Nov. 20, 2023: There’s a new phenomenon in the night sky: “SpaceX auroras.” They’re red, roughly spherical, and brightly visible to the naked eye for as much as 10 minutes at a time. “We are seeing 2 to 5 of them each month,” reports Stephen Hummel of the McDonald Observatory in Texas, who photographed this one on Nov. 3rd:

Spoiler alert: They’re not auroras. The bright red balls are caused by SpaceX rockets burning their engines in the ionosphere.

The phenomenon is closely related to something we reported earlier this year. Falcon 9 rockets leaving Earth can “punch a hole in the ionosphere.” The ionosphere is a layer of ionized gas surrounding our planet; it is crucial to over-the-horizon shortwave radio communication and can affect the quality of GPS signals. Water-filled rocket exhaust can quench local ionization by as much as 70%, erasing the ionosphere along the rocket’s path. For reasons having to do with chemistry, ionospheric holes emit a red glow (630 nm).

“SpaceX auroras” are exactly the same–except instead of rockets going up, they are caused by rockets coming down. The second stage of the Falcon 9 rocket burns its engines in order to de-orbit and return to Earth, creating an ionospheric hole as it descends.

“We first noticed these SpaceX de-orbit burns over the McDonald Observatory in February 2023,” says Boston University space physicist Jeff Baumgarder, who has been studying ionospheric holes for more than 40 years. “The engine burns are only about 2 seconds long, just enough delta V to bring the second stage down over the south Atlantic Ocean.  These burns happen ~90 minutes ( ~one orbital period) after launch.  During the burn, the engine releases about 400lbs of exhaust gasses, mostly water and carbon dioxide.  All this happens at ~300km altitude, near the peak of the ionosphere, so a significant hole is made.”

“The resulting ‘auroras’ can be very bright, easily visible with the naked eye and much brighter than Starlink satellites themselves, although only for a few seconds,” notes Hummel.

The question is, are SpaceX auroras good or bad?

Hummel is the McDonald Observatory Dark Skies Sr. Outreach Program Coordinator, so naturally he’s concerned about the effect these events may have on observational astronomy.

“The frequency of these red clouds could increase as SpaceX targets more launches in the future,” says Hummel. “Their impact on astronomical science is still being evaluated. Starlink satellites are a known issue, but the effects of the rocket launches themselves are a growing area of attention.”

For Jeff Baumgarder, who has his own dedicated camera at McDonald, the events are a golden opportunity for research.

“The saying ‘one person’s signal is another person’s noise’ is appropriate here,” says Baumgardner. “We are delighted with the rocket burns. They give us an opportunity to explore how space traffic affects the ionosphere. The ionospheric density is different night to night, so we can learn something about the efficiency of the chemistry by observing many events.”

Other sky watchers are beginning to see SpaceX auroras as well. Are you one of them? Submit your pictures here.

Nov. 14, 2023: (Spaceweather.com): A phenomenon rarely seen in centuries might have just appeared in the night sky over Colorado–a “Bright Night.” Philosophers and scientists have reported Bright Nights for literally thousands of years. It’s when an otherwise dark and moonless night fills with a soft glow, allowing observers to see distant mountains or read a newspaper. Pliny the Elder, an Army commander in ancient Rome, described the phenomenon as a “nocturnal sun” (~ 113 BCE).

In the modern world, Bright Nights are seldom seen. Most of our planet’s human population lives in cities, and even rural landscapes are somewhat lit by distant urban bulbs. The “nocturnal sun” has been overwhelmed.

Or has it? Enter Aaron Watson, an experienced night-sky photographer who regularly visits the darkest of dark-sky sites in remote parts of Colorado. On multiple occasions this year he has photographed red auroras and green airglow invisible from any ordinary countryside. Last month, he was at one of his favorite inky-dark sites when he may have experienced a modern Bright Night.

Above: Bright airglow over Colorado on Oct. 9, 2023. Credit: Aaron Watson

“I go outside on most clear nights to observe,” says Watson, “but the night of Oct 9th was noticeably different. Although there was no Moon, or any other source of light, the landscape was softly illuminated. Nearby juniper trees made dark silhouettes against the glowing night sky. I could easily see my telescope and equipment. My partner was with me, and I could see her face quite well. I remarked, ‘Wow, it’s so bright out!’ and she agreed.”

“A ‘Bright Night’ sounds exactly like what I experienced!” says Watson.

As the landscape grew in brightness, Watson decided to photograph the sky. When he pointed his lens toward the stars, the viewscreen of his camera filled with green light. “It was a very strong green airglow–perhaps the brightest I have ever seen,” he says. A 20 second exposure produced the photo shown above.

Bright Nights have been a mystery since at least the first century. Watson’s photo could be a clue. It seems to confirm a hypothesis published in 2017 by Gordon Shepherd, then a professor at Canada’s York University, who believed that Bright Nights were caused by intense displays of airglow.

