There's something strange about Sirius. The brightest star in the sky is pulsing with color. To the naked eye, Sirius looks pale blue, almost white. But if you photograph it with a camera, using very short exposure times, Sirius reveals its true colors. Lots of them. Photographer Arne Recke of Broager, Denmark, just did the experiment, and this is what he found:

"Here are 16 pictures of Sirius," says Recke. "The uppermost picture was taken with 1/2 sec. shutter speed (ISO 6400). The other 15 pictures were taken much faster with a 1/500 sec.shutter speed (also ISO 6400). The short exposures are incredibly colorful."
Astronomers call this phenomenon "scintillation." It is caused by thermal irregularities in Earth's atmosphere. Packets of relatively warm and cool air act like prisms, spreading starlight into rainbow colors. When these packets drift in front of Sirius--voilá.
The reason Recke's first exposure looks white is because 1/2 sec. is long enough to average many colors together. Multiple packets of air drift by during that time. The shorter snapshots, however, capture individual packets; they look like tiny supernova explosions.
All stars scintillate, but Sirius does so most flamboyantly because of its extreme brightness. See for yourself. Step outside this evening an hour or so after sunset and look east for Sirius near the feet of Orion. The lower it is, the more it scintillates. You may be able to see the colors--no camera required.
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Jupiter and Saturn will come closer to each other in the Earth's night sky than they have for almost a millennium between December 16 and 25 in an extremely rare astronomical extravaganza. The pair will be separated by one fifth the diameter of a full moon as viewed from the Earth, in an extraordinary astronomical proximity event which has not occurred for 800 years.

The planets will appear as a singular point of brilliant light or a “double planet” to anyone lucky enough to have clear skies at the time of their yuletide rendezvous

“Alignments between these two planets are rather rare, occurring once every 20 years or so, but this conjunction is exceptionally rare because of how close the planets will appear to one another,” says astronomer Patrick Hartigan from Rice University.

For context, their previous closest celestial encounter on record (as we see them anyway) was on March 4, 1226.  As always, the best viewing conditions will be near the equator but, with clear enough skies, it should be visible from anywhere on Earth about an hour after sunset each evening.  Stargazers should point their telescopes toward the western sky, especially during the closest approach on December 21, when the pair will appear as a “double planet.”

“For most telescope viewers, each planet and several of their largest moons will be visible in the same field of view that evening,” Hartigan adds.

The viewing window will be shorter for those in the northern hemisphere, however, so stargazers are encouraged to make preparations well in advance and head out early to avoid missing the mesmerizing meeting.

Their next astronomical alignment is expected in March 2080 and then again in 2400.
https://www.rt.com/news/507528-jupiter-saturn-alignment-double-planet/
Read also: https://www.iceagenow.info/jupiter-and-saturn-about-to-do-something-not-seen-since-the-year-1226/

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"Don't panic! Betelgeuse is not likely to undergo a supernova explosion anytime soon," says South Korean research astronomer Bum-Suk Yeom. "The red supergiant star Betelgeuse appears to have finally stopped its unprecedented dimming. It's been brightening over the last few days." Yoem assembled this light curve from data collected by American Association of Variable Star Observers (AAVSO):

According to the data, Betelegeuse reached its minimum brightness between Feb. 12th and 14th, and now it is slowly brightening again.
This development was actually predicted. Ed Guinan and Richard Wasatonic of Villanova University recently suggested that Betelgeuse might "bounce back" within a week of Feb. 21st. Their prediction was based on a Fourier analysis of Betelgeuse's light curve, which revealed a strong 430-day period. If the current dimming was just an unusually deep dip in Betelgeuse's natural 430-day variability, they reasoned, its brightness should start to increase again on Feb 21st +/- 7 days.
Their prediction seems to be coming true. However, it is too early to draw a firm conclusion because the turnaround--if that is indeed what is happening---is still in its early stages.
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One day, perhaps in our lifetimes, perhaps 100,000 years from now, the red giant Betelgeuse will dim a little--and then explode. The supernova will rival the full Moon in the night skies of Earth and cast shadows after dark. This month, Betelgeuse has dimmed a little. So far it has not exploded. Alan Dyer photographed the star rising as usual with the rest of Orion on Dec. 21st:

"This is Orion rising over my home in Alberta, Canada, on a partly cloudy and foggy night," says Dyer. "Yellow-red Betelgeuse is shining at upper left, reportedly dimmer than usual."
Betelgeuse caused a sensation among professional astronomers earlier this month when Edward Guinan of Villanova University and colleagues reported a significant "fainting" of the star. "[Betelgeuse] has been declining in brightness since October 2019, now reaching a modern all-time low of V = +1.12 mag on 07 December 2019 UT," they wrote. "Currently this is the faintest the star has been during our 25+ years of continuous monitoring."
Astronomers have long known that Betelgeuse is on the precipice of an energy crisis. It's about to run out of fuel in its core. When that happens, the star will collapse and rebound explosively, producing the first known supernova in the Milky Way since 1604. Experts in stellar evolution believe Betelgeuse could die at any time during the next 100,000 years--a blink of an eye on time scales of astronomy.
The current dimming did not herald that final blast. Betelgeuse is also a slow variable star, and this seems to be no more than an episode of slightly deeper-than-usual dimming.  Orion remains intact ... for now.
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Over the weekend, Comet 46P/Wirtanen made history. The green ball of gas wrapped around a nugget of dirty ice flew past Earth only 11.5 million km away--so close that it cracked the top 10 list of comet flybys during the Space Age. During the hours of closest approach, 46P/Wirtanen appeared in the constellation Taurus alongside the Pleiades star cluster:

