The Changing Shape of Betelgeuse

Feb. 15, 2020: Betelgeuse isn’t just dimming, it’s also changing shape. Today, the European Southern Observatory released new images of Betelgeuse from the Very Large Telescope (VLT) in Chile’s Atacama desert. The unstable red supergiant is definitely lopsided:

A team led by Miguel Montargès of KU Leuven in Belgium took the picture in Dec. 2019, shortly after the star began its unprecedented dimming. They were able to compare it to a “normal” picture of Betelgeuse taken 11 months earlier. The change in shape is striking.

What’s going on? The researchers aren’t sure why Betelgeuse looks so different, but they suspect the involvement of dust. Red supergiants like Betelgeuse create and eject vast amounts of dusty material, losing mass even before they explode as supernovas. The lopsided shape and dimming of Betelgeuse might be explained if a cloud of dust is partially blocking its disk. Indeed, VLT infrared observations of Betelgeuse at the same time reveal lots of dust around the star:


Above: Clouds of dust around Betelgeuse. Credit: ESO/P. Kervella/M. Montargès et al. [more]

Mystery solved? Not necessarily. “Our knowledge of red supergiants remains incomplete, and this is still a work in progress, so a surprise can still happen,” notes Montargès. Other possibilities include magnetic activity on Betelgeuse’s surface (such as a giant starspot) and, of course, the early stages of a supernova explosion.

The Very Large Telescope with its adaptive optics instruments is one of the few facilities in the world capable of imaging the surface of Betelgeuse, located more than 600 light years away. More images from the Atacama desert may yet reveal what’s happening–if Betelgeuse doesn’t tell us first!

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The Problem with Satellite Mega-Constellations

Feb. 14, 2020: The night sky is in danger. This has been true for years as urban landscapes became increasingly light-polluted. But now there’s a new threat, one you can’t escape by driving into the countryside. It’s the “mega-constellation.” Some companies are planning to launch tens of thousands of internet satellites into low-Earth orbit. The recent launch by Space X of just 240 Starlink satellites has already ruined many astronomical observations.


Above: Astronomers at the Cerro Tololo Inter-American Observatory were trying to photograph nearby galaxies when 19 Starlink satellites intervened. [Full Story]

This week the International Astronomical Union (IAU) issued a new press release describing the impact of satellite mega-constellations on astronomy. IAU astronomers simulated 25,000 satellites similar in type to the satellites of SpaceX, Amazon, and OneWeb, and here are their results:

1. The number of satellites above the horizon at any given time would be between ~1500 and a few thousand. Most will appear very close to the horizon, with only a relative few passing directly overhead.

2. When the sun is 18 degrees below the horizon–that is, when the night becomes dark–the number of illuminated satellites above the horizon would be around 1000. These numbers will decrease during the hours around midnight when many satellites fall into Earth’s shadow.

3. At the moment it is difficult to predict how many of the illuminated satellites will be visible to the naked eye because of uncertainties in their reflectivity. Probably, the vast majority will be too faint to see. This depends to some degree on experiments such as those being carried out by SpaceX to reduce the reflectivity of their satellites with different coatings.

Trails made by Starlink satellites

Above: Starlink satellites photobomb the NGC 5353/4 galaxy group at Lowell Observatory [more]

4. Even if most satellites are invisible to the naked eye, mega-constellations pose a serious problem for professional astronomy. The trails of these satellites are bright enough to saturate modern detectors on large telescopes, and wide-field scientific astronomical observations will be severely affected.

5. The Vera C. Rubin Observatory currently under construction in Chile will be particularly hard-hit. The innovative observatory will scan large swaths of the sky, looking for near-Earth asteroids, studying dark energy, and much more. According to the IAU, up to 30% of the 30-second images during twilight hours will be affected. In theory, the effects of the new satellites could be mitigated by accurately predicting their orbits and interrupting observations, when necessary, during their passage, but this is a burdensome procedure.

There are no international rules governing the brightness of orbiting manmade objects. Until now, they didn’t seem to be necessary. Mega-constellations, however, threaten “the uncontaminated view of the night sky from dark places, which should be considered a non-renounceable world human heritage,” says the press release. Therefore the IAU will present its findings at meetings of the UN Committee for Peaceful Uses of Outer Space, bringing the attention of this problem to world leaders.

