May 27, 2021: Something unusual is happening at the top of Earth’s atmosphere. Noctilucent clouds (NLCs) are forming, and people are seeing them from the ground even though it is only May. Andy Stables sends this photo from the Isle of Skye, Scotland, taken May 26th:
The electric-blue ripples “were clearly visible to the unaided eye,” says Stables. “This is the earliest I have ever seen them here in Scotland.”
NLCs are Earth’s highest clouds. Seeded by meteoroids, they float at the edge of space about 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. The season for bright naked-eye NLCs typically stretches from June through August.
This year NLCs are getting an early start. We’ve already received multiple reports of sightings in Europe from latitudes as low as 50 degrees, and according to NASA’s AIM spacecraft the clouds are rapidly intensifying. In only 4 days since the clouds were first spotted, their coverage of the Arctic has multiplied 10-fold:
The reason may be extra water in the mesosphere: NASA satellite data show that 2021 is one of the wettest years since 2007. NLCs have more H2O to work with–hence the early start and rapid growth.
In recent years, summertime noctilucent clouds have spilled as far south as Los Angeles and Las Vegas, setting records for low-latitude sightings. 2021 is shaping up to be such a year. Pro tip for northern sky watchers: Look west 30+ minutes after sunset. If you see luminous blue-white tendrils spreading across the sky, you may have spotted a noctilucent cloud
May 22, 2021: The 2021 season for noctilucent clouds (NLCs) is underway. NASA’s AIM spacecraft detected the first electric-blue NLCs over Ellesmere Island in northern Canada on May 20th:
NLCs are Earth’s highest clouds. Seeded by meteoroids, they float at the edge of space about 83 km above the ground. The clouds form around Earth’s poles when summertime wisps of water vapor rise up to the mesosphere, allowing water to crystallize around specks of meteor smoke. In recent years they have spread as far south as Los Angeles and Las Vegas, setting records for low-latitude sightings.
This year the mesosphere is unusually wet. “2021 is one of the wettest years in the AIM record,” says Lynn Harvey of the University of Colorado’s Laboratory for Atmospheric and Space Physics, who processed data from NASA’s Microwave Limb Sounder (MLS) to check conditions in the noctilucent zone. Click here to see her results. Only once or twice in the past 14 years have NLCs had more water to work with.
The extra water bodes well for a strong season. In fact, there have already been ground sightings. “We saw the first NLC from Germany on May 21st,” reports Gerd Baumgarten of the Leibniz-Institute of Atmospheric Physics. “The clouds appeared in the feed from one of our high resolution cameras located in Collm (51.3N, 13.0E).”
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“The display was quite faint,” he notes. They may not remain faint for long, however. Previous data from AIM show that NLCs are like a great “geophysical light bulb.” They turn on every year in late spring, reaching almost full intensity over a period of no more than 10 days.
Observing tips: Look west 30 to 60 minutes after sunset. If you see luminous blue-white tendrils spreading across the sky, you may have spotted a noctilucent cloud. Early season NLCs are typically confined to high latitudes, spreading south as northern summer unfolds.
May 15, 2021: You know a solar storm is serious when buildings burst into flame. Sounds crazy? It really happened 100 years ago today.
On May 15, 1921, the biggest solar storm of the 20th century hit Earth. Around 02:00 GMT that Sunday morning a telegraph exchange in Sweden burst into flames. Across the Atlantic, the same thing was going on in 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. During the conflagration, long distance telephone lines burned out in New Brunswick; voltages on telegraph lines in the USA spiked as high as 1000 V; and auroras were sighted by ships at sea crossing the equator. It was a Big. Solar. Storm.
The outburst happened during the lazy tail end of Solar Cycle 15, an unremarkable cycle that was almost over in 1921. Sunspot numbers were low–but it only took one. Giant sunspot AR1842 appeared in mid-May and started flaring, hurling multiple coronal mass ejections (CMEs) toward Earth. In those days scientists had never heard of “CMEs,” so they were completely surprised when the clouds of plasma struck Earth. Around the world, magnetometers suddenly went offscale, pens in strip chart recorders pegged uselessly to the tops of their papers.
In response to the pummeling, Earth’s magnetic field swayed back and forth, rippling with energy. Fires were a direct result. Physics 101: When a magnetic field changes rapidly, electricity flows through conductors in the area. It’s called “magnetic induction.” Early 20th century telegraph lines suddenly found themselves buzzing with induced currents. In Sweden and New York, wires grew so hot they ignited telegraph papers and other combustibles.
What would happen if the same storm struck today? A 2013 Royal Academy of Engineering report summarizes the possibilities. Suffice it to say, fire would be the least of our worries. Modern technology is far more sensitive to solar activity than the simple copper wires of 1921. The same solar storm today could black out regional power grids, expose air travelers to radiation, knock out satellites, and disable radio-based technologies such as GPS.
