Major Solar Flare and CME

Nov. 30, 2020: Yesterday (Nov. 29th at 1311UT), Earth-orbiting satellites detected the biggest solar flare in more than 3 years. NASA’s Solar Dynamics Observatory recorded this extreme-ultraviolet movie of the M4.4 category blast:

X-rays and UV radiation from the flare ionized the top of Earth’s atmosphere, producing a shortwave radio blackout over the South Atlantic: map. Ham radio operators and mariners may have noticed strange propagation effects at frequencies below 20 MHz, with some transmissions below 10 MHz completely extinquished.

Remarkably, this flare was even bigger than it seems. The blast site is located just behind the sun’s southeastern limb. As a result, the explosion was partially eclipsed by the body of the sun. It might have been an X-class event.

The flare also hurled a significant coronal mass ejection (CME) into space, shown here in a coronagraph movie from the Solar and Heliospheric Observatory (SOHO):

Update: At first it appeared that the CME would completely miss Earth. However, NOAA analysts believe that the outskirts of the cloud might deliver a glancing blow to Earth’s magnetic field on Dec. 1-2. If so, the impact could spark a minor G1-class geomagnetic storm with auroras over northern countries such as Canada, Iceland, Norway and Sweden.

It would be a different story if the main body of the CME hit. Then we would be anticipating a strong geomagnetic storm. Maybe next time!

“Next time” could be just days away. The hidden sunspot that produced this major event will rotate onto the Earthside of the sun during the next 24 hours or so. Then its ability to spark geomagnetic storms will be greatly increased. Instant solar flare alerts: SMS Text.

Little Green Cannonballs of Light

Nov. 22, 2020: 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 we call “STEVE” is often accompanied by green cannonballs of light that streak through the atmosphere at 1000 mph.

“Citizen scientists have been photographing these green streaks for years,” says Joshua Semeter of Boston University, lead author of the study. “Now we’re beginning to understand what they are.”

STEVE is a recent discovery. 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. Canadian aurora watchers first called attention to the phenomenon about 10 years ago, whimsically naming it STEVE; researchers have been studying it ever since.

There’s a dawning realization that STEVE is more than just a purple ribbon. Photographers often catch it flowing over a sequence of vertical pillars known as the “picket fence.” They’re not auroras either. And, now, Semeter’s team has identified yet another curiosity in their paper, entitled “The Mysterious Green Streaks Below STEVE.”

“Beneath the picket fence, photographers often catch little horizontal streaks of green light,” explains Semeter. “This is what we studied in our paper.”

Semeter’s team gathered pictures of the streaks taken by citizen scientists in Canada, the United States and New Zealand. In some cases, the same streaks were photographed by widely-separated photographers, allowing a triangulation of their position. Analyzing dozens of high-quality images, the researchers came to these conclusions:

1. The streaks are not streaks. They are actually point-like balls of gas moving horizontally through the sky. In photos, the ‘green cannonballs’ are smeared into streaks by the exposure time of the cameras.

2. The cannonballs are typically 350 meters wide, and located about 105 km above Earth’s surface.

3. The color of the cannonballs is pure green–much moreso than ordinary green auroras, reinforcing the conclusion that they are different phenomena.

Above: The pure green of STEVE’s cannonballs (upper left) is compared to the blue-green and other mixed colors of auroras. Credit: Joshua Semeter, Boston University

So, what are the cannonballs? Semeter believes they are a sign of turbulence. “During strong geomagnetic storms, the plasma river that gives rise to STEVE flows at extreme supersonic velocities. Turbulent eddies and whirls dump some of their energy into the green cannonballs.”

This idea may explain their pure color. Auroras tend to be a mixture of hues caused by energetic particles raining down through the upper atmosphere. The ‘rain’ strikes atoms, ions, and molecules of oxygen and nitrogen over a wide range of altitudes. A hodge-podge of color naturally results from this chaotic process. STEVE’s cannonballs, on the other hand, are monochromatic. Local turbulence excites only oxygen atoms in a relatively small volume of space, producing a pure green at 557.7 nm; there is no mixture.

