A Major Outbreak of Noctilucent Clouds

July 6, 2020: Last night, July 5-6, a major outbreak of noctilucent clouds (NLCs) blanketed Europe. Electric-blue tendrils of frosted meteor smoke rippled over almost every European capital from Scandinavia to the Adriatic. “It was the most phenomenal display of NLCs I’ve seen in my life,” says Viktor Veres, who photographed the outbreak from Budapest, Hungary:

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“I was just getting ready for dinner when one of my friends, Alex, cried ‘NLC party time!’,” says Veres. “The electric-blue clouds were almost directly overhead. I sprinted to the car (partially dressing in the street) and drove up Gellért Hill for a view of the clouds over the most famous sights of Budapest–the Danube River, Chain Bridge, Buda Castle, and Parliament. And, yes, my dinner got cold.”

Paris was also “overcast” by noctilucent clouds. “They were very bright,” reports Bertrand Kulik, who shot them floating above the Eiffel Tower:

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“The shapes of the noctilucent waves were out of this world!” he says.

NLCs are Earth’s highest clouds. Seeded by meteoroids, they float at the edge of space 83 km above the ground. The clouds form during summer when wisps of water vapor rise up to the mesosphere, allowing water to crystallize around specks of meteor smoke. This summer, record cold temperatures in the mesosphere are boosting their production.

Last night’s mega-display in Europe comes on the heels of a 4th of July sighting in southern California at the same latitude as Los Angeles. It seems that everyone should be alert for noctilucent clouds. Dusk and dawn are the best times to look; here’s why.

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The Invisible Lunar Eclipse

July 4, 2020: The Moon is about to pass through the shadow of Earth, producing a penumbral lunar eclipse. Unfortunately, it might be invisible.

Eclipse expert Fred Espenak explains: “During past lunar eclipses, I have made a concerted effort to determine when I can first see the subtle shading of Earth’s penumbral shadow on the Moon (using naked eye and binoculars). I have consistently found the penumbral shading is only detectable when at least 2/3 of the Moon lies within the penumbral shadow.”

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“Because the Moon will only pass 1/3 of the way into Earth’s penumbral shadow during the July 4/5 lunar eclipse, it will NOT BE VISIBLE to the naked eye,” he says.  “Digital photography can reveal the subtle shading if the contrast of the image is greatly increased.

Penumbral eclipses differ from total eclipses as follows: In a total lunar eclipse, the Moon passes directly through the darkest crimson-colored core of Earth’s shadow. It produces a “Blood Moon.” In a penumbral lunar eclipse, the Moon passes through the pale outskirts of Earth’s shadow. Penumbral eclipses are notoriously subtle–and in this case potentially invisible.

“I fear the general media is hyping this event when there’s really nothing more to see than a Full Moon–although that’s beautiful in its own right,” he says.

The Rapid Brightening of Comet NEOWISE

June 30, 2020: Comet NEOWISE (C/2020 F3) is passing by the sun this week–and it’s looking good. The comet just experienced a sharp increase in brightness recorded by coronagraphs onboard the Solar and Heliospheric Observatory (SOHO). Click to play a 4-day movie of the surge:

Bum-Suk-Yeom-20200622_0627_c3_Comet_C2020F3_NEOWISE_bsyeom_1593387415

“During the transit, Comet NEOWISE increased in brightness from magnitude +4 to +1.8–an almost 8-fold jump,” says planetary scientist Qicheng Zhang of Caltech, who analyzed the images. “If the comet maintains this brightness, it will be visible to the naked eye when it emerges from the sun’s glare in July.”

Zhang is a bit concerned, however, that the rapid brightening might be too much of a good thing. “When a comet brightens this quickly (2.2 magnitudes in only ~4 days) it could be a sign that the nucleus is unstable. Comet NEOWISE might yet disintegrate,” he cautions.

Among astronomers, this is a bit of a sore point. Earlier this year two comets, ATLAS (C/2019 Y4) and SWAN (C/2020 F8), approached the sun with much fanfare, then disintegrated before they could become naked-eye objects. Disappointing.

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The disintegration of Comet ATLAS when it passed by the sun at a similar distance in April 2020. Credit: Hubble Space Telescope. [More]

Will Comet NEOWISE end the same way?

“I don’t think so,” says Karl Battams of the Naval Research Lab in Washington DC. “Comet NEOWISE looks healthy to me. It showed a smooth-and-steady brightness increase, perhaps a little steeper than we might like, but nothing that makes me enormously concerned for its health, as long as it has a reasonably large nucleus.”

We’ll soon find out. “Later this week, around perihelion (closest approach to the sun) the comet may be observable by skilled astronomers low in the morning twilight,” says Zhang. “If it maintains anything close to its brightness as it left SOHO’s field of view, it will most likely be recovered from the ground by then.”