Michael Jäger took the picture on Dec. 16th from Turmkogel, Austria. "To create the image, I combined 6-minute exposures through red, green and blue filters," says Jäger.

The colors in Jäger's image are remarkable--a striking contrast of green vs. blue.  Wirtanen's green comes from diatomic carbon (C2)--a gaseous substance common in comet atmospheres that glows green in the near-vacuum of space. The Pleiades, on the other hand, appear blue because the stars themselves are that color. Hot and massive, the Seven Sisters shine their blue light into surrounding clouds of gas and dust, which reflect the azure hue.

46P/Wirtanen is receding from Earth now, but it will still be nearby for days to come. The main challenge for observers is not distance, but rather moonlight. The glare of the waxing Moon will dilute the comet's brightness, making it a challenge to see with the unaided eye. Digital cameras and widefield telescopes will have no trouble, however, capturing the comet's exit. It is currently glowing like a big misty star of 4th magnitude near the horns of the Bull:

Well, bang go those theories. Astrophysicists have identified a neutron star that overturns not one but three well supported hypotheses.

The star, known as NGC 5907 ULX, is emitting far more x-rays than any other ever observed.  So huge is the output that it has been classified as an "ultraluminous x-ray source" (ULX). It is by no means the first ULX to be recorded in nearby galaxies, but all the others are confidently predicted to be generated by black holes - this is the first one that uses star-power.

So there goes the first theory.

But there are still more baffling elements to the discovery, made by a team led by Gianluca Israel from the National Institute of Astrophysics in Rome, Italy, and reported in Science.

For a start, until now it was thought that there was a physical constraint that prevented a neutron glowing as brightly as NGC 5907 ULX. It's called the Eddington limit, which describes the theoretical maximum set by the balance between the force of radiation acting outward and the gravitational force acting inward.

This star exceeds the Eddington limit by 1,000 times - which shouldn't be possible, but evidently is. So there goes theory number two.

The third theory that has taken a battering is one that is familiar to every primary school pupil: magnets, planets and stars have two poles. Ordinary stars do, of course, but NGC 5907 ULX is far from ordinary.

Israel and colleagues contend that the only way the star could achieve such an extremely high output is by having multiple magnetic poles.

"Such high luminosities are often displayed by many ULXs that have previously been classified as accreting black holes," they write.  "A multicomponent strong magnetic field is necessary to account for the properties of NGC 5907 ULX."

Shining bright red in the heart of the constellation Scorpius, 1st-magnitude star Antares is often mistaken for Mars. In Greek, "Antares" means "rival of Mars" or "anti-Mars," so-named because it is about the same brightness and color as the Red Planet. As September comes to a close, the rivals are converging. Jeff Dai sends this photo of Mars and Antares setting side-by-side behind Mount Balang in Sichuan, China:

"I was looking southwest in the evening sky on Sept. 20th when a conspicuous pair of ruddy objects grabbed my attention," says Dai. "Red planet Mars is moving in for a close encounter with its ancient rival, the red supergiant star Antares."

On Sept. 28th and 29th, the nights of closest approach, Mars and Antares will be only a few degrees apart, a conjunction tight enough to fit behind your outstretched palm. Sept. 29th is the best night to look because the Moon will join the display, lining up to form a near-vertical column of heavenly bodies just above the southwestern horizon. Sept. 27th is a good night, too, but for a different reason: A slender crescent Moon will pass very close to Saturn not far from Antares and Mars. Sky maps: Sept. 25, 26, 27, 28, 29.      www.spaceweather.com

The sun is hitting its stride. Earth's closest star shot off yet another powerful solar flare today (June 11) after producing a pair of major solar storms Tuesday.   The X1-class flare reached its peak at 5:06 a.m. EDT (0906 GMT) and came from Region 2087 near the southeastern limb of the sun's disk, the same region of the star that produced the two powerful solar flares yesterday. NASA captured an amazing video of the X1 solar flare using its space-based Solar Dynamics Observatory.

Today's solar tempest did cause a brief radio blackout on Earth, but officials with the U.S. Space Weather Prediction Center based in Boulder, Colorado, don't think that the flare has an associated coronal mass ejection - a burst of hot plasma sent out from the sun during some solar flares.   While officials with the SWPC didn't initially think that Tuesday's flares produced a coronal mass ejection - a burst of plasma associated with some solar flares - later analysis shows that the flares did produced two CMEs. The first solar flare produced a relatively small CME, with the second merging with it shortly after, according to astronomer Tony Phillips at spaceweather.com.  The CME is expected to give Earth a glancing blow, when it reaches our part of the solar system Friday (June 13). It's possible that the incoming CME could create polar geomagnetic storms, according to Phillips.