“It all seems to fit together, but we still have a lot to learn,” says Semeter. “Advancing this physics will benefit greatly from the continued involvement of citizen scientists.”

If you’re an aurora photographer looking to contribute, be sure to read Semeter et al’s original research at

Bright Comet Erasmus

Nov. 21, 2020: Every 2000 years, Comet Erasmus (C/2020 S3) visits the inner Solar System. News Flash: It’s back. Discovered on Sept. 17, 2020, by South African astronomer Nicolas Erasmus, the dirty snowball is plunging toward the sun for a close encounter inside the orbit of Mercury on Dec. 12th. This is what it looks like:

Gerald Rhemann took the picture Friday morning, Nov. 20th, using a 12-inch telescope in Farm Tivoli, Namibia. “The tail is magnificent,” he says. “In fact, I couldn’t fit it in a single field of view. This two-panel composite shows the first 3 degrees–and it keeps going well past the edge of the photo.”

Comet Erasmus is brightening as it approaches the sun. Right now it is 7th magnitude–an easy target for backyard telescopes. Forecasters believe it will more than triple in brightness to 5th magnitude by the time it dips inside the orbit of Mercury next month. Only the glare of the nearby sun will prevent it from being visible to the naked eye.

Where should you look? If you can find Venus, you can find the comet. Look low and southeast before sunrise. Comet Erasmus is in the constellation Hydra just to the right of Venus in neighboring Virgo. The bright star Spica is nearby, too, providing another useful reference point. Sky maps: Nov. 22, 23, 24, 25, 26.

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Suddenly, A Dark Streak Appears on Mars

Oct. 25, 2020: On Friday night, Oct. 22nd, longtime Mars photographer Maximilian Teodorescu of Magurele, Romania, looked at the Red Planet and noticed something he hadn’t seen before. “There is a dark streak in the Tharsis volcanic plateau,” he says. The mystery smudge is circled in these two images separated by about 40 minutes:

“The feature was not visible just a few nights ago when I photographed the same region,” says Teodorescu, who offers an Oct. 19th image for comparison. “Now, I have seen it two nights in a row (Oct. 22nd and 23rd), and other observers have seen it, too.”

What is it? Teodorescu’s first thought was “it must be some kind of cloud or streamer of dust.” Indeed, it is located in the same general area where a long icy cloud sometimes forms when wind whips around the summit of Arsia Mons, an extinct volcano.

To investigate further, Teodorescu projected the streak down onto a Mars Orbiter image of the region:

“The streak is about 600 km long,” he says. “It is close to Arsia Mons, but not a perfect match. Perhaps it is a shadow of the volcano’s ice cloud projected down onto lower Tharsis clouds.”

Mars photographers everywhere are encouraged to keep an eye out for this dark feature whenever the Tharsis volcanoes are facing Earth. Report your observations here, and we will share them.

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Rare Red Auroras

Oct. 13, 2020: Arctic photographer Rayann Elzein sees auroras all the time over Utsjoki, Finland. But the auroras he saw last night were different. “They were red,” he says. “Almost only red.”

“Rarely have I seen anything like this before,” says Elzein. “I double-checked the white balance on my camera to make sure nothing was wrong. But it was the same color temperature as on all my other northern lights pictures.”

“Later, we were treated to the usual swirls of green and even some pink nitrogen fringe,” he says. “When the green swirls calmed down, the red returned.”

Auroras are normally green–the verdant glow of oxygen atoms about 150 km above Earth’s surface. Rare red auroras are also caused by oxygen atoms, but at higher altitudes between 150 km and 500 km. At those heights, the temperature and density of the atmosphere favors atomic transitions that emit red photons. Indeed, Elzein’s photos show red stacked on top of green just as theory predicts.

For some reason, unknown to us, the solar wind on Oct. 12th excited oxygen at higher altitudes than usual, giving rare red auroras their chance to shine. Aurora alerts: SMS Text.

Aurora Cometalis: The Northern Lights of Comet 67P

Sept. 22, 2020: Imagine putting your thumb on a garden hose and sending a jet of water into the sky. At the apex of the stream, auroras form. It turns out, some comets can actually perform this trick.