Surfing the Jet Stream Reduces Aviation Radiation

Feb. 12, 2020: Something strange is happening in the North Atlantic. For the past three years, airplanes have been flying across the ocean in record time. Credit the jet stream. It’s revved up, possibly by climate change, and planes that surf it are flying faster than ever before. The latest record was set just days ago. On Feb. 8, 2020, British Airways Flight 112 (BA 112) rocketed from New York to London in a mere 4 hours 56 minutes, at one point traveling faster than 825 mph.

This is good news, because airplanes surfing the jet stream absorb significantly less cosmic radiation.


(Top) The flight path of British Airways 112 and (Bottom) The transatlantic jet stream on Feb. 8, 2020.  Credit:

Researchers have long known that air travelers are exposed to cosmic rays. At typical cruising altitudes, passengers absorb 50 to 100 times more radiation than they would at sea level. This has led the International Commission on Radiological Protection (ICRP) to classify pilots and flight attendants as occupational radiation workers.

The jet stream can reduce this exposure. By propelling the passengers of BA 112 across the Atlantic at record speed, the jet stream lowered their radiation dose by about 30%. Two Virgin Atlantic flights following close behind the British Airways Boeing 747 experienced similar reductions.

These conclusions are based on E-RAD, a new model for aviation radiation. Since 2015, we ( and the students of Earth to Sky Calculus) have been collecting X-ray, gamma-ray, and neutron radiation data onboard airplanes. Our database contains more than 25,000 radiation measurements over 27 countries, 5 continents, and 2 oceans. E-RAD uses these measurements to predict dose rates on flights anywhere in the world.


British Airways flies from New York to London every day. We applied E-RAD to BA 112 on several dates, comparing dosages on Feb. 8th, when the plane surfed the jet stream, to nearby dates when it didn’t. Surfing the jet stream shaved almost 10 uSv (microSieverts) off the total radiation dose, a reduction equivalent to about 1 dental X-ray.

It’s not all good news, though. The jet stream can cause trouble. An active, fast-moving jet stream is often filled with turbulence, making flights miserable for buckled-in passengers. Planes dodging the rough air can actually increase their flight times, boosting cosmic ray exposure instead of reducing it.

Oh, and did you want to go home? Passengers returning to New York from London have to cross the Atlantic against the jet stream. Their flights will be slower, increasing exposure time. Indeed, we calculated the radiation exposure for British Airways flight 177 on Feb 8th, which flew in the opposite direction, from London to New York. Passengers onboard that aircraft received double the dosage: 34.4 uSv (London to New York) instead of the 17.7 uSv (New York to London) received by passengers on the BA 112 flight earlier in the day.

Climate change research suggests that all of these effects will intensify in the years ahead. A seminal study in 2016 found that changes in atmospheric dynamics would increase round-trip times between London and New York despite the quickening jet stream. Unless you fly to London and remain there, you’re going to absorb more and more “rads on a plane.”

End Notes:

(1) The radiation dosages mentioned in this story are not dangerous. Typically, they amount to 2 or 3 dental X-rays spread out over hours instead of the quick, intense pulse you receive in a dentist’s office. A single flight is not going to kill you. For frequent flyers and flight crews, however, repeated exposure adds up over time and may pose health risks that are still poorly understood.

(2) Transatlantic flights have been breaking records for the past three years. In Jan. 2018, a Norwegian passenger jet set a record when it went 779 mph during a trip from New York to London. In Feb. 2019, Virgin Atlantic went even faster: 801 mph from Los Angeles to London. Then, on Feb. 8, 2020, a British Airways Flight 112 shattered those records: 825 mph from New York to London.

(3) A key article on this topic is Transatlantic flight times and climate change. Environmental Research Letters, 2016; 11 (2): 024008 DOI: 10.1088/1748-9326/11/2/024008

According to the study, led by Dr Paul Williams, an atmospheric scientist at the University of Reading, “the average jet-stream winds along the flight route between London’s Heathrow airport and New York’s John F. Kennedy International airport are predicted to become 15% faster in winter, increasing from 77 to 89 km/hr (48 to 55 mph), with similar increases in the other seasons. As a result, London-bound flights will become twice as likely to take under 5h 20m, implying that record-breaking crossing times will occur with increasing frequency in future. On the other hand, New York-bound flights will become twice as likely to take over 7h 00m, suggesting that delayed arrivals will become increasingly common.”


Prediction: Betelgeuse Could Bounce Back

Feb. 9, 2020: For months, astronomers have been keeping a wary eye on Betelgeuse, the bright red star in Orion’s shoulder. What’s attracting their attention? All of a sudden, Betelgeuse isn’t bright anymore. Its visible luminosity has “fallen off a cliff”–a sign that the star could be on the verge of going supernova.

