Terry's Astronomy Thread.

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Re: Terry's Astronomy Thread.

What's in the sky tonight?
November 24, 2013

-During dawn Monday and Tuesday mornings, when you're preparing to use binoculars or a telescope to make one last pre-perihelion try for Comet ISON barely above the bright horizon, you'll find Mercury and fainter Saturn shining to the naked eye just 3/4° apart (at the times of dawn in North America). They're well above the spot to look for the comet: by 7° on Monday, 9° on Tuesday.

-In a telescope, Mercury will be a tiny, slightly gibbous disk 5.6 arcseconds in diameter (no bigger than Mars, high in the southeast), while Saturn is dimmer but much larger: 34″ across its rings. They're a nice consolation prize!

-NASA's STEREO-A spacecraft is monitoring Comet ISON as it approaches the sun for a close encounter on Nov. 28th. The latest movie from the spacecraft's Heliospheric Imager captures not only Comet ISON but also Earth, Mercury, and Comet Encke. In the movie, which spans a two day period from Nov. 19 to Nov. 22, the sun is to the right, off-screen. "The dark 'clouds' coming from that direction are density enhancements in the solar wind, and these are what are causing the ripples you see in the comet tails," explains Karl Battams of NASA's Comet ISON Observing Campaign.

Although the two comets seem to be experiencing the same solar wind, their tails ripple differently. "Encke has kind of long waves in the tail, whereas ISON's seems almost like high-frequency puffs," points out Battams.

Appearances notwithstanding, the two comets might be in two different streams of solar wind. "The most likely explanation is that ISON is in a faster stream," he comntinues. "Imagine holding a flag on a slightly breezy day. The flag will waft gently in the breeze. Now imagine holding it in really strong winds. The flag will be rippling violently, but those ripples will be smaller in amplitude."

Astro Picture of the Day:
November 24, 2013

Source:
Comet Hale-Bopp, the Great Comet of 1997, was quite a sight. In the above photograph taken on 1997 April 6, Comet Hale-Bopp was imaged from the Indian Cove Campground in the Joshua Tree National Park in California, USA. A flashlight was used to momentarily illuminate foreground rocks in this six minute exposure. An impressive blue ion tail was visible above a sunlight-reflecting white dust tail. Comet Hale-Bopp remained visible to the unaided eye for over a year before returning to the outer Solar System and fading. As Comet ISON approaches the Sun this week, sky enthusiasts around the Earth are waiting to see if its tails will become even more spectacular than those displayed by Comet Hale-Bopp.

[Bluearrowll]

Re: Terry's Astronomy Thread.

What's in the sky tonight?
November 25, 2013

-Last-quarter Moon (exact at 2:28 p.m. EST). The Moon rises around 1 a.m. tonight. By dawn Tuesday morning it's high in the south, with Regulus to its right and Mars to its lower left.

-As Comet ISON approaches the sun, it is becoming increasingly difficult for observers on Earth to photograph the comet. Indeed, by Nov. 24th it seemed impossible. But it only seemed that way. Working from a high-altitude site in the Canary islands, Juan Carlos Casado successfully imaged Comet ISON on Sunday morning deep inside the rosy glow of dawn. "I took this picture of Comet ISON on Nov. 24th at 6: 25 UT from the Teide Observatory," says Casado. "The comet was over the distant island of Gran Canaria above a sea of clouds about 1 hour before sunrise and only 16° from the sun. The exceptional atmospheric conditions of Teide Observatory allowed me to capture the image."

Astro Picture of the Day:
November 25, 2013

Source:
How far away is spiral galaxy NGC 4921? Although presently estimated to be about 310 million light years distant, a more precise determination could be coupled with its known recession speed to help humanity better calibrate the expansion rate of the entire visible universe. Toward this goal, several images were taken by the Hubble Space Telescope in order to help identify key stellar distance markers known as Cepheid variable stars. Since NGC 4921 is a member of the Coma Cluster of Galaxies, refining its distance would also allow a better distance determination to one of the largest nearby clusters in the local universe. The magnificent spiral NGC 4921 has been informally dubbed anemic because of its low rate of star formation and low surface brightness. Visible in the above image are, from the center, a bright nucleus, a bright central bar, a prominent ring of dark dust, blue clusters of recently formed stars, several smaller companion galaxies, unrelated galaxies in the far distant universe, and unrelated stars in our Milky Way Galaxy.

[Bluearrowll]

Re: Terry's Astronomy Thread.

