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 https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2020AV000183.

Bright Comet Erasmus

Nov. 21, 2020: Every 2000 years, Comet Erasmus (C/2020 S3) visits the inner Solar System. News Flash: It’s back.┬áDiscovered 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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