The sun is in the active phase of its 11-year solar cycle, called Solar Cycle 24. NASA officials now think the sun is in its maximum, which they have dubbed the "mini max". Although the sun's activity is on the upswing, this solar max is still quite weak by comparison to other solar maximums on record, NASA officials have said. Scientists expected that the solar maximum (the peak in the sun's activity for the cycle) would occur in 2013.

"It's back," Dean Pesnell, of NASA's Goddard Space Flight Center, said in a NASA statement Tuesday (June 10) on the sun's weather cycle. "Solar max has arrived."

Wednesday's solar flare is the eighth documented X-flare shot out from the sun in 2014. The most powerful flare of the year - a monster X4.9-class flare - occurred in February. X2 flares are two times as intense as X1 flares. If aimed toward Earth, X-flares can damage the planet's power grids and put satellites and astronauts in space in danger.

The sun also shoots out other, less powerful classes of solar flares. M-class flares can produce incredible auroras, and our nearest star also emits weaker C-class flares.

NASA has a fleet of sun-monitoring satellites in orbit today. The Solar Dynamics Observatory, the space agency's twin STEREO probes and the joint U.S.-European SOHO spacecraft all keep watch on the sun from space.

Shannon Hall;  Universe Today;  Tue, 06 May 2014 16:26 CDT

© NASA/Swift/Mary Pat Hrybyk-Keith and John Jones
This artist’s impression shows a gamma-ray burst with two intense beams of relativistic matter emitted by the black hole.

Roughly once a day the sky is lit up by a mysterious torrent of energy. These events - known as gamma-ray bursts - represent the most powerful explosions in the cosmos, sending out as much energy in a fraction of a second as our Sun will give off during its entire lifespan.  
Yet no one has ever witnessed a gamma-ray burst directly. Instead astronomers are left to study their fading light.

New research from an international team of astronomers has discovered a puzzling feature within one Gamma-ray burst, suggesting that these objects may behave differently than previously thought.

These powerful explosions are thought to be triggered when dying stars collapse into jet-spewing black holes. While this stage only lasts a few minutes, its afterglow - slowly fading emission that can be seen at all wavelengths (including visible light) - will last for a few days to weeks. It is from this afterglow that astronomers meticulously try to understand these enigmatic explosions.

The afterglow emission is formed when the jets collide with the material surrounding the dying star. They cause a shockwave, moving at high velocities, in which electrons are being accelerated to tremendous energies. However, this acceleration process is still poorly understood. The key is in detecting the afterglow's polarization - the fraction of light waves that move with a preferred plane of vibration.

"Different theories for electron acceleration and light emission within the afterglow all predict different levels of linear polarization, but theories all agreed that there should be no circular polarization in visible light," said lead author Klaas Wiersema in a press release.   "This is where we came in: we decided to test this by carefully measuring both the linear and circular polarization of one afterglow, of GRB 121024A, detected by the Swift satellite."

And to their surprise, the team detected circular polarization, meaning that the light waves are moving together in a uniform, spiral motion as they travel. The gamma-ray burst was 1000 times more polarized than expected. "It is a very nice example of observations ruling out most of the existing theoretical predictions," said Wiersema.   The detection shows that current theories need to be re-examined. Scientists expected any circular polarization to be washed out. The radiation of so many electrons travelings billions of light-years would erase any signal. But the new discovery suggests that there could be some sort of order in the way these electrons travel.

Of course the possibility remains that this particular afterglow was simply an oddball and not all afterglows behave like this. 
Nonetheless "extreme shocks like the ones in GRB afterglows are great natural laboratories to push our understanding of physics beyond the ranges that can be explored in laboratories," said Wiersema.  ( The paper has been published in Nature. )

Using NASA's Kepler Space Telescope, astronomers have discovered the first Earth-size planet orbiting in the "habitable zone" of another star. The planet, named "Kepler-186f" orbits an M dwarf, or red dwarf, a class of stars that makes up 70 percent of the stars in the Milky Way: full story.        http://spaceweather.com/

This is a good week to see the planet Mars. Today, April 8th, Mars is "at opposition"--that is, perfectly opposite the sun in the midnight sky. And then, on April 14th, Mars makes its closest approach to Earth since 2012.

Look for the Red Planet rising in the east at sunset, shining brighter than a 1st-magntitude star. Alan Dyer sends this picture of the Red Planet from Coonabarabran, NSW, Australia:

"The reddish tint of Mars contrasts nicely with blue-white Spica, the brightest star in Virgo," says Dyer. "If the arrangement of Mars and Spica looks unusual, it's because I took this from Australia. So the relative position of Mars and Spica looks upside down compared to a northern hemisphere view. The gum trees in the foreground are illuminated by the waxing Moon."

To learn more about the close encounter, watch the video "Opposition of Mars" from Science@NASA.

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