In a paper published this week in Nature Astronomy, researchers described how comet 67P/Churyumov-Gerasimenko turns vaporous jets of water into auroras.

The European Space Agency’s Rosetta spacecraft observed the weird lights while it was orbiting Comet 67P in 2014-2016. At first researchers misunderstood what the glow was. It couldn’t be an aurora, could it? For one thing, the comet doesn’t even have a magnetic field–a key ingredient of geomagnetic storms. Also, the lights of Comet 67P are invisible to the human eye. They shine at far ultraviolet wavelengths, unlike the familiar red and green curtains that dance around Earth’s poles.

“Nevertheless, they are auroras,” says Marina Galand of Imperial College London, UK, lead author of the new study.

It took years for Galand and colleagues to figure out what was going on. Solving the mystery required data from five of Rosetta’s sensors plus a physics model to calculate how the solar wind interacts with the comet’s atmosphere.

They found that electric fields naturally occurring in the comet’s atmosphere can grab electrons from the solar wind and hurl them inward. Those electrons rush headlong into water molecules spewing out of the comet’s core. Debris from the collision–excited atoms of H and O–produce an ultraviolet glow: Aurora Cometalis.

Comet auroras respond to space weather much like Earth auroras do. Gusts of solar wind can rev them up, and a good coronal mass ejection (CME) can cause an outright auroral storm. Indeed, a CME that hit Comet 67P on Oct. 22, 2014, caused “a sharp intensification” of the UV brightness.

Galand says that “other comets should have these kind of auroras, too.” The basic physics is universal. 67P/Churyumov-Gerasimenko’s auroras are special only in the sense that the Rosetta spacecraft was there to observe them.

Thought experiment: Suppose you could see UV light. What would the auroras of Comet 67P look like from ground level? “They would be diffuse, but not uniform,” speculates Galand. “Some parts of the sky would be brighter than others–especially if a jet of water crossed your field of view!”

And here’s the strangest part of all: The auroras would descend all the way down to the comet’s surface. “So you would be surrounded by the light,” she says.

Yet another reason to visit a comet….

Solar Cycle 25 Has Begun

Sept. 15, 2020: Solar Cycle 25 is officially underway. NASA and NOAA made the announcement during a media teleconference earlier today. According to an international panel of experts, the sunspot number hit rock bottom in Dec. 2019, bringing an end to old Solar Cycle 24. Since then, sunspot counts have been slowly increasing, heralding new Solar Cycle 25.

“How quickly solar activity rises is an indicator on how strong the next solar cycle will be,” says Doug Biesecker of NOAA’s Space Weather Prediction Center, co-chair of the Solar Cycle 25 Prediction Panel. “Although we’ve seen a steady increase in sunspot activity this year, it is slow.”

The panel believes that new Solar Cycle 25 will be a weak one, peaking in 2025 at levels similar to old Solar Cycle 24. If their prediction is correct, Solar Cycle 25 (like Solar Cycle 24 before it) will be one of the weakest since record-keeping began in 1755.

“While we are not predicting a particularly active Solar Cycle 25, violent eruptions from the sun can occur at any time,” warns Biesecker. Indeed, even Solar Minimum can produce a superstorm, so Solar Cycle 25 should not be taken lightly despite the panel’s low expectations. Radio blackouts, power outages and severe geomagnetic storms are possible in the years ahead.

Above: Solar Cycle 25 auroras photographed on Sept. 14, 2020, by Jani Ylinampa in Finland.

For now, solar activity should remain generally low. Sunspot counts still have a long way to go before they reach levels typical of Solar Maximum. For the rest of 2020, periods of quiet will be occasionally interrupted by minor solar storms, with only a slight chance of big events.

On the bright side, the first Northern Lights of Solar Cycle 25 are dancing around the Arctic Circle right now, and the coming season for aurora watching promises to be the best in years. Stay tuned! Aurora alerts: SMS Text.

