The Return of STEVE

Sept. 5, 2019: Sky watchers are still sorting out all the things they saw during last weekend’s Labor Day geomagnetic storm.  Upon further review, not every light in the sky was the aurora borealis. There was also STEVE:

“Look at the mauve-colored plume. That’s STEVE,” says Alan Dyer, who took the picture at the Saskatchewan Summer Star Party on Aug. 31st. “We saw STEVE two nights in a row from our area in western Canada.”

STEVE (Strong Thermal Emission Velocity Enhancement) looks like an aurora, but it is not. The phenomenon is caused by hot (3000°C) ribbons of gas flowing through Earth’s magnetosphere at speeds exceeding 6 km/s (13,000 mph). These ribbons appear during some geomagnetic storms, revealing themselves by their soft purple glow.

Earlier this year, researchers led by Toshi Nishimura of Boston University published an important paper about STEVE. Using data from NASA’s THEMIS spacecraft, they located STEVE’s power source: Magnetic explosions called ‘substorms‘ more than 22,000 km above Earth’s surface hurl streams of hot plasma toward Earth. When the material reaches an altitude ~250 km above Earth’s surface, it begins to emit a mauve light.

There’s more. THEMIS data showed that the same explosions can spray energetic electrons toward Earth. These electrons move even deeper into the atmosphere, all the way down to 100 km, where they ignite a form of green auroras called “the picket fence.” Indeed, many sky watchers saw the picket fence beneath STEVE over Labor Day weekend:

“STEVE and the green pickets were quite strong underneath the handle of the Big Dipper,” says Philip Granrud, who took the picture from Kalispell, Montana, on Sept. 1st. “It was beautiful!”

Nishimura’s study showed that STEVE and the green pickets are inextricably connected. “They are two different manifestations of a single magnetic explosion high above Earth,” explains Nishimura. “The picket fence is an aurora. STEVE is not. Nevertheless, they are linked.”

The colors of the display are only partially understood. Picket fences are green because of oxygen, which emits green photons when it is pummeled by energetic electrons. The purple color of STEVE … is still a mystery. “We are looking at this more closely in a follow-up study,” says Nishimura. “We suspect that nitrogen is involved, but we are not yet certain.”

Ready for more? Good news. The season for STEVE is now. Studies show that STEVE tends to occur more frequently during spring and fall than summer and winter. The onset of northern autumn, only weeks away, seems to lure the arc out of summer hiding. Stay tuned.  Aurora alerts: SMS Text

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The Labor Day Geomagnetic Storm of 2019

Sept. 3, 2019: It happened just as predicted. On August 31st, a stream of solar wind hit Earth’s magnetic field, sparking the strongest geomagnetic storm of 2019. Episodes of G2-class storming ignited bright auroras over both poles visible even in Arctic twilight. Dmitry Rak photographed the display from  the Barents Sea coast near Teriberka, Russia:

“The aurora borealis mixed with the colors of sunset and dawn as the storm lasted the whole night of Aug. 31st to Sept. 1st,” reports Rak. “The most delicious auroras floated over us and headed south, so we were able to capture only part of this celestial extravaganza. Nevertheless, we were very satisfied with what we saw.”

Thousands of miles away in Wyoming, the sky and the ground both exploded:

“I got several images of the auroras over the geysers in Yellowstone National Park,” says photographer Jean Clark. “What a great night!”

At the peak of the storm, which lasted throughout the Labor Day weekend, auroras spilled across the Canadian border into multiple US states including Wisconsin, Michigan, Montana, Wyoming, Idaho, Maine and even Midwestern airspace.

Did you miss the show? The same stream of solar wind will return on Sept. 27th when the sun has spun once on its axis, directing the gaseous firehose at Earth again. Mark your calendar! Aurora alerts: SMS Text

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A “Super Sprite” over China

August 30, 2019: You never know what you might see in the wake of a big storm. On Aug. 25th, Chinese astrophotographer Chao Shen of Shaoxing City went outside to photograph the Milky Way. A typhoon named “White Deer” had passed through the day before, and the storm clouds were parting. “I saw the stars–but that’s not all,” says Shen. “A Gigantic Jet leaped up right before my eyes!”