“The most recent measurements put the visual magnitude of Betelgeuse at about +1.66, the dimmest its been in our 25 years of photometry,” says Edward Guinan of Villanova University.

Above: The horizontal axis is Heliocentric Julian Date (HJD). For reference, Jan. 30, 2020, the date of the most recent measurement, has an HJD of 2458879.

Betelgeuse is a highly evolved red supergiant–the type of star that could collapse and explode at any moment. Indeed, the dimming of Betelgeuse could be explained if the star has suddenly contracted to about 92% of its previous radius. But that’s not the only possibility. Betelgeuse might be dimmed by a giant starspot–or maybe it is shrouded by an outburst of stardust from its own cool outer layers–or something else entirely. No one knows.

Answers might be forthcoming on Feb. 21st. Astronomers have long known that Betelgeuse is a variable star. It pulsates with many periods, as shown in this Fourier analysis of Betelgeuse’s light curve:

Above: A period analysis of 23 years (1995-2018) of Betelgeuse photometry. Credit: Peranso.

“This shows a dominant (probable pulsation) period of P = 430 days,” note Guinan and colleague Richard Wasatonic in a recent Astronomical Telegram. Given this result, “the minimum brightness is expected on 21 (+/-7d) February 2020.”

If Betelegeuse starts to bounce back on Feb. 21st, this whole episode might just be a deeper-than-average pulsation, and perhaps the supernova watch can be called off. However, notes Guinan, “even if the 430-day period is still working, this would indicate a minimum brightness near 0.9 mag–much brighter than the current value near 1.6 mag. So something very unusual is going on.”

Stay tuned for updates as Feb. 21st approaches.

High-altitude Balloon Photos of Polar Stratospheric Clouds

Feb. 4, 2020: On Jan. 22, 2020, something lucky happened. and the students of Earth to Sky Calculus were inside the Arctic Circle, preparing to launch a cosmic ray balloon. Moments before liftoff, an outbreak of Type 2 polar stratospheric clouds (PSCs) started developing over the launch site. PSCs are very rare. They form in the stratosphere only when the air temperature drops to a staggeringly-cold -85C. And they are extremely difficult to catch. Working quickly, we launched two balloons directly into the outbreak.


Operating 4 cameras, the two balloon payloads photographed the clouds from altitudes as high as 75,000 feet. We believe this is the first time polar stratospheric clouds have been photographed by a high-altitude balloon from their own habitat–the stratosphere. The footage reveals beautiful filamentary structures previously unseen from the ground.

How did we get so lucky? We had some help from the polar stratospheric vortex.

The polar stratospheric vortex is a jet stream in the Arctic stratosphere. This winter it has been very strong, bottling up cold air and preventing it from spilling to lower latitudes.  Just before we launched on Jan. 22nd, something unexpected happened to the polar vortex. It became elliptical and rotated around, sloshing a mass of super-cold stratospheric air over northern Scandinavia.

This is what the vortex looked like on Jan. 22-23, according to NASA’s Microwave Limb Sounder (MLS):


Note the purple blob over northern Sweden. That’s the cold air. PSCs can form inside the white contours. This animation of MLS data created by Lynn Harvey of the University of Colorado’s Laboratory for Atmospheric and Space Physics shows how the vortex evolved during our time in Sweden.

Type 2 polar stratospheric clouds are widely regarded as the most beautiful clouds on Earth. They are made of tiny ice crystals that diffract high-altitude sunlight, glowing with colors so vivid that some people mistake them for “daytime auroras.” Earth to Sky student Jordan Herbst’s photos of the Jan. 22-23 outbreak show how they look from the ground.  Now we know they’re beautiful from the stratosphere, too.

Stay tuned for more news from our trip to the Arctic Circle.

A New Form of Auroras: “The Dunes”

Jan. 29, 2020: A new type of aurora is rippling across Arctic skies. Citizen scientists who discovered it nicknamed it “The Dunes” because of its resemblance to desert sand dunes. A paper published in the Jan. 28th issue of AGU Advances describes the new form and the unexpected physics that causes it.


Above: Aurora dunes over Laitila, Finland, on Oct. 7, 2018. Credit: Pirjo Koski. [more]

Dune-shaped auroras form in a narrow altitude range 80 km to 120 km above Earth’s surface. Turns out, this is an extremely hard-to-study layer of Earth’s atmosphere. It’s too high for weather balloons, and too low for rockets.