A Warning from History: The Carrington Event Was Not Unique

Sept. 1, 2020: On Sept. 1st, 1859, the most ferocious solar storm in recorded history engulfed our planet. It was “the Carrington Event,” named after British scientist Richard Carrington, who witnessed the flare that started it. The storm rocked Earth’s magnetic field, sparked auroras over Cuba, the Bahamas and Hawaii, set fire to telegraph stations, and wrote itself into history books as the Biggest. Solar. Storm. Ever.

But, sometimes, what you read in history books is wrong.

“The Carrington Event was not unique,” says Hisashi Hayakawa of Japan’s Nagoya University, whose recent study of solar storms has uncovered other events of comparable intensity. “While the Carrington Event has long been considered a once‐in‐a‐century catastrophe, historical observations warn us that this may be something that occurs much more frequently.”


Drawings of the Carrington sunspot by Richard Carrington on Sept. 1, 1859, and (inset) Heinrich Schwabe on Aug. 27, 1859. [Ref]

To generations of space weather forecasters who learned in school that the Carrington Event was one of a kind, these are unsettling thoughts. Modern technology is far more vulnerable to solar storms than 19th-century telegraphs. Think about GPS, the internet, and transcontinental power grids that can carry geomagnetic storm surges from coast to coast in a matter of minutes. A modern-day Carrington Event could cause widespread power outages along with disruptions to navigation, air travel, banking, and all forms of digital communication.

Many previous studies of solar superstorms leaned heavily on Western Hemisphere accounts, omitting data from the Eastern Hemisphere. This skewed perceptions of the Carrington Event, highlighting its importance while causing other superstorms to be overlooked.

A good example is the great storm of mid-September 1770, when extremely bright red auroras blanketed Japan and parts of China. Captain Cook himself saw the display from near Timor Island, south of Indonesia. Hayakawa and colleagues recently found drawings of the instigating sunspot, and it is twice the size of the Carrington sunspot group. Paintings, dairy entries, and other newfound records, especially from China, depict some of the lowest-latitude auroras ever, spread over a period of 9 days.


An eyewitness sketch of red auroras over Japan in mid-September 1770. [Ref]

“We conclude that the 1770 magnetic storm was comparable to the Carrington Event, at least in terms of auroral visibility,” wrote Hayakawa and colleagues in a 2017 Astrophysical Journal Letter. Moreover, “the duration of the storm activity was much longer than usual.”

Hayakawa’s team has delved into the history of other storms as well, examining Japanese diaries, Chinese and Korean government records, archives of the Russian Central Observatory, and log-books from ships at sea–all helping to form a more complete picture of events.

They found that superstorms in February 1872 and May 1921 were also comparable to the Carrington Event, with similar magnetic amplitudes and widespread auroras. Two more storms are nipping at Carrington’s heels: The Quebec Blackout of March 13, 1989, and an unnamed storm on Sept. 25, 1909, were only a factor of ~2 less intense. (Check Table 1 of Hayakawa et al‘s 2019 paper for details.)


Oriental reports of a giant naked-eye sunspot group (left) and auroras (right) in Feb. 1872. [Ref]

Contextualizing the Carrington Event has become a busy niche in space weather research. One team led by Jeff Love of the USGS recently confirmed the near equality of Carrington to the May 1921 superstorm. And Hayakawa’s team has just  unearthed new records of extreme auroras in South America.

Are we overdue for another Carrington Event? Maybe. In fact, we might have just missed one.

In July 2012, NASA and European spacecraft watched an extreme solar storm erupt from the sun and narrowly miss Earth. “If it had hit, we would still be picking up the pieces,” announced Daniel Baker of the University of Colorado at a NOAA Space Weather Workshop 2 years later. “It might have been stronger than the Carrington Event itself.”

History books, let the re-write begin.

Spiral Lights on Mars

August 25, 2020: NASA’s MAVEN spacecraft has discovered something unexpected on Mars–and researchers are struggling to explain it.

“There is a vast spiral of ultraviolet light over Mars’ South Pole,” says Nick Schneider of the University of Colorado’s Laboratory for Atmospheric and Space Physics. “We understand the origin of the light, but its shape is a mystery.”


Shown in false-color (green), a spiral of UV light is swirling around the Martian South Pole.