Gigantic Jets are lightning-like discharges that spring from the tops of thunderstorms, reaching all the way to the edge of space. They’re related to sprites, but larger and more powerful.

“Shen definitely caught a Gigantic Jet,” confirms Oscar van der Velde of the Lightning Research Group at the Universitat Politècnica de Catalunya. “It looks like it may have reached as high as 90 km above the ground.”

“Gigantic Jets are much more rare than sprites,” says van der Velde. “While sprites were discovered in 1989 and have since been photographed by the thousands, it was not until 2001-2002 that Gigantic Jets were first recorded from Puerto Rico and Taiwan.” Only dozens of Gigantic Jets have ever been photographed.

Shen says that “the Jet came from a storm about 100 km southwest of me. It was so huge, I was able to see it clearly despite the distance.”

Above: The arrow in this weather map points from Chao Shen’s camera toward the jet-producing storm.

Observers of sprites may be wondering if Shen really saw this jet. The answer is “yes.” Unlike sprites, which flicker so rapidly that they are difficult to see with the unaided eye. Gigantic Jets can lasts for hundreds of milliseconds, long enough for human eyes to register their purple glow.

Gigantic jets are part of a growing menagerie of strange forms that appear above intense thunderstorms, including sprites, elves, trolls, and blue jets. Some researchers believe that cosmic rays help trigger these “transient luminous events” by ionizing the air in and around thunderheads. If so, now is a good time to look for Gigantic Jets, because cosmic rays are nearing a Space Age high. Thank you, Solar Minimum!

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Why Are Sunsets Turning Purple?

Aug. 28, 2019: Every year, on average, about 60 volcanoes erupt somewhere on Earth, shooting ashy plumes of sulfurous gas thousands of feet into the air. Rarely do those plumes make it all the way up to the stratosphere. This summer, however, two volcanoes have done it. The Raikoke volcano in the Kirul Islands (June 22nd) and the Ulawun volcano in New Guinea (Aug. 3rd) both punched through to the stratosphere, sending material as high as 60,000 ft.

The action of these two volcanoes may explain why many sky watchers are starting to notice purple sunsets. Juli Fowler of Albuquerque, New Mexico, photographed this example on Aug. 24th:

“Spectacular sunsets are a regular thing here in the Land of Enchantment, but imagine my surprise when I saw these violet beams caused by volcanic aerosols in the stratosphere,” says Fowler. “Wow!”

Why purple? Fine volcanic aerosols in the stratosphere scatter blue light which, when mixed with ordinary sunset red, produces a violet hue. The purple color is often preceded by a yellow arch hugging the horizon. As the sun sets, violet beams emerge from the yellow, overlapping to fill the western sky with a soft purple glow. High-quality pictures of the phenomenon often show horizontal bands cross-crossing the yellow arch. These bands are the volcanic gas.

Ray Majoran of London, Ontario, Canada, captured this dramatic image using a drone:

“Sunsets lately have a beautiful purple/pink glow to them, so I have been launching my Mavic 2 Pro drone to photograph them,” says Majoran. “This picture was taken just a few days after the Ulawun volcano eruption in New Guinea.”

Sky watchers shouldn’t expect to see purple every night. The volcanic gas appears to be patchily distributed, bringing strange sunsets on some nights, not all. Clear air, lack of clouds, and country settings improves their visibility. If you photograph one, send us your pictures!

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A New Source of Space Radiation

August 9, 2019: Astronauts are surrounded by danger: hard vacuum, solar flares, cosmic rays. Researchers from UCLA have just added a new item to the list. Earth itself.

“A natural particle accelerator only 40,000 miles above Earth’s surface is producing ‘killer electrons’ moving close to the speed of light,” says Terry Liu, a newly-minted PhD who studied the phenomenon as part of his thesis with UCLA Prof. Vassilis Angelopoulos.