“Due to the difficulties in measuring atmospheric phenomena between 80 and 120 km, we sometimes call this region ‘the ignorosphere‘,” says Minna Palmroth, Professor of Computational Space Physics at the University of Helsinki and the lead author of the study.

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 the dunes from widely separated locations in Finland. Maxime Grandin, a postdoctoral researcher in Palmroth’s team, analyzed the images, using triangulation techniques to decipher the Dune’s geometry.

Conclusion: Dunes are located ~100 km high–smack-dab in the middle of the ignorosphere–and have a pure, monochromatic wavelength of about 45 km.


Above: An artists’ concept of a mesospheric bore trapped in a high-altitude waveguide. [more]

The research team believes the Dunes are a “mesospheric bore”–a type of atmospheric gravity wave that springs up from the surface below and gets caught in a thermal waveguide ~100 km high. When solar wind particles rain down on the bore, they illuminate its rippling structure.

The discovery of Dunes may allow researchers to study the ignorosphere as never before. Monitoring Dunes can reveal previously hidden waves and waveguides at the boundary between Earth and space. Aurora photographers, have you seen a Dune? Submit your photos here.

Note: This research was made possible by ordinary people paying close attention to the sky. The first report of aurora dunes in Oct. 2015 came from Mikko Peussa, an aurora photographer in Finland. Next, Matti Helin learned of the phenomenon and managed to get researchers interested. Helin participated in subsequent breakthrough observations, and joined 6 other amateurs (P. Koski, A. Oksanen, M. A. Glad, R. Valonen, K. Saari and E. Bruus ) on the AGU Advances paper.

Magnetic Explosions Discovered on Earth’s Doorstep

Jan. 16, 2019: Yes, there are explosions in Earth’s magnetic field. They happen all the time. Gusts of solar wind press against Earth’s magnetosphere, squeezing lines of magnetic force together. The lines criss-cross and reconnect, literally exploding and propelling high energy particles toward Earth.  Auroras are the afterglow of this process.

On Dec. 20, 2015, one such explosion occurred closer to Earth than anyone had seen before.  It has taken researchers 4 years to fully wrap their minds around what happened, and the results were published just this week in the Jan. 13, 2020, edition of Nature Physics.


Auroras in the aftermath of a near-Earth magnetic explosion on Dec. 20, 2015. Credit: Joseph Bradley of Whitehorse, Yukon, Canada

Lead author Vassilis Angelopoulos of UCLA explains: “Usually, these explosions happen at least 100,000 miles from Earth, far downstream in our planet’s magnetic tail. On Dec. 20, 2015, however, we observed a reconnection event only 30,000 miles away–more than 3 times closer than normal.”

It was a case of good luck and perfect timing. NASA’s swarm of three THEMIS spacecraft were passing through the area, and they were able to pinpoint the explosion’s location “right on the doorstep” of the geosynchronous satellite belt. This showed reconnection events may pose a previously overlooked threat to Earth-orbiting satellites. The nearby blast caused a strong G2-class geomagnetic storm and intense auroras around the Arctic Circle.


In this diagram of Earth’s magnetosphere, “X” marks the spot of the Dec. 20, 2015, explosion. The 3 THEMIS spacecraft are also shown. Credit: Emmanuel Masongsong, UCLA EPSS

Angelopoulos estimated the energy involved. “The explosion and subsequent storm delivered as much as ~88 PetaJoules of energy to the near-Earth environment. That’s more than 10 times the energy of the largest US nuclear bomb and about 20 times the energy of a magnitude 7 earthquake.”

Before this event, many researchers felt that reconnection at such proximity was impossible. Earth’s nearby magnetic field was too stable for such explosions … or so the thinking went.

“Now we know better,” Angelopoulos says. “The THEMIS multipoint observations are iron-clad. It really happened, and this is going to make a big impact on future studies of geomagnetic storms.”

The original research in Nature Physics may be found here.


The Fainting of Betelgeuse — Update

Jan. 10, 2020: One day, perhaps in our lifetimes, perhaps a million years from now, the red giant Betelgeuse will dim a little–and then explode. The resulting supernova will rival the full Moon and cast shadows after dark, completely transforming the night skies of Earth. No wonder astronomers are closely tracking the current “fainting of Betelgeuse.”

“Fainting” is an actual astronomical term. It means dimming, the opposite of brightening. And right now, Betelgeuse is definitely fainting.


Betelgeuse photographed by Brian Ottum of Animas, New Mexico, almost 4 years apart using the same telescope and observing methods.