Shepherd came to this conclusion using a satellite sensor he built himself: The Wind Imaging Interferometer (WINDII), which orbited Earth for 14 years onboard NASA’s Upper Atmosphere Research Satellite. When he and co-author Youngmin Cho examined WINDII’s archive, they found a number of apparent Bright Nights in the sensor’s airglow data.

Airglow is just what it sounds like: A diffuse glow that fills the air. It is produced by photochemistry in Earth’s upper atmosphere, with its green color coming from atomic oxygen. Frequently photographed by astronauts on the ISS, airglow can be detected by sensitive cameras on almost any dark night from all locations on Earth. Rarely, however, is it visible without a camera.

Airglow seen from the International Space Station

In their paper, Shepherd and Cho highlighted 11 events where WINDII detected airglow bright enough to see with the human eye. All were correlated with giant waves of high-altitude air called “zonal waves.”  Zonal waves are linked to Earth’s jet stream, and play a crucial role in weather and climate. During the events Shepherd and Cho studied, zonal waves piled up (“constructively interfered”) to create high pressure regions hundreds to thousands of miles wide. By forcing atomic oxygen into a higher concentration, the zonal waves created an intense Bright Night glow.

The amorphous glow in Watson’s photo is just what one would expect of broad zonal wave activity. “The airglow was strong in all directions,” recalls Watson. “It had a flat color density without ripples or other fine structures”–just as one would expect from Shepherd and Cho’s  hypotheses. 

Bright Nights might not be a thing of the past, after all.

Would you like to experience a Bright Night? Good news: Solar activity is boosting airglow, making the job of zonal waves that much easier. On the next moonless night, find a dark-dark site far from city lights. Bring a newspaper to read–and let us know what happens.

Nov. 6, 2023: (Spaceweather.com) During this past weekend’s strong G3-class geomagnetic storm, low-latitude auroras spread as far south as Texas and Arizona. Upon further review, most of those lights were not auroras at all. Everything red in this montage is an “SAR arc”:

Credits: Texas (Anita Oakley); Missouri (Dan Bush); New York (James Perez-Rogers); Arizona (Jeremy Perez)

“This was a new phenomenon to me,” says Jeremy Perez, who took the Arizona picture. “I had never heard of SARs before, but I kept shooting anyway.”

SAR arcs were discovered in 1956 at the beginning of the Space Age. Researchers didn’t know what they were and unwittingly gave them a misleading name: “Stable Auroral Red arcs” or SAR arcs. In fact, SAR arcs are neither stable nor auroras.

Auroras appear when charged particles rain down from space, hitting the atmosphere and causing it to glow. SAR arcs form differently. They are a sign of heat energy leaking into the upper atmosphere from Earth’s ring current system–a donut-shaped circuit carrying millions of amps around our planet.

An artist’s concept of Earth’s ring current, quiet (left) and active (right) [more]

“On Nov. 5th, the ring current was pumped up by hours of strong geomagnetic storming, with energy dissipating into these SAR arcs,” says Jeff Baumgardner of Boston University’s Center for Space Physics. “It was a global event. Our cameras registered SAR arc activity from Italy to New Zealand.”

Recent research has linked SAR arcs to another phenomenon that is not an aurora: STEVE. The mauve ribbon in the sky was not originally thought to have anything to do with Earth’s ring current. Yet in 2015, observers in New Zealand caught a bright red SAR arc transforming itself into STEVE like a caterpillar into a butterfly.

On Nov. 5th, Mark Savage may have witnessed the same metamorphosis over Northumberland, UK:

Visible to the naked eye, STEVE materialized from an overhanging red arc. “The entire process took about 10 minutes,” says Savage. This timescale roughly matches that of another SAR-to-STEVE transition observed over Canada in April 2022. Clearly, the two phenomena are linked, but researchers aren’t sure how.

“The connection is still elusive,” says Carlos Martinis, a leading researcher in the field at Boston University. “Sometimes SAR arcs evolve into STEVE–but not always. This is a very active field of research, involving citizen scientists and researchers.”

Did you see an SAR arc on Nov. 5th? Submit your pictures here.

more SAR images: from Greg Redfern of Shenandoah National Park, Virginia; from Dean Cosgrove near Stockville, Nebraska; from Chris Cook of Borrego Springs, California; from Todd Bush of Banner Elk, North Carolina; from Ronnie Sherrill of Troutman, North Carolina; from George Preoteasa of Milford, PA; from David Blanchard of Wupatki National Monument, Arizona; from Hunter Outten of Laurel, Delaware; from Caryl Bohn of West Oak, Nebraska; from Ken Sklute of Phoenix, Arizona; from Bernhard Deufel of Horgen, Switzerland; from Klaus Steinberg of Troisdorf, Germany; from Bernhard Deufel of Horgen, Switzerland