Neutrons Detected on Commercial Airplane Flights

March 13, 2019: Long lines. Narrow seats. Baggage fees. You recognize this list. It’s the downside of flying on modern commercial airlines. And now we have a new item to add: cosmic ray neutrons.

Spaceweather.com and Earth to Sky Calculus have just completed a 5-continent survey of neutron radiation at aviation altitudes. From December 2018 through February 2019, Hervey Allen of the University of Oregon’s Network Startup Resource Center carried  Earth to Sky radiation sensorsincluding neutron bubble chambers–onboard commercial flights from North America to Europe, Africa, South America and Asia.

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Hervey logged 83 hours in the air as he traveled 41,500 miles above 30,000 feet. For reference, that’s almost twice the circumference of the Earth. The entire time, he gathered data on X-rays, gamma-rays and neutrons in an energy range (10 keV to 20 MeV) similar to that of medical radiology devices and “killer electrons” from the Van Allen Radiation Belts.

The results were eye-opening. During the trip, Hervey recorded 230 uGy (microGrays) of cosmic radiation. That’s about the same as 23 panoramic dental x-rays or two and a half chest X-rays. Moreover, 41% of the dose came in the form of neutrons. This confirms that cosmic-ray neutrons are abundant at aviation altitudes and must be considered in any discussion of “Rads on a Plane.”

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Each bubble represents a cosmic ray neutron penetrating the chamber. Left: Neutrons on board a flight from San Francisco to South Korea. Right: Neutrons detected while crossing the Atlantic Ocean from New Jersey to Brussels.

Researchers have long known that cosmic rays penetrate airplanes. Our own 3-year survey of global radiation shows that X-rays and gamma-rays at aviation altitudes are typically 50 times stronger than sea level. This new survey focuses on neutrons, a more potent type of radiation from deep space. Studies show that neutrons can be ten times more effective at causing biological damage compared to X-rays and gamma-rays in the same energy range. Neutrons are so effective, they are used for cancer therapy, killing tumors better than other forms of radiation.

Should we be worried about Hervey? Although he absorbed a lot of radiation during the survey, he did so slowly. Hervey’s whole body dose was spread out over 14 flights and 3 months–unlike, say, a dental X-ray which is localized to the jaw and delivered in a split-second. Slow delivery gives the body time to respond, repair damage, and move on without obvious health effects. On the other hand, at least one study shows that low-dose radiation received over a long period of time may slightly increase the risk of leukaemia, while flight attendants have been found to have a higher risk of cancer than the general population.

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Left: Neutrons detected while flying from Europe to Accra, Ghana. Right: Ground-level measurements in Ghana with giant ant mounds in the background.

Our survey also revealed some geographical variations. Generally speaking, neutron radiation was stronger near the Arctic Circle and weaker near the equator. It was weakest of all, however, in flights over Chile as the aircraft skirted the South Atlantic Anomaly. We will be investigating these variations with additional flights in the near future.

Stay tuned!

The CMEs Are Coming. (Maybe)

March 9, 2019: Earth is about to be sideswiped by a pair of coronal mass ejections (CMEs). Maybe. The two solar storm clouds left the sun on March 8th when sunspot AR2734 erupted, producing a C1-class solar flare. NASA’s Solar Dynamics Observatory recorded the blast:


Above: This movie comes from SDO’s extreme ultraviolet telescope–hence the strangely beautiful colors.

The explosion and its ultraviolet afterglow lasted for more than an hour. Such long-duration flares are notorious for producing “solar tsunamis” and CMEs. Indeed, in the global movie, below, a shadowy shockwave may be seen billowing away from the blast site like a ripple in a giant pond. That wave hurled two faint coronal mass ejections (CMEs) into space.

NOAA analysts have modeled the eruption and reached the following conclusions: On March 11th, one CME will pass just behind Earth while the other passes just in front. Both could deliver glancing blows to our planet’s magnetic field. Minor G1-class geomagnetic storms are possible when Earth splits the gap between these two solar storm clouds.

In recent months, geomagnetic storms have been caused mainly by streams of solar wind flowing from holes in the sun’s atmosphere. CMEs tend to be more effective instigators of geomagnetic storms and auroras. This is because of intense shocks and strong magnetic fields CMEs often contain.

There’s no guarantee these CMEs will hit Earth. Just in case, Arctic sky watchers should be alert for bright lights on Monday night. Subscribers to our Space Weather Alert service will receive an instant text message when the CMEs arrive. Aurora Alerts: SMS text, email.

A Really Weird Solar Eclipse

March 7, 2019: Earlier today, NASA’s Solar Dynamics Observatory (SDO) observed an eclipse of the sun–a strange kind of eclipse that you can only see while orbiting Earth. The black disk of the New Moon passed in front of the sun, reversed course, and did it again:

During the eclipse, which lasted just over 4 hours, as much as 82% of the sun was covered. Technically, that makes it an annular solar eclipse, not total. At maximum, an annulus or “ring of fire” completely surrounded the Moon.

The strange “double-dip” motion of the Moon across the sun is a result of orbital mechanics. Both SDO and the Moon are orbiting Earth, but at different speeds. SDO’s velocity of ~3 km/s is faster than the Moon’s velocity of 1 km/s. SDO thus overtakes the Moon first in one direction, then the other, during the long eclipse.

High-resolution images of the eclipse reveal that the Moon is not perfectly smooth. The little bumps and irregularities you see are lunar mountains backlit by solar plasma:

Images like these have practical value to the SDO science team. The sharp edge of the lunar disk helps researchers measure the in-orbit characteristics of the telescope–e.g., how light diffracts around the telescope’s optics and filter support grids. Once these are calibrated, it is possible to correct SDO data for instrumental effects and sharpen images of the sun even more than before.