This means that astronauts leaving Earth for Mars could be peppered by radiation coming at them from behind–from the direction of their own home planet.


NASA’s THEMIS spacecraft ran across the particles in 2008 not far from the place where the solar wind slams into Earth’s magnetic field. Researchers have long known that shock waves at that location could accelerate particles to high energies–but not this high. The particles coming out of the Earth-solar wind interface have energies up to 100,000 electron volts, ten times greater than previously expected.

How is this possible? Liu found the answer using THEMIS data and computer simulations of the sun-Earth interface. When the solar wind meets Earth, it forms a shock wave around Earth’s magnetic field, shaped like the bow waves that form ahead of a boat moving through water. Within this “bow shock” immense stores of energy can be abruptly released akin to the sonic boom of an airplane.

Liu found that some electrons are shocked not just once, but twice or more, undergoing mirror-like reflections within the bow shock that build energy to unexpected levels. Most of the boosted particles shoot back into space away from Earth.


Above: Terry Liu created this diagram showing the location of the natural particle accelerator and how it spews radiation into space.

“Similar particles have been detected near Saturn, suggesting that the process is at work there as well,” says Liu.

“Indeed,” adds Angelopoulos, “this type of particle acceleration could be happening throughout the cosmos–from supernovas to solar storms–wherever a supersonic wind hits a barrier such as Earth’s magnetosphere.”

Meanwhile, back home, Earth-orbiting satellites and departing astronauts have a new source of radiation to contend with. It’s right over their shoulder.

Read the original research at Science Advances.

Raikoke Sunsets

Aug. 4, 2019: Over the weekend in DeSoto, Kansas, something strange happened to the sunset: It turned purple. “On Saturday night, I photographed a large dome of pinkish-purple light,” reports Doug Zubenel. “Strong crepuscular rays were also visible.”

Photo credit: Doug Zubenel of DeSoto, Kansas. August 3, 2019.

Purple sunsets are a sign of volcanic activity. Fine volcanic aerosols in the stratosphere scatter blue light which, when mixed with ordinary sunset red, produces a violet hue.

But which volcano? The answer is probably Raikoke, a volcano in the Kuril islands which erupted with such force on June 22, 2019, that it was seen from the International Space Station. NASA satellites confirm that aerosols from Raikoke reached the stratosphere and they have been circulating around the Northern Hemisphere ever since.

A similar eruption occurred 11 years ago, in Aug. 2008, when Alaska’s Kasatochi volcano spewed sulfurous gases into the stratosphere. For months sky watchers witnessed strange sunsets whenever a plume of Kasatochi’s emissions drifted overhead. The same thing, apparently, is happening now thanks to Raikoke.

Photo credit: Heiko Ulbricht in the Zittau Mountains of southeastern Germany. July 26, 2019.

Volcanic sunsets have also been seen in Halifax, Nova Scotia; in the Zittau Mountains of Germany; in Joshua Tree, California; in Orange, California.

Purple isn’t the only thing to look for, says atmospheric optics expert Les Cowley. In addition, he advises, sky watchers should “be alert for a very bright yellow twilight arch, fine cloud structure in the arch seen through binoculars, and long diffuse rays and shadows.”

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Cosmic Ray Update: New Results from the Moon

July 16, 2019: Note to astronauts: 2019 is not a good year to fly into deep space. In fact, it’s shaping up to be one of the worst of the Space Age.

The reason is, the solar cycle. One of the deepest Solar Minima of the past century is underway now. As the sun’s magnetic field weakens, cosmic rays from deep space are flooding into the solar system, posing potential health risks to astronauts.

NASA is monitoring the situation with a radiation sensor in lunar orbit. The Cosmic Ray Telescope for the Effects of Radiation (CRaTER) has been circling the Moon on NASA’s Lunar Reconnaissance Orbiter spacecraft since 2009. Researchers have just published a paper in the journal Space Weather describing CRaTER’s latest findings.


Above: An artist’s concept of Lunar Reconnaissance Orbiter.

