great time to see Iridium Flares, both in the morning and evening. At 6:02 PM CST on Sunday, December 5th, Iridium 63 flares to magnitude -0 low in the western sky at an altitude of 11°. Just a few minutes later at 6:37 PM CST, Iridium 49 flares to magnitude -2 at an altitude of 30° in the south. Early Monday morning, at 7:01 AM CST, Iridium 46 flares to an absolutely brilliant -8 magnitude high up in the sky at 71° altitude. Look for it at azimuth 339° (in the NNW.) This is the brightest flare that will occur over the coming week.

Monday evening, Iridium 65 and 66 put on a show at 5:47 PM and 5:56 PM CST, respectively. Iridium 65 will flare to magnitude -1 and Iridium 66 will reach magnitude -2. Both satellites will be low (at altitudes of 13° and 10°) in the Western sky. On Tuesday morning at 6:55 AM CST, we see Iridium 46 reach a fairly bright magnitude -5, pretty high up at an altitude of 69° in the NNW, and then Tuesday evening at 5:41 PM CST, Iridium 68 also flares to magnitude -5 low at an altitude of 14° in the Western sky. You can find out more about these at the Heavens Above web site.
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Astronomy From Your Back Yard - 11/17 to 11/23 2010

By Dave Grosvold

  
Unfortunately, business travel demands have kept me away from this column for a couple of weeks. It's good to be back! Well, it looks like there will be some clear skies and great opportunities for night-time sky watching Thursday through Sunday this week. To get a better idea how the night sky viewing will be for the next two evenings, check out the Fort Smith Clear Sky Chart. This chart will tell you how dark the sky will be, when you can expect cloud cover during the night, and what transparency and seeing conditions are expected.

  
On Wednesday evening, Jupiter will be slightly higher and about 20° to the right of the waxing gibbous Moon. The Moon reaches the Full phase on Sunday, November 21 at 11:28 AM CST. As a result, it will be a bright beacon in the night sky all week, washing out all but the brightest stars and planets. There will be early-morning dark skies late this week (Thursday & Friday,) as the Moon sets at about 3:00 AM CST on Thursday morning, setting about an hour later each morning until later in the week when it remains visible the entire night.

The bright star Vega in the constellation Lyra remains the brightest star in the west-northwest these evenings. The brightest star higher above it is Deneb in the constellation Cygnus. To the left of Vega lies the third member of the Summer Triangle, Altair, in the constellation Aquila. Both the cool crisp air and the Summer Triangle low in the western sky are sure signs of approaching winter.

For a challenge this week, use binoculars to scan for Mercury very low in the southwest less than a half hour after sunset. Mars is less than 2° to Mercury's upper right. If you place Mercury in the lower left of the field of view, you should be able to detect fainter Mars above and to the right.

By 9:00 PM CST Saturday, November 20th, the constellation Orion has risen in the east-southeast. Look for it far below this evening's high, bright Moon. The three unmistakable belt stars in Orion will be lined up vertically, with the bright blue-white star Rigel on the right, and fiery-red Betelgeuse on the left.

  
Halfway between Betelgeuse and the Moon is another bright red star, Aldebaran, in Taurus. Draw an imaginary line from the Moon down through Aldebaran to Betelgeuse, and then imagine a line perpendicular to the first one, to the left of Adebaran you should see the bright yellow star Capella, in the constellation Auriga.

  
On Sunday evening, the Full Moon passes just below the Pleiades (M-45,) an open cluster in the constellation Taurus. At closest approach the Moon is just slightly more than 4° from the center of the Pleiades, or just over the width of two fingers held at arm's length.

This week, Venus is rising ever higher at dawn in the east-southeast. Look a little above it or to its upper right for much-fainter Spica in Virgo. Look higher (about 16°) above it for Saturn. Saturn's rings have widened to a tilt of about 9° from edge-on. The best time for observing Saturn with a telescope is about an hour before sunrise, or about 6:00 AM local time, when the planet will be above the “muck” -- the haze and turbulence found close to the horizon.

You may also be able to catch a couple of bright Iridium Flares this week. Iridium 41 flares to -6 magnitude at 4:51 AM CST on Thursday morning. Look for it in the south at an altitude of 21°. Then on Sunday evening at 5:58 PM CST, you can catch Iridium 66 flare to magnitude -7 in the south at an altitude of 33°. Early on Monday morning, Iridium 62 flares to magnitude -4 nearly overhead at an altitude of 59° in the north-northwest. There are a several other chances to catch Iridium Flares, this week albeit at dimmer magnitudes. Be sure to check the web site at Heavens Above for times and positions.

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