What's in the sky tonight?
November 26, 2013

-Jupiter's Great Red Spot should cross the planet's central meridian around 11:36 p.m. Eastern Standard Time tonight. The tiny black shadow of Jupiter's moon Io crosses the planet's face from 11:47 p.m. EST to 2:01 a.m. EST.

-By about 2 a.m. Wednesday morning the waning Moon is up in the east with Mars shining to its left. By dawn Wednesday morning, they're high in the southeast.

-Comet ISON is getting all the press, but there is a second comet near the sun as well: Comet Encke. NASA's STEREO-A spacecraft is monitoring both. Click to view an updated movie of the solar wind buffeting two comets. In the movie, which spans a three+ day period from Nov. 20 to Nov. 23, the sun is to the right, off-screen. At first glance, Earth and Mercury appear to be labeled backwards. The strange arrangement is actually correct. This is how the two planets appear from STEREO-A's vantage point over the farside of the sun.

"The dark 'clouds' moving from left to right are density enhancements in the solar wind, and these are what are causing the ripples you see in the comet tails," explains Karl Battams of NASA's Comet ISON Observing Campaign.

The ripples could become even more dramatic if a CME hits the comets. This is Comet ISON's first visit to the sun, but Comet Encke has been here before. In 2007 a CME hit Encke and ripped off its tail. Battams and other researchers hope something similar is about to happen now. "I'd love to see a big CME hit Comet ISON," he says in a story from Science@NASA. Watching the impact could teach researchers new things about CMEs and comets.

Astro Picture of the Day:
November 26, 2013

Source:
One might say this was a bell weather day for the Sierra Nevada mountains. In January, just as the Sun was setting above the district of Albayzín in Grenada, Spain, a huge cloud appeared as a bell capping the Veleta peak. Such a Cap cloud is formed by air forced upwards by a mountain peak, with the air then cooling, saturating with moisture, and finally having its molecular water condense into cloud droplets. Such a bell-shaped cloud structure is unusual as air typically moves horizontally, making most clouds nearly flat across at the bottom. Vertical waves can also give additional lenticular cloud layers, as also seen above. Given the fleeting extent of the great cloud coupled with momentarily excellent sunset coloring, one might considered this also a bellwether day for an accomplished photographer.

[Bluearrowll]

Re: Terry's Astronomy Thread.

What's in the sky tonight?
November 27, 2013

-The Earthside of the sun is quiet. NOAA forecasters estimate a slim 1% chance of either M- or X-class solar flares on Nov. 27th. However, there is at least one active region on the farside of the sun which could target Comet ISON when it swings around the farside after Nov. 28th.

-Comet ISON is hurtling toward the sun today at 240,000 mph and, despite the rising heat, the comet appears to be intact. Yesterday, reports of fading spectral lines from the comet's core raised concerns that the icy nucleus might be disintegrating. Current images from NASA and ESA spacecraft, however, show the comet still going strong. Comet ISON has just entered the field of view of the Solar and Heliospheric Observatory (SOHO).

-The comet's entrance coincides with a bright CME racing away from the sun's southwestern limb. Astronomers have been wondering what might happen if a CME strikes Comet ISON. This CME, however, will probably miss. The source of the cloud is a farside active region, which is not directly facing the comet.

-Astronomer Karl Battams of NASA's Comet ISON Observing Campaign urges readers to remember the following: "Comet ISON is a dynamically new sungrazing comet, fresh in from the Oort Cloud, and the last time we saw an object like this was never! Furthermore, a sungrazing comet just days from perihelion has never been studied in this kind of detail - we're breaking new ground! When we factor in your standard 'comets are unpredictable' disclaimer, what we have is a huge recipe for the unknown."

Significant ISON Satellite Dates:
• Nov. 21–28: STEREO-A, Heliospheric Imager.
• Nov. 26–29: STEREO-B, coronagraphs. Stereo-B will be the only craft to watch ISON transit the face of the Sun.
• Nov. 27–30: SOHO, coronagraphs.
• Nov. 28–29: STEREO-A, coronagraphs.
• Nov. 28: Solar Dynamics Observatory (SDO); for about 3 hours around perihelion.
• Nov. 28: Japan's Hinode, X-Ray Telescope; for about 55 minutes around perihelion.