“The overall decrease in solar activity in this period has led to an increased flux of energetic particles, to levels that are approaching those observed during the previous solar minimum in 2009/2010, which was the deepest minimum of the Space Age,” write the authors, led by Cary Zeitlin of NASA’s Johnson Space Flight Center. “The data have implications for human exploration of deep space.”

This always happens during Solar Minimum. As solar activity goes down, cosmic rays go up. The last two Solar Minima have been unusually deep, leading to high cosmic ray fluxes in 2008-2010 and again in 2018-2019. These are the worst years since humans first left Earth in the 1960s.

“It’s a bit counterintuitive,” says one of the authors, Nathan Schwadron, a space physicist at the University of New Hampshire. “Solar Minimum may actually be more dangerous than Solar Maximum.”

In their paper, Zeitlin, Schwadron and co-authors describe an interesting experiment by NASA that highlights the relative peril of solar flares vs. cosmic rays. In 2011, NASA launched the Curiosity rover to Mars. Inside its spacecraft, the rover was protected by about as much shielding (20 gm/cm^2) as a human astronaut would have. A radiation sensor tucked inside kept track of Curiosity’s exposure.

The results were surprising. During the 9-month journey to Mars, radiation from solar flares (including the strongest flare of the previous solar cycle) accounted for only about 5% of Curiosity’s total dose. The remaining 95% came from cosmic rays.

Why the imbalance? “Solar flares of the size we’ve seen during the Space Age can be largely mitigated by achievable depths of spacecraft shielding(1),” explains Zeitlin. “We can’t stop the highest energy cosmic rays, however. They penetrate the walls of any spacecraft.”


Above: Since 2015, the flux of cosmic rays at the Moon has nearly doubled. Another plot shows the complete CRaTER record starting in 2010.

Solar flares are still a concern. If an astronaut were caught outside on EVA during an intense, unexpected flare, acute effects could include vomiting, fatigue, and low blood counts. A quick return to Earth might be required for medical care. Cosmic rays are more insidious, acting slowly, with maladies such as cancer or heart disease showing up years after the exposure.

As 2019 unfolds, Solar Minimum appears to still be deepening. Cosmic rays haven’t quite broken the Space Age record set in 2009-2010, but they’re getting close, only percentage points from the highest values CRaTER has ever recorded.

“No one can predict what will happen next,” says Schwadron. “However, the situation speaks for itself: We are experiencing a period of unusually weak solar cycles. We have to be prepared for strong cosmic rays.”


(1) According to Zeitlin, “achievable” shielding depths will be at least 20 to 30 gm/cm^2. “Vehicles carrying humans into deep space will likely have storm shelters that will provide this much shielding or more, and that would indeed be sufficient – even for an event like the great solar flare of August 1972 during the Apollo program – to keep the accumulated dose below the 30-day limit.”


“Update on Galactic Cosmic Ray Integral Flux Measurements in Lunar Orbit With CRaTER”, by C. Zeitlin, N. A. Schwadron, H. E. Spence, A. P. Jordan, M. D. Looper, J. Wilson, J. E. Mazur, L. W. Townsend.

A Sunspot from the Next Solar Cycle

July 8, 2019: Solar Cycle 25 is coming to life. For the second time this month, a sunspot from the next solar cycle has emerged in the sun’s southern hemisphere. Numbered “AR2744”, it is inset in this magnetic map of the sun’s surface from NASA’s Solar Dynamics Observatory:

How do we know this sunspot belongs to Solar Cycle 25? Its magnetic polarity tells us so. Southern sunspots from old Solar Cycle 24 have a -/+ polarity. This sunspot is the opposite: +/-. According to Hale’s Law, sunspots switch polarities from one solar cycle to the next. AR2744 is therefore a member of Solar Cycle 25.

Solar cycles always mix together at their boundaries. Right now we are experiencing the tail end of decaying Solar Cycle 24. AR2744 shows that we are simultaneously experiencing the first stirrings of Solar Cycle 25. The transition between Solar Cycle 24 and Solar Cycle 25 is underway.