Edward Guinan of Villanova University and colleagues caused a minor sensation last month when they reported “[Betelgeuse] has been declining in brightness since October 2019, now reaching a modern all-time low of V = +1.12 mag on 07 December 2019 UT. Currently this is the faintest the star has been during our 25+ years of continuous monitoring.”

Little did they know when they issued their telegram in December that Betelgeuse was about to become even fainter. “On 06 January 2020 UT, the magnitude of Betelgeuse was V = +1.37,” reports Guinan. That’s 20% dimmer than the “modern all-time low” registered last month.

This 3-year plot of the Villanova team’s data shows Betelgeuse’s rapid decline:


The horizontal axis is Heliocentric Julian Date (HJD). For reference, Jan. 6, 2020, the date of the most recent measurement, has an HJD of 2458855.

The fainting is easy to see with the naked eye. Not too long ago, Betelgeuse was the 10th brightest star in the sky. Now it is the 21st. Observers of Orion rising in the east after sunset can’t help but notice that the Hunter’s shoulder is dimmer than it used to be.

Astronomers have long known that Betelgeuse is on the precipice of an energy crisis. It’s about to run out of fuel in its core. When that happens, the star will collapse and rebound explosively, producing the first bright supernova in the Milky Way since 1604. Experts in stellar evolution believe Betelgeuse could die at any time during the next 100,000 years or so–a blink of an eye on time scales of astronomy.

Does the current dimming herald that final blast? Probably not. Betelgeuse is a slowly variable star, and this is probably no more than an episode of deeper-than-usual dimming. Of course, one day astronomers will think the same thing … and then the night sky will change forever.

Stay tuned for updates.

Polar Stratospheric Clouds Continue

Jan. 9, 2020: The finest outbreak of polar stratospheric clouds (PSCs) in decades is still going strong. “We witnessed a wonderful display this evening (Jan. 8th),” reports Alex Conu, who photographed the clouds drawing a crowd in Oslo, Norway:


“The cloud’s bright pastel colors looked fabulous alongside Venus in the evening sky,” he says.

Polar stratospheric clouds are rare. Normally, the stratosphere has no clouds at all. A few times each winter, however, icy clouds form when the temperature in the stratosphere drops below -85C. Such staggeringly-low temperatures are required to help sparse water molecules stick together. This winter, the clouds have been appearing daily since late December, a sign of unusually cold conditions in the stratosphere.

Stratospheric clouds are widely regarded as the most beautiful clouds on Earth. Because of their intense colors (caused by high-altitude sunlight hitting tiny ice crystals), novice sky watchers sometimes mistake the clouds for auroras. This picture from P-M Hedén of Tänndalen, Sweden, shows why:


“On Jan. 4th, the colors got so strong that the snow turned red,” marvels Hedén. “I have been seeing these crazy displays at both sunrise and sunset from my cabin in the Swedish mountains.”

Stay tuned for updates as the outbreak continues.

Electricity Surges Through the Soil of Norway

Jan. 7, 2019: Yesterday, Jan. 6th, something unexpected happened in the soil of northern Norway. “Electrical currents started flowing,” reports Rob Stammes, who monitors ground currents at the Polarlightcenter geophysical observatory in Lofoten. This chart recording shows the sudden surge around 1930 UT:

“It seemed to be some kind of shockwave,” says Stammes. “My instruments detected a sudden, strong variation in both ground currents and our local magnetic field. It really was a surprise.”

NASA’s ACE spacecraft detected something as well. About 15 minutes before the disturbance in Norway, the interplanetary magnetic field (IMF) near Earth abruptly swung around 180 degrees, and the solar wind density jumped more than 5-fold. Earth may have crossed through a fold in the heliospheric current sheet–a giant, wavy membrane of electrical current rippling through the solar system. Such crossings can cause these kind of effects.

While currents flowed through the ground, auroras filled the sky. Rayann Elzein photographed the corresponding outburst of lights from Utsjoki, Finland:

“What a surprise!” says Elzein. “The auroras were sudden and dynamic, with fast-moving green needles and several purple fringes!”

The auroras and ground currents were caused by the same thing: Rapidly changing magnetic fields. High above Earth’s surface, magnetic vibrations shook loose energetic particles, which rained down on the upper atmosphere, creating auroras where they struck. Just below Earth’s surface, magnetic vibrations caused currents to flow, triggering Rob Stammes’ ground sensors.

“We couldn’t see the auroras in northern Norway because of cloud cover,” says Stammes, a little ruefully. “We had to be satisfied with the electricity underfoot.”

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