Astro Picture of the Day:
November 27, 2013

Source:
Will Comet ISON survive tomorrow's close encounter with the Sun? Approaching to within a solar diameter of the Sun's surface, the fate of one of the most unusual comets of modern times will finally be determined. The comet could shed a great amount of ice and dust into a developing tail - or break apart completely. Unfortunately, the closer Comet ISON gets to the Sun, the harder it has been for conventional telescopes to see the brightening comet in the glare of the morning Sun. Pictured in the above short time lapse video, Comet ISON was captured rising over the Canary Islands just above the morning Sun a few days ago. If the comet's nucleus survives, the coma and the tails it sheds might well be visible rising ahead of the Sun in the next few days or weeks. Alternatively, satellites watching the Sun might document one of the larger comet disintegrations yet recorded. Stay tuned!

[Bluearrowll]

Re: Terry's Astronomy Thread.

What's in the sky tonight?
November 28, 2013

-Comet ISON is brightening rapidly as it plunges into the sun's atmosphere. At closest approach around 1:45 p.m. EST on Nov. 28th (Thanksgiving Day in the USA), the comet will be little more than a million kilometers above the sun's fiery surface. Temperatures around ISON's icy nucleus could rise as high as 5000o F. No one knows if it can survive that kind of baking--but if it does, it could emerge as a splendid naked-eye comet in early December.

Right now, the best views of the comet are coming from the Solar and Heliospheric Observatory (SOHO). Over the course of the animation, Comet ISON brightens by a factor of at least four, and possibly as much as a factor of 10. It easily outshines the 1st-magnitude red giant star Antares to the lower left of the sun.

Researchers have been wondering what might happen if a CME strikes Comet ISON. They might find out before the day is over. As the movie shows, CMEs are billowing away from the sun in all directions. Avoiding a collision will become increasingly difficult as the comet moves closer to active regions on the sun's surface.

During the hours around closest approach, NASA's Solar Dynamics Observatory (SDO) will take high-resolution pictures of the comet flying through the sun's atmosphere. This diagram below illustrates the sequence of events. Usually, SDO points straight at the sun. In this case, however, the observatory is being offset and moved three times to track the speeding comet. SDO images of sungrazing Comet Lovejoy in Dec. 2011 were dramatic. Comet ISON could be even better.

Astro Picture of the Day:
November 28, 2013

Source:
South of the large star-forming region known as the Orion Nebula, lies bright blue reflection nebula NGC 1999. At the edge of the Orion molecular cloud complex some 1,500 light-years distant, NGC 1999's illumination is provided by the embedded variable star V380 Orionis. That nebula is marked with a dark sideways T-shape near center in this cosmic vista that spans about 10 light-years. The dark shape was once assumed to be an obscuring dust cloud seen in silhouette against the bright reflection nebula. But recent infrared images indicate the shape is likely a hole blown through the nebula itself by energetic young stars. In fact, this region abounds with energetic young stars producing jets and outflows with luminous shock waves. Cataloged as Herbig-Haro (HH) objects, named for astronomers George Herbig and Guillermo Haro, the shocks look like red gashes in this scene that includes HH1 and HH2 just below NGC 1999. The stellar jets push through the surrounding material at speeds of hundreds of kilometers per second.

[Bluearrowll]

Re: Terry's Astronomy Thread.

For a brief couple hours, live NASA coverage of Comet ISON.

[Bluearrowll]

Re: Terry's Astronomy Thread.

What's in the sky tonight?
November 29, 2013

-Cancel the funeral. Comet ISON is back from the dead. Yesterday, Nov. 28th, Comet ISON flew through the sun's atmosphere and appeared to disintegrate before the cameras of several NASA and ESA spacecraft. This prompted reports of the comet's demise. Today, the comet has revived and is rapidly brightening.

-Before the flyby, experts had made many predictions about what might happen to the comet, ranging from utter disintegration to glorious survival. No one predicted both.

Karl Battams of NASA's Comet ISON Observing Campaign says, "[colleague] Matthew Knight and I are ripping our hair out right now as we know that so many people in the public, the media and in science teams want to know what's happened. We'd love to know that too! Right now, here's our working hypothesis:

"As comet ISON plunged towards to the Sun, it began to fall apart, losing not giant fragments but at least a lot of reasonably sized chunks. There's evidence of very large dust in the long thin tail we saw in the [SOHO coronagraph] images. Then, as ISON plunged through the corona, it continued to fall apart and vaporize, losing its coma and tail completely just like sungrazing Comet Lovejoy did in 2011. What emerged from the Sun was a small but perhaps somewhat coherent nucleus that has resumed emitting dust and gas for at least the time being."