Any sightings this week could be very good news, indeed. As July unfolds, the comet will swing around the sun and pop up in the evening sky–perfectly placed for casual sky watchers if anything remains to be seen.  Stay tuned for updates.

Out of Nowhere, a Global Magnetic Anomaly

June 25, 2020: Lately, Earth’s magnetic field has been quiet. Very quiet. The sun is in the pits of what may turn out to be the deepest Solar Minimum in a century. Geomagnetic storms just aren’t happening.

“That’s why I was so surprised on June 23rd when my instruments picked up a magnetic anomaly,” reports Stuart Green, who operates a research-grade magnetometer in his backyard in Preston UK. “For more than 30 minutes, the local magnetic field oscillated like a sine wave.”

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This chart recording shows a magnetic wave rippling through Preston UK on June 23, 2020. Credit: Stuart Green.

Green quickly checked solar wind data from NOAA’s DSCOVR satellite. “There was nothing–no uptick in the solar wind speed or other factors that might explain the disturbance,” he says.

He wasn’t the only one who noticed. In the Lofoten islands of Norway, Rob Stammes detected a similar anomaly on his magnetometer. “It was remarkable,” he says. “Our magnetic field swung back and forth by about 1/3rd of a degree. I also detected ground currents with the same 10 minute period.”

What happened? Space physicists call this phenomenon a “pulsation continuous” or “Pc” for short. Imagine blowing across a piece of paper, making it flutter with your breath. Solar wind can have a similar effect on magnetic fields. Pc waves are essentially flutters propagating down the flanks of Earth’s magnetosphere excited by the breath of the sun. During more active phases of the solar cycle, these flutters are easily lost in the noise of rambunctious geomagnetic activity. But during the extreme quiet of Solar Minimum, such waves can make themselves “heard” like a pin dropping in an silent room.

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Magnetic observatories around the world detected the wave on June 23, 2020. Credit: INTERMAGNET

Earth’s magnetic field was so quiet on June 23rd, the ripple was heard all around the world. INTERMAGNET‘s global network of magnetic observatories picked up wave activity at the same time from Hawaii to China to the Arctic Circle. There’s even a hint of it in Antarctica.

Pc waves are classified into 5 types depending on their period. The 10-minute wave on June 23rd falls into category Pc5. Slow Pc5 waves have been linked to a loss of particles from the van Allen radiation belts. Energetic electrons surf these waves down into Earth’s atmosphere, where they dissipate harmlessly.

With Solar Minimum in full swing, there’s never been a better time to study these waves. Keep quiet … and stay tuned for more.

 

Noctilucent Clouds over London

June 23, 2020: On June 21st, something rare and magical happened in London. The skies of the great city filled with noctilucent clouds (NLCs). Phil Halper noticed the display, grabbed a camera, and raced from one landmark to another, hurriedly recording pictures like this:

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“Even the bright lights of the London Eye on the river Thames couldn’t drown out the display,” says Halper. “These were the most spectacular NLCs I’ve ever seen.”

If NLCs look alien–that’s because they are. The clouds are seeded by meteoroids. They form every year around this time when summertime wisps of water vapor rise up to the mesosphere, allowing water to crystallize around specks of meteor smoke.

Usually you have to be under a dark sky at high latitudes to see these rare clouds–but 2020 is not usual. Record-cold temperatures in the mesosphere are boosting NLCs, brightening them enough to see from places like London.

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Halpert is a longtime observer of NLCs, and when he saw their electric-blue ripples forming over the city, he immediately realized it was a special occasion. “I hired a bike and cycled from landmark to landmark, stopping at the London Eye, the Tower of London, Blackfriar’s Bridge, St. Paul’s Cathedral and Temple,” he says. “I had to hurry because there is only about one hour of night when the NLCs are visible.’

“Alas, in the rush, I fell off my bike and I ended up in hospital,” he says. “But still it was well worth it. I was thrilled to see this magical display.” (Thank you, Phil!)

The outbreak over London is a sign that even more intense NLCs could be on the way. Last summer, bright noctilucent clouds over European capitals heralded a descent to even lower latitudes. Indeed, just this morning sky watchers in Oregon witnessed their own outbreak. James W. Young sends this picture from Seaside, OR:

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“The NLCs were incredibly intense on the morning of June 23rd,” says Young. “I was able to take this picture using just a 1/4-second exposure (ISO 800).”

Observing tips: The best time to look for noctilucent clouds is during the hours after sunset (or before sunrise) when the sun is at least 6 degrees below the horizon: diagram. If you see electric-blue tendrils spreading across the sky … submit your photos here!

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Naked-Eye Comet NEOWISE?