Loss of electricity is often cited as the worst likely side-effect of a solar superstorm, but power systems are more resilient than they used to be. Thanks to improvements made after the Great Quebec Blackout of 1989, many modern grids would bounce back quickly. A more worrisome loss might be GPS. We think of GPS as our main way of finding things: ambulances finding accidents, pilots finding runways, and so on. But there’s more to it than that. GPS tells us what time it is, a service of atomic clocks onboard the satellites. In fact, GPS time is woven into the fabric of modern society.
“Telecom networks rely on GPS clocks to keep cell towers synchronized so calls can be passed between them. Many electrical power grids use the clocks in equipment that fine-tunes current flow in overloaded networks. The finance sector uses GPS-derived timing systems to timestamp ATM, credit card, and high-speed market transactions. Computer network synchronization, digital television and radio, Doppler radar weather reporting, seismic monitoring, even multi-camera sequencing for film production—GPS clocks have a hand in all.”
“What if all these flying clock radios were wiped out, and everything on the ground started blinking 12:00?” asks the author, Dan Glass. Answer: “Nobody knows.”
Space weather scholars routinely call the May 1921 event a “100 year storm.” However, recent research (both historical and statistical) suggests that such storms come along more often–every 40 to 60 years. Either way, we’re overdue.
May 9, 2021: The biggest comet in the Solar System is actually a planet. It’s Mercury. Researchers have known for years that Mercury has an enormous tail. Last week, Andrea Alessandrini photographed it from the balcony of his house in Veroli, Italy:
“I took the picture on May 5th using a 66 mm (2.5 inch) refracting telescope and a Pentax K3-II camera,” says Alessandrini, an amateur astronomer who works by day as an aerospace engineer. “This is a 7 minute exposure @ ISO 1000.”
First predicted in the 1980s, Mercury’s tail was discovered in 2001. Its source is Mercury’s super-thin atmosphere. Mercury is so close to the sun, pressure from sunlight itself can push atoms out of the atmosphere and into space. The escaping gas forms a tail more than 24 million km long.
The key to detecting Mercury’s tail is sodium. There are many elements in Mercury’s tail; sodium is only one. But because sodium is so good at scattering yellow light, it is the best element for tracing the long plume of gas. “I use a special 589 nm filter tuned to the yellow glow of sodium,” says Alessandrini. “Without that filter, Mercury’s tail would be invisible.”
NASA’s MESSENGER spacecraft spent years observing Mercury’s tail often from close range. This movie shows how the brightness of the tail varies as Mercury orbits the sun:
For reasons having to do with the Doppler shift of sodium absorption lines in the solar spectrum, Mercury’s tail is brightest when the planet is ±16 days from perihelion (closest approach to the sun). Read the research here.
That special date is this week: On May 13th, Mercury will be 16 days past perihelion and the tail could be as much as 10 times brighter than Alessandrini saw last week. Coincidentally, on that same day the crescent Moon will pass by Mercury in the evening sky. Can you say “photo-op”? Just don’t forget your sodium filter…. [sky map]
May 6, 2021: China’s new space station is just getting started, but it’s already putting on a good show. “I’ve seen it twice this week,” reports Mark A. Brown of Marion, Iowa. “The space station’s Tianhe-1 module has been making brilliant passes across Middle America.” Here it is rivaling the star Vega on May 4th:
“In the photo, I also caught the tumbling Long March 5B booster, which helped loft the module into orbit,” says Brown. “The booster flares brilliantly (visual magnitude -1) in reflected sunlight as it tumbles along Tianhe-1’s path. Both objects are easily seen with the naked eye.”
China launched the Tianhe-1 module on April 29th. It is the first of three modules that will eventually join to create the Chinese Space Station (CSS). When the CSS is finished, it will be about as big as Russia’s old Mir space station, roughly a quarter of the mass of the ISS. Three astronauts will live onboard.
On May 5th, Tianhe-1 flew over Manorville, New York, where Philip Smith photographed it through a 14-inch telescope:
“I was lucky to get this image,” says Smith. “The module was already 56 degrees above the horizon when it popped out of Earth’s shadow–so I didn’t have much time. Less than a minute later it was at its maximum altitude of 76 degrees, and that’s when I caught it.”
Readers, you can see the new space station with your own eyes. Visit Heavens-Above.com and select flyby predictions for Tianhe-1. Many towns and cities in the USA have a good view this week. Pro tip: Go outside at least 10 minutes early; you might see the tumbling booster rocket, too.
EXTRA: The Long March 5B booster rocket is out of control. Forecasters expect it to re-enter Earth’s atmosphere on May 8th or 9th, with pieces landing … no one knows where. There is a 70% chance of an ocean splashdown, and experts say human injuries are unlikely.
Spaceweather.com 