Battams emphasizes that it is too soon to tell how big the remnant nucleus is or how bright the resurgent comet will ultimately become. "We have a whole new set of unknowns, and this ridiculous, crazy, dynamic and unpredictable object continues to amaze, astound and confuse us to no end. We ask that you please be patient with us for a couple of days as we analyze the data and try to work out what is happening."

Astrophotographer Babak Tafreshi has edited an HD video that compares views of ISON from both of SOHO's coronagraphs. "It seems the comet could become a naked eye object with several degrees of scattered tail by Dec 2nd or 3rd," he predicts. "It's not the comet of the century for sure, and fainter than the Lovejoy sungrazer in Dec. 2011, but an interesting imaging target is just a few nights away!" His video can be found here; http://vimeo.com/80568171

Astro Picture of the Day:
November 29, 2013

Source:
Sungrazing Comet ISON reached perihelion, its closest approach to the Sun, yesterday, November 28, at 18:45 UT. The comet passed just over 1 million kilometers above the solar surface, a distance less than the diameter of the Sun. These two panels follow ISON before (right) and after its close approach, imaged by the LASCO instrument onboard the Sun staring SOHO spacecraft. Overwhelming sunlight is blocked by LASCO's central occulting disk with a white circle indicating the Sun's positon and scale. The bright comet is seen along its path at the bottom of the before panel, but something much fainter exits near the top of the after panel, potentially a dust tail reforming from the debris left from ISON's perihelion passage.




Latest ISON Image

[Bluearrowll]

Re: Terry's Astronomy Thread.

What's in the sky tonight?
November 30, 2013

-A bright CME (coronal mass ejection) blasted away from the farside of the sun during the early hours of Nov. 30th. Although the cloud appears to overrun the comet in movies from SOHO (watch), in fact it probably missed or delivered no more than a glancing blow. That's too bad, because a CME impact could reveal the true nature of Comet ISON's mysterious undead core.

-Comet ISON continues to do the exact opposite of what scientists have forecasted it to do. At 19:54 UT Filip Fratev (Bulgarian Acadamy of Sciences) wrote, "ISON [has] started to fade.... [In] the last four hours it faded by more than 2 magnitudes and obviously is less bright... I estimated the comet to be between 2.6 and 3.1 magnitude now."

Four hours later Karl Battams of the Comet ISON Observing Campaign tweeted, "We can't tell if #ISON is in one piece or many. It's about mag 5 now and fading."

-Which rises first: bright Jupiter in the east-northeast, or bright Rigel in Orion's foot in the east-southeast? Both are up by about 8 p.m. depending on where you live. At the latitudes of the U.S. and southern Canada, Rigel comes first tonight. As far north as Paris (latitude 49°) and points farther north, Jupiter is first.

Astro Picture of the Day:
November 30, 2013

Source:
After failing to appear for Sun staring spacecraft at perihelion, its harrowing closest approach to the Sun, sungrazing Comet ISON was presumed lost. But ISON surprised observers yesterday as material still traveling along the comet's trajectory became visible and even developed an extensive fan-shaped dust tail. Edited and processed to HD format, this video (vimeo, youtube) is composed of frames from the SOHO spacecraft's coronographs. It follows the comet in view of the wide (blue tint) and narrow (red tint) field cameras in the hours both before and after perihelion passage. In both fields, overwhelming sunlight is blocked by a central occulting disk. A white circle indicates the Sun's positon and scale. With questions to be answered and the tantalizing possibility that a small cometary nucleus has survived in whole or part, surprising comet ISON will be rising before dawn in planet Earth's skies in the coming days.

[Bluearrowll]

Re: Terry's Astronomy Thread.

What's in the sky tonight?
December 1, 2013

-NOAA forecasters estimate a 25% chance of polar geomagnetic storms on Dec. 2nd when a CME might deliver a glancing blow to Earth's magnetic field. High-latitude sky watchers should be alert for auroras.

-John Bortle withdraws his relatively optimistic forecast posted yesterday. He writes,

The comet's appearance only suggests a progressive decline now.
While ISON's photometric behavior up to and around perihelion did seem to mimic that of 1962's impressive Comet Seki-Lines, the failure of ISON's current cloud-like coma to exhibit any area of condensation as the cloud thins, and its fading and growing diffuseness, do not correspond to Seki-Lines' post-perihelion regeneration....