June 15, 2020: Here we go again. A comet is falling toward the sun, and it could become a naked-eye object after it skims past the orbit of Mercury on July 3rd. Michael Mattiazzo photographed Comet NEOWISE (C/2020 F3) on June 10th from Swan Hill, Australia:

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“Pushing the limits of comet observing, I had to leave home to find a clear horizon,” says Mattiazzo. “When I took the picture, Comet NEOWISE was very close to the sun and only 5 degrees above the local horizon. Its visual magnitude was near +7.0, below the threshold for naked-eye visibility.”

It might not look like much now, but this comet could blossom in the weeks after perihelion (closest approach to the sun). Forecasters say Comet NEOWISE could become as bright as a 2nd or 3rd magnitude star. Northern hemisphere observers would be able to easily see it in the evening sky in mid-July.

At this point, readers may be experiencing a feeling of déjà vu. Almost the exact same forecast was issued for Comet ATLAS (C/2019 Y4) in March and Comet SWAN (C/2020 F8) in May. Both comets dived toward the sun and … instead of blossoming, died. Intense solar heat can do that to a fragile ball of ice.

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Planets, comets, and asteroids transiting SOHO’s C3 coronagraph in 2020. Comet NEOWISE is marked by a red arrow.

Mattiazzo, who is one of the world’s most experienced amateur comet observers, thinks Comet NEOWISE could turn out better. “I’d say there’s a 70% chance this comet will survive perihelion,” he says, basing his guess on the stability of the comet’s light curve, which sets it apart from Comets ATLAS and SWAN. “Comet NEOWISE could be a case of third time lucky.”

We’ll know soon enough. On June 22nd, the comet will enter the field of view of SOHO‘s C3 coronagraph–a space-based instrument that blocks the glare of the sun to reveal nearby stars, planets and comets. For a whole week, astronomers will be able to monitor Comet NEOWISE as it approaches the orbit of Mercury. If it falls apart, the event may be visible in the images. Ditto if it survives.

Stay tuned for updates.

Record Cold in the Mesosphere

June 9, 2020: It’s getting cold in the mesosphere. Very cold. “At polar latitudes (60N-80N) temperatures have been breaking 14-year records in the last few days,” reports Lynn Harvey of the University of Colorado Laboratory for Atmospheric and Space Physics.  This development is causing noctilucent clouds (NLCs) to spill out of the Arctic to middle latitudes.

“I’ve been waiting for years to see NLCs, and finally it happened!” reports Phil Halpert from London, England, on June 7th. He noticed their electric-blue ripples over local rooftops, then rushed out to photograph them in open sky over Clissold Park:

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“This is the first time I have ever seen noctilucent clouds over London!” he says.

NLCs are Earth’s highest clouds. Seeded by meteoroids, they float at the edge of space 83 km above the ground. The clouds form when summertime wisps of water vapor rise up to the mesosphere, allowing water to crystallize around specks of meteor smoke. Usually they are best seen after the summer solstice, but this year they are getting an early start.

What’s happening? To find out, Harvey has been looking at data from NASA’s Microwave Limb Sounder (MLS), which can sense conditions 83 km high where NLCs form. “These plots show that 2020 is shaping up to be a cold and wet year in the mesosphere,” she says.

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“Temperatures, in particular, are very cold,” she says. “In fact, mid-latitude temperatures (35N-55N) in late May (DOY 142-148) were the coldest of the AIM record”–that is, since 2007 when NASA’s AIM spacecraft began monitoring noctilucent clouds.

Last summer, NLCs spread as far south as Los Angeles and Las Vegas, setting records for low-latitude sightings. The growing chill today suggests this summer could be just as good–or maybe even better. In fact, the first sightings in the continental USA (Washington and Minnesota) have already happened.

Observing tips: The best time to look is during the hours after sunset (or before sunrise) when the sun is more than 6 degrees below the horizon: diagram. If you see electric-blue tendrils spreading across the sky, you may have spotted a noctilucent cloud.

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Inferior Conjunction of Venus

June 2, 2020: Tomorrow, June 3rd, Venus will pass almost directly between the Earth and the sun. This is having a strange effect on the planet’s shape. “It is like a ring of fire,” says Didier Favre, who sends this picture from Brétigny-sur-Orge, France:

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When Favre took the picture on June 1st, the sun was only 2 degrees from Venus–hence the blue sky. “It was not an easy picture to take,” says Favre, “but what a beautiful view!”

Why does Venus look like a ring? Simple: The planet’s nightside is facing Earth. Sunlight filtering through the edge of Venus’s carbon dioxide atmosphere forms a luminous ring around the dark disk.

Astronomers call this an “inferior conjunction of Venus,” and it’s one of the best in decades. At closest approach on June 3rd, Venus will be only 29 arcminutes (about half a degree) from the center of the solar disk. Only twice since 1961 has Venus come closer–during the famous Venus Transits of 2004 and 2012 [ref].

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A SOHO coronagraph image of the ongoing conjunction. The horizontal line running through Venus is caused by the planet’s bright light overloading the pixels of SOHO’s digital camera.

