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:


“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.


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:


“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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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:


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].


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:


“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.”


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:


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:


“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.

Realtime Noctilucent Cloud Photo Gallery
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Is the South Atlantic Anomaly Splitting in Two?

May 26, 2020: New data from Europe’s Swarm satellites show something strange is afoot in Earth’s magnetic field. The South Atlantic Anomaly might be splitting in two. “A new, eastern minimum of the South Atlantic Anomaly has appeared over the last decade,” says Jürgen Matzka, from the German Research Center for Geosciences. “In recent years it has been developing vigorously.”


Above: Development of the South Atlantic Anomaly from 2014 to 2020. Credit: ESA/Swarm. [more]

The South Atlantic Anomaly is a weak spot in Earth’s magnetic field centered roughly on the Atlantic side of South America. Discovered in 1958, it has been growing and shifting for decades. The latest data from Swarm show a new weak spot forming just off the southern tip of Africa.

“We are very lucky to have the Swarm satellites in orbit to investigate this development,” says Matzka.

Launched in November 2013, Swarm is a constellation of 3 identical satellites flying in formation around Earth. They are equipped with magnetometers, star trackers and other instruments, which allow the satellites to make exquisitely detailed 3D measurements of Earth’s magnetic field. The possible splitting of the Anomaly is just one of the mission’s many significant findings.

Researchers have long known that Earth’s magnetic field is weakening. Over the last 200 years, the globally averaged magnetic field has lost around 9% of its strength, with the South Atlantic Anomaly leading the way. From 1970 to 2020, the minimum field strength in this area dropped from 24,000 nanoteslas to 22,000.


Above: Radiation strikes detected by Swarm are concentrated in the South Atlantic Anomaly. Credit: ESA

As the South Atlantic Anomaly has weakened, the inner Van Allen Belt has spilled into it, allowing energetic particles (especially protons) to get within 200 km of Earth’s surface. This poses little threat to people on the ground, but spacecraft  aren’t so lucky. When satellites fly through the Anomaly, they are exposed to relatively strong radiation. Onboard computers may reboot and digital cameras can be fogged by streaks of charged particles flying through them. The ISS has extra shielding to deal with this problem, and the Hubble Space Telescope doesn’t even bother to make observations when it is inside the Anomaly.

If the South Atlantic Anomaly eventually splits into two cells, satellite mission planners will have to contend with a new zone of high radiation. The splitting is more than just a nuisance, however. It could offer clues to the origin of the Anomaly itself.  Earth’s magnetic field is created by currents of superheated liquid iron swirling ~3000 km beneath our feet. Changes “up here” can tell researchers what’s going on “down there.”

Stay tuned for updates as the Swarm mission continues.

Noctilucent Cloud Season Has Begun

May 20, 2020: NASA’s AIM spacecraft has detected a noctilucent cloud (NLC) inside the Arctic Circle–the first of the 2020 summer season. It is the blue puff in this satellite image of the North Pole:

The detection on May 17th marks one of the earliest starts in the 14 year history of the spacecraft. “In previous years, we have seen the first NLCs appear between May 15th and May 27th,” says Cora Randall, a member of the AIM science team at the University of Colorado. “Only once, in 2013 (May 15th), has the northern season started earlier than this.”

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.

To find out why NLCs appeared so early this year, Lynn Harvey of the University of Colorado’s Laboratory for Atmospheric and Space Physics looked at data from NASA’s Microwave Limb Sounder (MLS). The following plots show moisture and temperature in the mesosphere for the past 14 years, with 2020 traced in red:

“Between May 1st and May 17th, conditions in the mesosphere significantly cooled and moistened,” says Harvey, “such that 2020 became the second coldest and third wettest year in the AIM record.”

Noctilucent clouds have been likened to a great “geophysical light bulb” because they turn on abruptly, reaching almost full intensity over a period of no more than 5 to 10 days. This means the little blue puff could soon expand to cover most of the Arctic. Stay tuned!

Red and Green Ripples in the Sky

May 15, 2020: This week, an astronomer at the McDonald Observatory discovered a planet with fantastic red and green ripples in its atmosphere. It looks a lot like Texas.

On May 13th, around 10:30 pm, Stephen Hummel was walking across the observatory grounds when he noticed the flash of lightning from a distant thunderstorm. “I saw a large column of sprites and rushed to set up my camera on a ridge with a better view,” he says. “Aiming southeast towards the city of Alpine, Texas, I recorded this movie.”

Hummel’s movie is rare and beautiful. It shows alternating bands of red and green airglow gliding overhead like ripples in a giant pool of water, punctuated by red bolts of upward directed lightning. The flickering sprites were so bright, he could see them with his unaided eye.

“In a hurry not to miss any action, I hiked quickly up the ridge with my camera,” he recalls. “Out of breath, I heard the eerie but distinct sound of a mountain lion’s call. I left the camera running while I returned to the safety indoors, then gathered the footage later on, hoping for the best. I was amazed by the results and surprised the airglow was so evident.”

Both the sprites and the airglow-ripples came from a thunderstorm about 180 miles away. This weather radar map shows Hummel’s location (starred) and the instigating storm system:


This was a convective storm with powerful updrafts. Essentially, the storm pounded the upper atmosphere from below, creating a bulls-eye pattern in the mesosphere more than 80 km above the ground. This pattern impressed itself upon the airglow layer, exciting and amplifying aurora-like colors which are usually too faint to see.

It’s no coincidence that Hummel saw sprites at the same time. Powerful convective storms produce strong lightning–both up and down. Hummel witnessed not only the bright glow of ordinary lightning bolts lancing down to Earth, but also the eerie forms of sprites reaching up to the edge of space. “The sprites were easily visible to the unaided eye,” he says.