To be similar in behavior with C/Seki-Lines, ISON would be developing an increasingly small, dense, very bright condensation within the coma. Likewise, the intensity and length of the tail(s) would be rapidly growing, just as we saw in the case of 2011 W3 Lovejoy following its perihelion....

Following a 2- to 4-day blind period after the comet leaves spacecraft view, Bortle expects only a "large, low-surface-brightness, diffuse cloud showing just a trace of tail" — in other words a challenge object for skilled astrophotographers and image processers, not visual observers — if anything at all.

-Comet ISON is fading fast as it recedes from the sun. Whatever piece of the comet briefly survived its Thanksgiving Day brush with solar fire is now dissipating in a cloud of dust.

This development makes it unlikely that Comet ISON will put on a good show after it exits the glare of the sun in early December. Experienced astrophotographers might be able to capture the comet's fading "ghost" in the pre-dawn sky, but a naked-eye spectacle is out of the question.

On Nov. 29th, pilot Brian Whittaker tried to catch a first glimpse of Comet ISON from Earth, post-perihelion, from a plane flying 36,000 feet over the Arctic Circle in northern Canada. No luck.

"Ideal viewing conditions from the Arctic revealed no Comet ISON," reports Whittaker. "This negative report is to quench the thirst of other fellow dreamers under cloudy skies or further south. Later I could see that SOHO showed the comet dimming further."

Despite Whittaker's negative result, it is too soon to rule out observations from Earth as the twice-dead comet moves away from the glare of the sun. Meanwhile, NASA's fleet of solar observatory will be tracking the remains. Stay tuned for more images.

Astro Picture of the Day:
December 1, 2013

Source:
Why are these people shooting a powerful laser into the center of our Galaxy? Fortunately, this is not meant to be the first step in a Galactic war. Rather, astronomers at the Very Large Telescope (VLT) site in Chile are trying to measure the distortions of Earth's ever changing atmosphere. Constant imaging of high-altitude atoms excited by the laser -- which appear like an artificial star -- allow astronomers to instantly measure atmospheric blurring. This information is fed back to a VLT telescope mirror which is then slightly deformed to minimize this blurring. In this case, a VLT was observing our Galaxy's center, and so Earth's atmospheric blurring in that direction was needed. As for inter-galaxy warfare, when viewed from our Galaxy's center, no casualties are expected. In fact, the light from this powerful laser would combine with light from our Sun to together appear only as bright as a faint and distant star.

[Bluearrowll]

Re: Terry's Astronomy Thread.

What's in the sky tonight?
December 2, 2013

-Mars is passing 1.2° upper left of the 3.6-magnitude star Beta Virginis before dawn this morning and tomorrow morning — a sidelight from the Comet ISON hunt. Look for Mars shining very high in the southeast before dawn gets too bright.

-Following its Thanksgiving Day brush with solar fire, sundiving Comet ISON is now just a cloud of dust. Among experts, a consensus is building that the comet broke apart shortly before perihelion (closest approach to the sun). In the movie, note how rapidly the comet fades just before it vanishes behind the occulting disk of the SOHO coronagraph.

-After perihelion, the comet emerges as a diffuse remnant of its former self. No one knows for sure what is inside that fan-shaped cloud. Possibilities include a small remnant nucleus or a "rubble pile" of furiously vaporizing fragments. By the end of the day on Nov. 28th, Comet ISON was spent.

As of Dec. 2nd, the cloud of debris is no brighter than a star of approximately 8th magnitude. Experienced astrophotographers might be able to capture the comet's fading "ghost" in the pre-dawn sky of early December, but a naked-eye spectacle is out of the question.

-China is about to join the club of nations that have landed on the Moon. On Dec. 1st, China's Chang'e-3 spacecraft blasted off from the Sichuan province in southwest China. It's payload: a six-wheeled, 260-lb rover named the "Jade Rabbit" ("Yutu" in Chinese), which could touch down on the lunar surface as early as Dec. 14th.

-Unlike the soft landings of unmanned spacecraft from the USA and the Soviet Union, Chang'e-3 will be able to survey the landscape first and determine the safest spot. The most likely destination is Sinus Iridum, the Bay of Rainbows.

A Chinese-made nuclear battery will power the rover after it lands on the lunar surface. Using plutonium-238, the battery will last for more than 30 years. The rover also has expandable solar arrays to absorb the sun’s energy during the day and retract at night to cover and protect equipment from temperatures of minus 170 degrees Celsius. Onboard sensors include a ground-probing radar, cameras, and a soil sampler.