The light is “nightglow.” We have it here on Earth, too, where it’s called “airglow.” During the day, ultraviolet radiation from the sun breaks apart compounds in the upper atmosphere. At night, the atoms reassemble, glowing as they put themselves back together again. On Earth, airglow looks like the aurora borealis; people can actually see it. On Mars, the emission is ultraviolet, invisible to the human eye.

MAVEN has been monitoring Martian nightglow for years, yet the spiral pattern was only recently recognized. Schneider recalls the ‘Eureka moment’: “We were preparing a demo on our lab’s internal projection sphere (like Science on a Sphere), which turned out to be the first time we had plotted the UV glow in polar coordinates. The spiral ‘popped’ and we were all quite giddy.”


The chemistry of Martian nightglow. Nitric oxide (NO) also produces airglow on Earth.

The spiral is just the tip of the iceberg; the whole planet is surrounded by pulsating patterns of nightglow. High above the North Pole of Mars there is a luminous blob that pulses exactly twice a day. And around the equator there are three more blobs, evenly spaced, pulsing three times a day. Only the South Pole has a spiral, and it pulses once a day.

“It’s pretty complicated,” says Schneider.

To make sense of it all, Schneider and colleagues “spun up” a general circulation model (GCM) of the Martian atmosphere. (This part of the work was led by Francisco González-Galindo at the Instituto Astrofísica Andalucía.) GCMs are computer programs that model planetary atmospheres. They’re used all the time by weather forecasters on Earth, and planetary scientists have Martian versions as well, complete with accurate values for solar heating, winds, chemistry, cloud formation, and so on.

According to the GCM, nightglow on Mars is shaped by atmospheric tides. The gravity of the sun pulls on the Martian atmosphere, and the atmosphere has a natural response: It essentially rings like a bell three times a day. This accounts for the pulsating blobs around the equator.


Figure 6 of Schneider et al’s recent paper compares MAVEN data (panels a and b) to a GCM model of Martian nightglow (panel c).

“We were really impressed that the Mars General Circulation Model reproduced the equatorial patterns so well,” says Schneider. “The brightest spot hovers above the Martian prime meridian for months at a time, with two fainter spots placed on either side. Pulsating downdrafts at those locations boost the chemical reactions which give rise to nightglow.”

The model did not, however, account for the spiral. “We’ve really struggled to explain it,” he admits. “And however we might explain why a spiral should exist at the South Pole, we also need to explain why it should not exist at the North Pole!”

More data from MAVEN and updates to the Mars General Circulation Model might eventually provide an answer. For now, it remains a dizzying mystery.

Schneider et al‘s original research was just published in the August 6, 2020, edition of JGR Space Physics. Read it here.

Approaching Mars

Aug. 21, 2020: By the time you finish reading this sentence, you’ll be 40 km closer to Mars.

Earth and Mars are converging for a close encounter this Fall, one of the best since 2003, and their separation is rapidly shrinking–negative 8 km/s as of Aug. 21st. You are literally approaching the Red Planet. Just this week the brightness of Mars surpassed that of Sirius, the brightest star in the sky. Suddenly, Mars is almost bright enough to see in daylight and an easy target for backyard telescopes.

“Here is one hour of Mars rotating,” says amateur astronomer Maximilian Teodorescu of Magurele, Romania, who animated a sequence of photos taken Aug 18th using his 14-inch Newtonian:

“Lots of features are visible,” he says. “Note how the southern polar ice cap has contracted and broken–a result of it being late springtime on that side of Mars.”

The best is yet to come. By the night of closest approach on Oct. 6th (0.4149 AU), Mars will more than double in brightness again, outshining everything in the night sky except Venus and the Moon. Throughout this apparition, the south pole will remain tilted toward Earth, giving observers a good view of the breakup of the ice cap as Martian spring turns into summer.

Can’t wait? Right now, a good time to look is just before daybreak when Mars is high in the southern sky. Keep watching as twilight creeps up the sky. The planet’s burnt orange hue looks beautiful when surrounded by the day’s first hint of morning blue: sky map.

Congratulations, you’re now almost 500 km closer to the planet Mars.

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