Observing Venus at this time is dangerous. With the sun just a fraction of a degree away, it is easy for stray sunlight to sneak into optical systems, damaging sensitive electronics and hurting human eyes. Only skilled observers taking careful precautions should attempt it.

In space, the Solar and Heliospheric Observatory (SOHO) will be monitoring the conjunction. Coronagraphs onboard SOHO use opaque disks to block the glare of the sun, revealing nearby stars and planets.  It’s a type of  artificial solar eclipse.

Even SOHO will have some trouble, though. On June 3rd, Venus will be so close to the sun that it briefly dips behind the coronagraph’s opaque disks, hiding the moment of closest approach. Ground-based observers will have to try to fill in the gap.

Browse the Realtime Venus Photo Gallery for the latest images.

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Introducing, the Green Ghost

May 31, 2020: Want to discover something new? Keep an eye on the tops of thunderstorms. Sprites, trolls, elves and pixies: These are just a handful of the exotic phenomena that have surprised researchers monitoring cloudtops since the 1980s. In fact, a new one has just been discovered. Introducing, the Green Ghost.

Thomas Ashcraft captured one over New Mexico on May 25th. Play his movie, and look for the green afterglow following the flash of this magnificent jellyfish sprite:

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“In the past week I’ve captured two Green Ghosts over west Texas that were generated by strong peak current lightning strokes,” says Ashcraft. “The one on May 25th registered  118 kAmperes on the National Lightning Detection Network and saturated VLF lightning sensors as far away as great Britain and Germany.”

“As far as I know there are no scientific journal articles regarding this new phenomenon and a handful of citizen scientists are leading the way,” says Ashcraft.

Green Ghosts were discovered only 1 year ago by Hank Schyma, a Houston Texas-based storm chaser better known to his fans as Pecos Hank. “It was May 25, 2019,” recalls Schyma. “I video recorded some sprites over a storm in Oklahoma. Later, when I reviewed the footage, I noticed a mysterious green afterglow above some of the larger sprites.”

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Above: From the archives of Thomas Ashcraft, a Green Ghost photographed in 2014. “At the time I did not realize what I had captured,” he says.

Schyma worked closely with another storm chaser, Paul M. Smith. “We shared the footage with scientists and others on social media. Nobody had heard of it before. Many argued it might be a camera sensor artifact. Over the following weeks and months, Paul captured multiple other ghosts at high resolution, silencing the skepticism.”

At the moment, no one knows for sure what causes Green Ghosts. Their color may be a clue. Green is commonly seen in auroras and airglow, two upper atmospheric phenomena that get their verdant hue from excited atoms of oxygen. The same could hold true for Green Ghosts. When the tops of strong sprites hit the airglow layer ~90 km above Earth’s surface, oxygen atoms might briefly glow green.

Right or wrong, this hypothesis inspired the name Ghost. “It is an acronym for Green emissions from excited Oxygen in Sprite Tops,” explains Schyma. “More importantly, we named them ghosts to maintain the theme of other transient luminous events such as sprites, trolls, elves and pixies.”

In the USA, sprite season is just getting underway as summer approaches, bringing severe electrical storms. Stay tuned for more ghost stories.

 

Noctilucent Clouds are Intensifying

May 28, 2020: On May 17th, NASA’s AIM spacecraft detected the first noctilucent clouds (NLCs) of summer. Those first electric-blue smudges were barely visible. Since then, however, the clouds have rapidly intensified. Recent images from orbit show a growing bank of NLCs pinwheeling just inside the Arctic Circle:

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NLCs are Earth’s highest clouds. Seeded by meteoroids, they float at the edge of space more than 80 km above the ground. The clouds form when summertime wisps of water vapor rise up to the mesosphere, allowing water to crystallize around specks of meteor smoke. Last summer, they spread as far south as Los Angeles and Las Vegas, setting records for low-latitude sightings.

It’s early in the 2020 season, so the clouds are still concentrated around the North Pole. Nevertheless, people in Europe are starting to see them. Johny Krahbichler sends this picture taken last night (May 26th) from Ängelholm, Sweden:

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“These night glowing clouds are pretty common during the summer here in Sweden,” says Krahbichler. “But it’s rare that they glow this brightly over such a large area. As soon as I saw them I ran to get my camera. The glow from the clouds ended up matching the glow of my LED strip inside!”

Noctilucent clouds have been likened to a great “geophysical light bulb” because they turn on abruptly, reaching almost full intensity over a period of ~10 days. By early June, therefore, we can expect the clouds to spread farther south with a significant increase in brightness. The circular rhythm of the pinwheel motion (caused by a 5-day planetary wave) may even allow us to start issuing predictions of latitude ranges where the clouds are most likely to appear.

Stay tuned for updates–and be alert for electric blue.

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