Jade Rabbit's name comes a Chinese myth: According to the ancient story, a lady called Chang'e swallowed magic pills, which allowed her to fly to the Moon along with her pet rabbit "Yutu". There she became a goddess, and has been living on the Moon with the white rabbit ever since.

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Astro Picture of the Day:
December 2, 2013

Source:
Comet Lovejoy was captured last week passing well in front of spiral galaxy M63. Discovered only three months ago and currently near its maximum brightness, Comet Lovejoy can be seen near the Big Dipper from dark northerly locations before dawn with the unaided eye. An unexpected rival to Comet ISON, C/2013 R1 (Lovejoy), pictured above, is currently sporting a large green coma and a beautifully textured ion tail. Comet Lovejoy is now headed back to the outer Solar System but should remain a good sight in binoculars for another few weeks. Conversely, spiral galaxy M63, lies far in the distance and is expected to remain stationary on the sky and hold its relative brightness for at least the next few million years.

[Bluearrowll]

Re: Terry's Astronomy Thread.

What's in the sky tonight?
December 3, 2013

-With no sunspots actively flaring, the Earthside of the sun is quiet. However, two sunspots (AR1908 and AR1909) have 'beta-gamma' magnetic fields that harbor energy for moderately strong eruptions. NOAA forecasters estimate a 25% chance of M-class solar flares on Dec. 3rd.

-The Summer Triangle is still high after dusk in December. Spot Vega, its brightest star, in the west-northwest. The brightest above Vega is Deneb. Look farther to Vega's right for Altair.

-At the end of American Thanksgiving Day when the sun was setting over Sumterville, Florida, Paula Phillips took a break from her meal, stepped outside and saw something odd-a pair of luminous 'Vs' in the deepening twilight.

"I've never seen anything like this before," says Phillips. "I photographed the phenomenon with a simple small Samsung camera."

They're sun halos, caused by sunlight shining through ice crystals. Atmospheric optics expert Les Cowley explains:

"These two ‘V’ shaped halos, one rare and one common, change shape dramatically as the sun climbs," he says. "Near sunrise or sunset is the only time to catch them like this. The lower ‘V’ is an upper tangent arc from horizontal hexagonal prisms of ice. The upper one is a rare sunvex Parry arc from similar crystals that - strangely – are fixed so that two prism faces are always horizontal. In the full-sized image, we also see just a trace of a 22o halo and stretching upwards from the sun a sun pillar."

"I find it odd that I saw this in Florida!" continues Phillips. Yet Florida has ice crystal, too. The atmosphere 5 to 10 km above the Sunshine State is always cold enough for water to freeze.

"Florida and other warm places get plenty of halos-some of them exceedingly rare," says Cowley. "Look for them everywhere, winter and summer."

Astro Picture of the Day:
December 3, 2013

Source:
The many spectacular colors of the Rho Ophiuchi (oh'-fee-yu-kee) clouds highlight the many processes that occur there. The blue regions shine primarily by reflected light. Blue light from the star Rho Ophiuchi and nearby stars reflects more efficiently off this portion of the nebula than red light. The Earth's daytime sky appears blue for the same reason. The red and yellow regions shine primarily because of emission from the nebula's atomic and molecular gas. Light from nearby blue stars - more energetic than the bright star Antares - knocks electrons away from the gas, which then shines when the electrons recombine with the gas. The dark brown regions are caused by dust grains - born in young stellar atmospheres - which effectively block light emitted behind them. The Rho Ophiuchi star clouds, well in front of the globular cluster M4 visible above on lower left, are even more colorful than humans can see - the clouds emits light in every wavelength band from the radio to the gamma-ray.

[Bluearrowll]

Re: Terry's Astronomy Thread.

What's in the sky tonight?
December 4, 2013

-The sun's southern hemisphere is peppered with sunspots, but none of them is actively flaring. Solar activity remains low. NOAA forecasters estimate a 25% chance of M-class solar flares and a scant 1% chance of X-flares on Dec. 4th.

-Look for the waxing crescent Moon far lower right of Venus in twilight, as shown here.

-Watch Jupiter's moon Io gradually disappear into eclipse by Jupiter's shadow, just off the planet's western limb, around 10:58 p.m. EST. A small telescope is all you need.

