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:

“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.

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.

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.”

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.

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.

 

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:

“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.

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:

“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!

Realtime Noctilucent Cloud Photo Gallery
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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:

“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.

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.

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:

“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.

“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.

Realtime Noctilucent Cloud Photo Gallery
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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:

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].

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.

Realtime Venus Photo Gallery
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