Mark your calendar. On May 26th, the full Moon will pass through the shadow of Earth producing a total lunar eclipse. For 14 and a half minutes, the disk of the Moon will turn orange--the same color as the core of our planet's shadow.
The eclipse will be visible from Antarctica, Australia, parts of Asia and the Americas: World Map. In the USA, the best place to be is near the west coast, where the eclipse will unfold in its entirety before sunrise. The low-hanging Moon will look extra big and beautiful because of the Moon Illusion. On the east coast, the eclipse will not be visible at all: USA Map.
Auroras still have the capacity to surprise. On April 16th, Matthew Wheeler, an experienced aurora-watcher in Robson Valley, British Columbia, saw a green glow forming in the north--then he noticed something odd. "Horizontal lines caught my attention", he says. "There appeared to be ripples in the aurora." Six of them are labeled in this 1/2 second exposure:
A video captured by Wheeler shows their dynamics over a 20-minute period: watch it.
These are "dunes", a newly recognized form of aurora named after their resemblance to desert sand dunes. A team of researchers first explained them in a paper published just last year. Dunes are a "mesospheric bore"--a type of atmospheric gravity wave that springs up from Earth's surface and gets caught in a thermal waveguide ~100 km high. When solar wind particles rain down on the bore, they illuminate its rippling structure.
Sky watchers in the Arctic have been seeing Dunes for years without understanding what they were. A breakthrough came on Oct. 7, 2018, when multiple groups photographed dunes from widely separated locations in Finland. Triangulation revealed the dunes to be ~100 km high with a pure, monochromatic wavelength of about 45 km.
This is a new field of study with potential for discovery. Monitoring aurora dunes may reveal previously hidden waves and waveguides at the boundary between Earth and space.
Jay Nelz, Philippine News, Thu, 15 Apr 2021
The mysterious cloud formation spotted in Oriental Mindoro garnered various speculations from the online community.
The Facebook page "Youth for Mindoro" has shared the amazing photos of a strange cloud formation in Mansalay, Oriental Mindoro. The phenomenon happened last Wednesday afternoon (April 14, 2021).
According to the witnesses, the mysterious light has been formed above the clouds. The weird light looks like a crown roaring above the cloudy, which garnered various reactions from the social media users.
The unique cloud formation has been already spotted in different parts of the world such as Costa Rica and America. The optical phenomenon usually appears when a ray of sunshine hits the ice crystal inside the clouds. The process results to formation of various colors within the clouds, which is called rainbow-effect. The refraction is also known as "cloud iridescence".
Here is the full post.
Spring is the season for sprites, and Paul Smith just photographed a magnificent display over Kansas. "These were my first big sprites of the season," says Smith, who took this picture on April 6th:
"They were so bright, I saw a couple of them with my unaided eyes," he adds.Sprites are a weird form of lightning that leap up from powerful thunderstorms. The ones Smith saw are "jellyfish sprites", named for their resemblance to sea creatures. Their red tentacles stretch about 90 km high, almost touching the edge of space. Other forms exist, too.
At this time of year, severe storms set the stage for sprite formation. Mesoscale convective systems sweep across the Great Plains, cracking with intense electric fields that drive electrons up and into sprites. La Niña conditions in the Pacific Ocean may amplify this process.
Although the sprites were in Kansas, Smith saw them from Oklahoma. This weather satellite image shows the observing geometry.
"I was about 200 miles away from the thunderstorm," says Smith. Turns out, that's about the right distance. You have to be far away to see sprites over the top of the thunderclouds.
Although sprites have been reported by pilots and storm chasers for more than a century, many scientists were skeptical. Can you blame them? "Doctor, I just saw a giant red jellyfish in the sky!" A turning point came in 1989 when sprites were photographed by researchers at the University of Minnesota and cameras onboard the space shuttle. Now sprites are in the mainstream. See for yourself.
The first hours of northern Spring were eventful. First, a solar wind stream hit Earth's magnetic field. Next, a crack opened. Then, "an amazing display of auroras rocked our world," says Todd Salat, who watched the light show from Trapper Creek, Alaska:
"As we entered the equinox on March 20th, the auroras spiraled out control!" he says.
During the G2-class geomagnetic storm, auroras were sighted across Canada and Alaska, in multiple northern-tier US states, and 35,000 feet above the Southern Ocean. STEVE made an appearance, too.
What caused the outburst? It's simple: Auroras love equinoxes. Around the beginning of spring and fall, cracks open in Earth's magnetic field--a phenomenon called 'the Russell-McPherron effect'. Solar wind pours in to fuel geomagnetic storms. An unusually large crack opened on March 20th, supercharging the display.