-Earth is entering a stream of debris from rock comet 3200 Phaethon, source of the annual Geminid meteor shower. Our planet is just dipping into the outskirts of the debris zone now, so visual meteor rates are low. Nevertheless, the Canadian Meteor Orbit Radar (CMOR) is starting to pick up echoes from Geminid meteoroids. This Dec. 4th radar map shows a concentration of activity in the constellation Gemini.

"The Geminids, still ten days from their maximum, are very clearly visible in the latest CMOR data," reports Prof. Peter Brown of the University of Western Ontario, which operates the radar.

In the radar map, the Geminid radiant is labeled 'GEM.' A second nearby radiant labeled 'NOO' marks the location of the November omega Orionids, a minor shower that peaks in early December.

The Geminids won't peak until Dec. 13-14 when Earth passes through the core of the debris stream, but Brown thinks observers should start looking now. "Glare from the nearly-full Moon will interfere with the Geminid's maximum in mid-December," he says. "This week, however, the Moon is new. Observers should be starting to see activity from this very strong shower." Observing tip: The best time to look is during the hours between midnight and dawn when the constellation Gemini is high in the sky.

So what REALLY happened to Comet ISON?

Data from more distant STEREO cameras has now reached Earth and has been processed by NASA. The result is a view never before seen on this thread that might be of interest to the group.

http://www.planetary.org/blogs/emily-lakdawalla/2013/12021624-multiple-views-of-comet-ison.html

The blog above gives excellent detail about the science behind Comet ISON's constant dimmings and brightenings. And it all has to do with phase angle. Take a look at the latest videos from STEREO A and B. Notice how much slower Comet ISON looks on STEREO B: This is because the comet is speeding towards STEREO B almost head on.

Astro Picture of the Day:
December 4, 2013

Source:
This new comet is quite photogenic. Comet Lovejoy, discovered only three months ago, was imaged through ruins of ancient Mörby Castle in Sweden last week sporting a green-glowing coma and tails trailing several degrees. The past few weeks have been an unusually active time for comet watchers as four comets were visible simultaneously with binoculars: ISON, Lovejoy, Encke, and LINEAR. C/2013 R1 (Lovejoy) comet is currently visible to the unaided eye from a dark location. As Monday's new Moon will provide little glare, the next few days provide a good time to see Comet Lovejoy as it reaches its peak brightness. In two and a half weeks, Comet Lovejoy will reach its closest approach to the Sun at a distance just inside the orbital distance of the Earth.

[Bluearrowll]

Re: Terry's Astronomy Thread.

What's in the sky tonight?
December 5, 2013

-The crescent Moon poses about 7° to Venus's upper right in twilight, as shown here. As the sky darkens, look with binoculars for Alpha and Beta Capricorni to the Moon's upper left. Both are double stars for binoculars: Alpha is very easy to resolve, Beta is harder.

-When the sun goes down tonight, step outside and look southwest. The crescent Moon and Venus are converging for a beautiful close encounter. These are the two brightest objects in the night sky and they pop out of the twilight long before the sky fades to black. Erwin Matys and Karoline Mrazek of Project Nightflight photographed the pair converging over the Canary island El Hierro on Dec. 4th.

They'll be even closer together tonight. With less than 10o of arc seperating the two, they would fit together inside the bowl of the Big Dipper.

If you have binoculars or a small telescope, take a closer look at the heavenly bodies. Both are crescents. Like the Moon, Venus has phases and tonight it is 27% illuminated. For comparison, the lunar crescent is half as wide, about 13.5%.

Bonus: This week Venus is at its brightest for 2013, shining almost 200 times brighter than a 1st-magnitude star. That's why it is so easy to see before darkness falls. Look southwest as soon as the sun sets.

Astro Picture of the Day:
December 5, 2013

Source:
Very faint planetary nebula Abell 7 is some 1,800 light-years distant, just south of Orion in planet Earth's skies in the constellation Lepus, The Hare. Surrounded by Milky Way stars and near the line-of-sight to distant background galaxies, its generally simple spherical shape, about 8 light-years in diameter, is outlined in this deep telescopic image. Within its confines are beautiful, more complex details enhanced by the use of narrowband filters. Emission from hydrogen and nitrogen is shown in reddish hues with oxygen emission mapped to a bluish-green color, giving Abell 7 a more natural appearance that would otherwise be much too faint to be appreciated by eye. A planetary nebula represents a very brief final phase in stellar evolution that our own Sun will experience 5 billion years hence, as the nebula's central, once sun-like star shrugs off its outer layers. Abell 7 itself is estimated to be 20,000 years old. Its central star is seen here as a fading white dwarf some 10 billion years old.