“Thanks to the mountain lion,” he adds, “I recorded the whole thing.”

The Great Geomagnetic Storm of May 1921

May 12, 2020: 99 years ago this week, people around the world woke up to some unusual headlines.

“Telegraph Service Prostrated, Comet Not to Blame” — declared the Los Angeles Times on May 15, 1921. “Electrical Disturbance is ‘Worst Ever Known'” — reported the Chicago Daily Tribune. “Sunspot credited with Rail Tie-up” — deadpanned the New York Times.


They didn’t know it at the time, but those newspapers were covering the biggest solar storm of the 20th Century. Nothing quite like it has happened since.

It began on May 12, 1921 when giant sunspot AR1842, crossing the sun during the declining phase of Solar Cycle 15, began to flare. One explosion after another hurled coronal mass ejections (CMEs) directly toward Earth. For the next 3 days, CMEs rocked Earth’s magnetic field. Scientists around the world were surprised when their magnetometers suddenly went offscale, pens in strip chart recorders pegged uselessly to the top of the paper.

And then the fires began. Around 02:00 GMT on May 15th, a telegraph exchange in Sweden burst into flames. About an hour later, the same thing happened across the Atlantic in the village of Brewster, New York. Flames engulfed the switch-board at the Brewster station of the Central New England Railroad and quickly spread to destroy the whole building. That fire, along with another one about the same time in a railroad control tower near New York City’s Grand Central Station, is why the event is sometimes referred to as the “New York Railroad Superstorm.”


A photograph (Royal Greenwich Observatory) and sketch (Mount Wilson Observatory) of sunspot AR1842 on May 13, 1921. Source: “The extreme solar storm of May 1921: observations and a complextopological model

What caused the fires? Electrical currents induced by geomagnetic activity surged through telephone and telegraph lines, heating them to the point of combustion. Strong currents disrupted telegraph systems in Australia, Brazil, Denmark, France, Japan, New Zealand, Norway, Sweden, the UK and USA. The Ottawa Journal reported that many long-distance telephone lines in New Brunswick were burned out by the storm. On some telegraph lines in the USA voltages spiked as high as 1000 V.

During the storm’s peak on May 15th, southern cities like Los Angeles and Atlanta felt like Fairbanks, with Northern Lights dancing overhead while telegraph lines crackled with geomagnetic currents. Auroras were seen in the USA as far south as Texas while, in the Pacific, red auroras were sighted from Samoa and Tonga and ships at sea crossing the equator.

What would happen if such a storm occurred today?

Researchers have long grappled with that question–most recently in a pair of in-depth papers published in the journal Space Weather: “The Great Storm of May 1921: An Exemplar of a Dangerous Space Weather Event” by Mike Hapgood (Rutherford Appleton Laboratory, UK) and “Intensity and Impact of the New York Railroad Superstorm of May 1921” by Jeffrey Love (US Geological Survey) and colleagues.

The summary, above, is largely a result of Hapgood’s work. He painstakingly searched historical records including scientific journals, newspaper clippings, and other reports to create a moment-by-moment timeline of the storm. Such timelines are invaluable to emergency planners, who can use them to prepare for future storms.


Locations where auroras were sighted in May 1921. The leftmost red circle marks Apia, Samoa.

Jeffrey Love and colleagues also looked into the past and–jackpot!–they found some old magnetic chart recordings that did not go offscale when the May 1921 CMEs hit. Using the data, they calculated “Dst” (disturbance storm time index), a measure of geomagnetic activity favored by many space weather researchers.

“The storm attained an estimated maximum −Dst on 15 May of 907 ± 132 nT, an intensity comparable to that of the Carrington Event of 1859,” they wrote in their paper.

This dry-sounding result upends conventional wisdom. Students of space weather have long been taught that the Carrington Event (-Dst = 900 nT) was the strongest solar storm in recorded history. Now we know that the May 1921 storm was about equally intense.

If the May 1921 storm hit today, “I’d expect it to lead to most, if not all, of the impacts outlined in the 2013 Royal Academy of Engineering report led by Paul Cannon,” says Hapgood. “This could include regional power outages, profound changes to satellite orbits, and loss of radio-based technologies such as GPS. The disruption of GPS could significantly impact logistics and emergency services.”

It’s something to think about on the 99th anniversary of a 100-year storm….

Hyperbolic Comet SWAN

April 19, 2020:  Newly-discovered Comet SWAN (C/2020 F8) is shaping up to be a beauty. It looks great through small telescopes now, and could become visible to the naked eye next month. Gerald Rhemann sends this picture taken yesterday from Farm Tivoli, Namibia:

“The comet’s tail is almost a full degree long,” says Rhemann. “And it was an easy target for my 12-inch telescope at magnitude +7.5.”

Where does this beautiful comet come from? SWAN’s trajectory is an important clue. It’s falling toward the sun for the first time, and the sun’s gravity will probably slingshot Comet SWAN back into deep space. Comet SWAN may be a “hyperbolic comet“–that is, a comet whose orbit has an eccentricity greater than 1. Such comets come from the Oort Cloud or may even be interstellar.

The case for Comet SWAN being a hyperbolic comet is not ironclad. Based on an observation arc of only 3 days, JPL reports the eccentricity of SWAN’s orbit as 1.1 +/- 0.2.  The error bars are still large. The uncertainties will shrink, however, as more observations are added to the database in the nights ahead. Stay tuned for updates.

UPDATE (May 6, 2020): JPL has updated the comet’s eccentricity to 1.00095608 +/- 0.0011254 based on 18 days of data. It is definitely hyperbolic.