The same phenomenon could multiply the effect of the CME expected on March 23rd, turning a glancing blow into a nice show.
Although STEVE is not an aurora, he has an aurora side-kick: the "picket fence." Evenly-spaced blobs of green light often appear alongside or underneath STEVE during geomagnetic storms. Alan Dyer photographed these specimens on March 13th:
"STEVE put on a great show, appearing first as the characteristic purple arc then developing green picket fence fingers rippling from east to west," says Dyer.
What are these green pickets? A team of researchers led by Toshi Nishimura of Boston University may have found the answer. Using data from NASA's THEMIS spacecraft, they pinpointed STEVE's power source. More than 22,000 km above Earth's surface, magnetic explosions called "substorms" hurl streams of hot plasma toward Earth. When the streams reach an altitude ~250 km above Earth's surface, they begin to emit a soft-purple light. This is STEVE.
The same explosions spray energetic electrons toward Earth. The electrons move even deeper into the atmosphere, all the way down to 100 km, where they ignite fingers of green auroras. This is the picket fence.
So when you see STEVE, look for his sidekick as well. Sometimes the picket fence appears first, so one can herald the other. Either way, it's a beautiful show.
Northern spring is less than a week away. That means hot ribbons of plasma are starting to flow in Earth's magnetosphere. Fred Hirschmann just saw one of them over Glacier View, Alaska:
"Just after midnight on March 12th I was feeding our outdoor woodstove when I recognized the long narrow band of STEVE overhead," says Hirschmann.
STEVE--short for "Strong Thermal Emission Velocity Enhancement"--was long thought to be a type of aurora borealis. But it's not. Auroras appear when particles rain down from space. STEVE, on the other hand, does not require "rain." Instead, satellite measurements show that it is a ribbon of hot (3000°C) gas speeding through the upper reaches of Earth's magnetic field faster than 10,000 mph. The ribbon's purple hue is still a mystery; some research suggests the color comes from heated nitrogen, but the jury's still out..
Studies show that STEVE appears most often in weeks around equinoxes--that is, now. If you live at high latitudes, be alert for purple ribbons in the sky.
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.
Did you see last week's full Moon? It was unique. Why? Because no two full Moons are exactly alike. To prove it, Paolo Bardelli of Sumirago, Italy, photographed the last 12 full Moons and stacked the pictures to highlight their differences:
"From each full Moon photo, I cut out a slice, then placed the slices side by side," explains Bardelli. "The Moons of Jan. 10th and June 5th are dark because they are taken from shots of the penumbral eclipses that occurred in those days."
None of the slices are the same. Some are wide, others narrow. Each one faces in a slightly different direction. These differences are a result of the Moon's motion around its tilted, elliptical orbit. Each full Moon occurs at a different point in that orbit, and so we see it from a slightly different distance and angle.
Scroll up and down past the slices; they seem to rock back and forth. The rocking motions are called libration; because of them we can see 59% of the Moon's surface rather than the 50% you might have learned in school. So pay attention to the next full Moon (Jan 28th). It's as unique as you are.
Earth's orbit around the sun isn't a perfect circle, it's an ellipse. One side is closer to the sun (147.5 million km) than the other (152.6 million km). This weekend (Jan. 2nd), we're at the closest point, known to astronomers as perihelion. When Earth is at perihelion, the sun looks a little bigger than usual, as shown in this composite image from Khosro Jafarizadeh of Karaj, Alborz, Iran:
Jafarizadeh took the two pictures from opposite ends of Earth's orbit: perihelion and aphelion. Sunlight falling on Earth at perihelion is 3.5% stronger than the year-long average. Northern snow doesn't melt, however, because seasons are shaped primarily by the tilt of Earth's spin axis, not the eccentricity of its orbit.
"You've heard of a green flash on the sun. But a green flash on Jupiter? "I've never come across one before," says atmospheric optics expert Les Cowley. Until now, that is. Spanish astrophotographer Juan Manuel Perez Rayego captured the rare phenomenon on Dec. 26th:
"I was taking one last photo of the Great Conjunction between Jupiter and Venus, just saying goodbye," says Rayego. "Suddenly, a green fragment of Jupiter split off and floated away from the planet. It was spectacular. I've analyzed Juan's image and conclude that it is very likely a mock mirage--the same type of mirage that can create green flashes on the sun," says Cowley.
Mock mirages are caused by atmospheric temperature inversions, in which layers of air are warmer than usual. An extra 1 or 2 degrees Celsius is all it takes. Inversion layers can be quite close to ground. Indeed, Jupiter was only 1/3rd of a degree above the horizon of Arroyo de San Serván, Spain, when Rayego recorded the flash.