Shortlived “ephemeral sunspots” belonging to Solar Cycle 25 have already been reported on Dec. 20, 2016; April 8, 2018; Nov. 17, 2018; May 28, 2019 and July 1, 2019. Today’s sunspot is more important than those earlier examples because it has lasted long enough to receive a numerical designation: AR2744. Record-keepers will likely mark this as the first official sunspot of Solar Cycle 25.

This development does not mean Solar Minimum is finished. On the contrary, low solar activity will probably continue for at least another year as Solar Cycle 24 decays and Solar Cycle 25 slowly sputters to life. AR2744 is an important sign, however, that the next solar cycle is approaching.

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Sunset Solar Eclipse

July 1, 2019: Residents of Chile and Argentina are about to witness a rare total eclipse of the sun. On July 2, 2019, the new Moon will pass across the solar disk, creating a black hole in the sky just before sunset in the two South American countries. This animated map, created by space artist Larry Koehn, includes a local timetable of events:


The path of totality cuts across ESO’s La Silla Observatory in Chile and barely misses the center of Buenos Aires in Argentina. The Moon’s elongated sunset shadow will swallow observers for 1 to 2 minutes depending on their exact location.

Outside the path of totality, the eclipse is partial with significant coverage in large cities such as Santiago, Chile (93%); Montevideo, Uruguay (94%); La Paz, Bolivia (63%); and Lima, Peru (54%). During the partial phase of the eclipse, the sun looks like a crescent, and it casts crescent-shaped shadows on the ground. South Americans should look for them underneath the canopies of leafy trees. Using safe eclipse glasses, it is possible to view the crescent sun directly.

The sun and Moon align for an eclipse once or twice every year. Aligning directly over a major observatory, however, is very rare. This video shows what the eclipse will look like over La Silla:

La Silla is home to some of the world’s biggest telescopes and many skilled observers. Observatory staff will host more than a thousand members of the public in a viewing party among the telescope domes. A live high-definition webcast of the eclipse will be available on ESO’s website and on ESO’s Youtube Channel. The action begins on Tuesday, July 2nd. Stay tuned!

More live webcasts: from Chile; from Argentina; from La Silla.

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Nuke Sensors Detect Asteroid Explosion

June 25, 2019: On June 22nd at 21:25 UT, a small asteroid entered Earth’s atmosphere and exploded in broad daylight south of Puerto Rico. Airwaves recorded by the Comprehensive Nuclear Test Ban Treaty Organization’s infrasound station in Bermuda pegged the blast energy between 3 and 5 kilotons of TNT–a fraction of a WW II atomic bomb. The explosion was clearly visible in images from NOAA’s GOES-16 weather satellite:


This movie combines data from GOES-16’s Global Lightning Mapper and water vapor infrared spectrometer

Meteor expert Peter Brown of the University of Western Ontario says the infrasound signal is consistent with a “small multi-meter sized near-Earth asteroid.” According to data compiled by NASA’s Center for Near Earth Object Studies, asteroids of this size and energy hit Earth’s atmosphere about once a year. That means it’s rare–but not exceptionally so.

The asteroid fragmented as it ripped through the atmosphere. This infrared image from the GOES-16 satellite shows the space rock splitting into at least 3 pieces:


Many more fragments undoubtedly sprayed from the explosion, but the resulting meteorites are now at the bottom of the Caribbean or (in the case of dust-sized debris) floating on the sea surface. Samples would be very difficult to recover.

Earth is currently approaching the Taurid Swarm–a stream of rocky debris associated with the Tunguska Impact of 1908. Astronomers are eager for the close encounter, which begins in late June, so they can peer inside the swarm in search of dangerous asteroids. This fireball, however, is not a Taurid.

“Based on a preliminary orbit for the fireball, it does not appear to be part of the Taurid swarm,” says Paul Weigert of the University of Western Ontario. “Its orbit is typical of near-Earth asteroids which have escaped from the asteroid belt.”

UPDATE: This asteroid may have been discovered shortly before it struck by an Atlas Project Survey telescope: more.

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