[Bluearrowll]

Re: Terry's Astronomy Thread.

What's in the sky tonight?
December 6, 2013

-The waxing crescent Moon hangs high over Venus at dusk, with Alpha and Beta Capricorni now to its lower right.

-Have you noticed an extremely luminous star in the southwest after sunset? That's no star. It's Venus, and tonight it is at its brightest for all of 2013. Only the Moon itself outshines the 2nd planet from the sun.

Astronomers are mourning the loss of Comet ISON, which disintegrated when it flew past the sun on Thanksgiving Day (Nov. 28). Who needs it? There is another comet brightening in the morning sky--naked-eye Comet Lovejoy (C/2013 R1). Martin McKenna sends this report from Northern Ireland: "This morning, the comet was easily visible as a fuzzy star of 4th magnitude with a long straight tail between the constellations Bootes and Hercules." He took this picture using a Canon 450D digital camera.

"I could see 5 degrees of tail with my unaided eye," continues McKenna. "Using the camera the tail was at least 10o long!"

Telescopes and longer exposures reveal much more. A "disconnection event" disrupting the comet's tail on Dec. 5th was recorded. The disturbance could be caused by a gust of solar wind or perhaps an episode of vigorous outgassing in the comet's core.

Monitoring is encouraged. Comet Lovejoy is easy to find before dawn rising in the east before the sun.

Astro Picture of the Day:
December 6, 2013

Source:
For an Earth-orbiting gamma-ray telescope, Earth is actually the brightest source of gamma-rays, the most energetic form of light. Gamma-rays from Earth are produced when high energy particles, cosmic rays from space, crash into the atmosphere. While that interaction blocks harmful radiation from reaching the surface, those gamma-rays dominate in this remarkable Earth and sky view from the orbiting Fermi Gamma-ray Space Telescope's Large Area Telescope. The image was constructed using only observations made when the center of our Milky Way galaxy was near the zenith, directly above the Fermi satellite. The zenith is mapped to the center of the field. The Earth and points near the nadir, directly below the satellite, are mapped to the edges of the field resulting in an Earth and all-sky projection from Fermi's orbital perspective. The color scheme shows low intensities of gamma-rays as blue and high intensities as yellowish hues on a logarithmic scale. Our fair planet's brighter gamma-ray glow floods the edges of field, the high intensity yellow ring tracing Earth's limb. Gamma-ray sources in the sky along the relatively faint Milky Way stretch diagonally across the middle. Launched June 11, 2008 to explore the high-energy Universe, this week Fermi celebrated its 2,000th day in low Earth orbit.

[Bluearrowll]

Re: Terry's Astronomy Thread.

What's in the sky tonight?
December 7, 2013

-Earliest sunset of the year (near 40° north latitude). The longest night won't come until December 21st at the solstice, and the latest sunrise doesn't happen until January 4th. The reason? Local Apparent Solar Time is shifting with respect to Local Mean Time during this part of the year, an effect caused by the tilt of Earth's axis and the ellipticity of Earth's orbit. Be glad that we use standard time, so you don't have to keep adjusting your clocks to the inconstant Sun like in olden days. Standard time made things simpler for society but complicated things for skywatchers.

-The sun's southern hemisphere is peppered with sunspots, but none of them is strongly flaring. Solar activity remains low. NOAA forecasters estimate a 15% chance of M-class solar flares and a scant 1% chance of X-flares on Dec. 6th.

Astro Picture of the Day:
December 7, 2013

Source:
Brightest stellar beacons of the constellation Centaurus, Alpha and Beta Centauri are easy to spot from the southern hemisphere. For now, so is new naked eye Nova Centauri 2013. In this night skyscape recorded near Las Campanas Observatory in the Chilean southern Atacama desert on December 5, the new star joins the old in the expansive constellation, seen at early morning hours through a greenish airglow. Caught by nova hunter John Seach from Australia on December 2 as it approached near naked eye brightness, Nova Cen 2013 has been spectroscopically identified as a classical nova, an interacting binary star system composed of a dense, hot white dwarf and cool, giant companion. Material from the companion star builds up as it falls onto the white dwarf's surface triggering a thermonuclear event. The cataclysmic blast results in a drastic increase in brightness and an expanding shell of debris. The stars are not destroyed, though. Classical novae are thought to recur when the flow of material onto the white dwarf eventually resumes and produces another outburst.