The low altitude of Jupiter is why the planet looked like a rainbow-colored smear when the flash occurred. The low atmosphere acts like a prism, spreading the light of stars and planets into their R-G-B components. In this wider-angle animation, Saturn may be seen as well (lower right). It too looks like a miniature rainbow, albeit without the green flash.
A parhelic circle is an unforgettable sight. Thin and pale, it circles the zenith in a majestic arc, always keeping the same distance above the horizon. On Dec. 27th, Göran Strand of Handöl, Sweden, saw a parhelic circle but, strangely, the sun was nowhere around. This parhelic circle was passing through the Moon:
"It has been a long time since I saw a lunar halo, and I can't remember the last time I saw one with such a prominent parhelic circle," says Strand. "It was an amazing sight."
The parhelic circle is not the ring around the Moon; that's a 22-degree halo. Instead it is the almost-horizontal arc cutting through the Moon. The rest of the parhelic circle was too big to fit in the field of view of Strand's camera.
Parhelic circles are formed by sunlight reflecting from the vertical faces of ice crystals--millions of them floating in thin cirrus clouds spread almost evenly across the sky. In this case, bright moonlight + cirrus clouds performed the same trick.
Note: Because this circle is caused by moonlight rather than sunlight, it is most correctly called a "parselenic circle."
In Iceland, the New Year began with a very special sunrise. "Just before the sun appeared on Jan. 1st, a pink shaft of light sprung up from the eastern horizon," says Wioleta Gorecka, who sends this picture from the port of Hafnarfjordur: "What a beautiful way to greet 2021," she says.
This is a sun pillar, caused by plate-shaped ice crystals fluttering like leaves in distant cirrus clouds. The crystals intercept sunbeams, bending and reflecting them into a tall column of light. Look for pillars around sunrise and sunset; they are especially easy to find in cold places like Iceland where icy clouds bookend the short days of winter.
Something special is happening in the sunset sky. It's a Great Conjunction of Jupiter and Saturn. The two giant planets are converging for a close encounter the likes of which have not been seen since the Middle Ages. Shahrin Ahmad of Kuala Lumpur, Malaysia, photographed the pair on Dec. 7th:
"Jupiter and Saturn are about 1.5º apart this evening, " says Ahmad. "Even under a light polluted sky, both can easily be seen."
They're about to get much closer. On Dec. 21st, the two planets will lie just 0.1 degrees apart. That's so close, some people will perceive them as a single brilliant star. Viewed through binoculars or a small telescope, ringed Saturn will appear as close to Jupiter as some of Jupiter's moons:
Although Great Conjunctions between Jupiter and Saturn occur every 20 years, they're not all easy to see. Often the two planets are hidden in the glare of the sun. This year is special because the conjunction happens comfortably away from the sun. In fact, the last time the two worlds were so close together and so easy to see was the year 1226, astronomer Michael Brown told the Washington Post.
The show is underway. Jupiter and Saturn are already a tight pair in the evening sky, and they will grow rapidly and noticeably closer together every night for the next two weeks. Dates of special interest include Dec. 16th and 17th, when the crescent Moon joins the planets, and, of course, Dec. 21st when they are almost touching. Sky maps: Dec. 16, 17; Dec. 21.
Astronomers studying novel atmospheric plasma phenomenon 'STEVE' publish paper on 'pure green sky canonballs'
Cap Allon, Electroverse, Thu, 26 Nov 2020
“Picket fence” below STEVE: Taken by Harlan Thomas on April 10, 2018 in Alberta, Canada.
Just when you thought "STEVE" couldn't get any weirder, a new paper published in the journal AGU Advances reveals that the luminous purple ribbon is often accompanied by green cannonballs of light that streak through the atmosphere at 1000 mph.
[Below is an abridged version of Dr. Tony Phillip's excellent article-the full version of which is available at spaceweatherarchive.com, dated November 22, 2020.]
STEVE (Strong Thermal Velocity Enhancement) is a relatively recent discovery, first spotted and photographed by Canadian citizen scientists around 10 years ago. It looks like an aurora, but it is not. The purple glow is caused by hot (3000 °C) rivers of gas flowing through Earth's magnetosphere faster than 13,000 mph. This distinguishes it from auroras, which are ignited by energetic particles raining down from space.
"Citizen scientists have been photographing these green streaks for years," says Joshua Semeter of Boston University, lead author of the new paper. "Now we're beginning to understand what they are."
There is a dawning realization that STEVE is more than just a purple ribbon, as photographers routinely catch it flowing over a sequence of green vertical pillars known as the "picket fence". These aren't auroras either.
And now, Semeter's team has identified yet another curiosity: "Beneath the picket fence, photographers often catch little horizontal streaks of green light," explains Semeter: "This is what we studied in our paper."
Read more at the link above.
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