Realtime Space Weather Photo Gallery

A Month Without Sunspots

March 1, 2019: There are 28 days in February. This year, all 28 of them were spotless. The sun had no sunspots for the entire month of Feb. 2019. This is how the solar disk looked every day:

The last time a full calendar month passed without a sunspot was August 2008. At the time, the sun was in the deepest Solar Minimum of the Space Age. Now a new Solar Minimum is in progress and it is shaping up to be similarly deep. So far this year, the sun has been blank 73% of the time–the same as 2008.

Solar Minimum is a normal part of the solar cycle. Every ~11 years, sunspot counts drop toward zero. Dark cores that produce solar flares and CMEs vanish from the solar disk, leaving the sun blank for long stretches of time. These minima have been coming and going with regularity since the sunspot cycle was discovered in 1859.

However, not all Solar Minima are alike. The last one in 2008-2009 surprised observers with its depth and side-effects. Sunspot counts dropped to a 100-year low; the sun dimmed by 0.1%; Earth’s upper atmosphere collapsed, allowing space junk to accumulate; the pressure of the solar wind flagged while cosmic rays (normally repelled by solar wind) surged to Space Age highs. All these things are happening again.

How does this affect us on Earth? The biggest change may be cosmic rays. High energy particles from deep space penetrate the inner solar system with greater ease during periods of low solar activity. Indeed, NASA spacecraft and space weather balloons are detecting just such an increase in radiation. Cosmic rays can alter the flow of electricity through Earth’s atmosphere, trigger lightning, potentially alter cloud cover, and dose commercial air travelers with extra “rads on a plane.”

As February ended, March is beginning … with no sunspots. Welcome to Solar Minimum!

What Kind of Sunspot is That?

March 5, 2019: Today, a tiny sunspot is struggling to form in the sun’s northern hemisphere. It is so small, it has not yet been numbered, and it may fade away before the day is done, leaving the sunspot number technically zero. Even if it vanishes, though, this funny little sunspot is worth mentioning because of its tilted magnetic field:

This is a magnetogram (magnetic map) of the sun obtained on March 5th by NASA’s Solar Dynamics Observatory. The sunspot is inset. Note how its magnetic field is almost orthogonal to other patches of magnetism elsewhere on the solar disk.

Sunspots are islands of magnetism floating on the surface of the sun. Like all magnets, they have two poles, plus (+) and minus (-). Usually these poles are aligned almost parallel to the sun’s equator. Today’s sunspot is almost perpendicular.

Could this be a sunspot from the next solar cycle? Right now, Solar Cycle 24 is decaying into a deep Solar Minimum. Solar Cycle 25 is still in the offing. According to Hale’s Law, sunspot magnetic fields reverse polarity between solar cycles. If this sunspot continues to grow–and if its magnetic axis tilts a bit to the right–Hale’s Law would tag it as a member of Solar Cycle 25.

Postscript: The sunspot did continue to grow, and its magnetic field remained ambiguous. Based on its relatively low latitude, we believe it is probably a member of old Solar Cycle 24.

Physics of An Exploding Cosmic Ray Balloon

Feb. 21, 2019: On Nov. 14, 2018, the students of Earth to Sky Calculus launched a space weather balloon to measure increasing levels of cosmic rays in the atmosphere. At the apex of the flight, the balloon exploded and the radiation sensors parachuted back to Earth. A video camera on top of the payload recorded the pop:

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These images illustrate recent findings about the physics of exploding balloons. In a Physical Review Letter entitled “Popping Balloons: A Case Study of Dynamical Fragmentation,” researchers from the Ecole Normale Supérieure in Paris report a series of laboratory experiments in which one balloon after another was popped and analyzed.

Basically, there are two ways a balloon can pop: along a single tear (the “opening regime”) or along many tears (the “fragmentation regime”). This video shows the two regimes in action. Which way the balloon decided to pop depends on the stress in the rubber membrane. When the stress is low, it can be relieved with a single tear, but when the stress is high, many tears are required to do the job.

Space weather balloons explode in the fragmentation regime, and the new research explains why. When space weather balloons are launched, they measure no more than 6 to 8 feet in diameter. By the time they reach the stratosphere, they have stretched into a sphere as wide as a house. So much stress requires many tears to release.

More information about this research is available from the American Physical Society.

Cosmic Rays Increasing for the 4th Year in a Row

Feb. 21, 2019: Cosmic rays in the stratosphere are intensifying for the 4th year in a row. This finding comes from a campaign of almost weekly high-altitude balloon launches conducted by the students of Earth to Sky Calculus. Since March 2015, there has been a ~13% increase in X-rays and gamma-rays over central California, where the students have launched hundreds of balloons.

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The grey points in the graph are Earth to Sky balloon data. Overlaid on that time series is a record of neutron monitor data from the Sodankyla Geophysical Observatory in Oulu, Finland. The correlation between the two data sets is impressive, especially considering their wide geographic separation and differing methodologies. Neutron monitors have long been considered a “gold standard” for monitoring cosmic rays on Earth. This shows that our student-built balloons are gathering data of similar quality.

Why are cosmic rays increasing? The short answer is “Solar Minimum.” Right now, the 11-year solar cycle is plunging into one of the deepest minima of the Space Age. The sun’s weakening magnetic field and flagging solar wind are not protecting us as usual from deep-space radiation. Earth to Sky balloon launches in multiple countries and US states show that this is a widespread phenomenon.

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Cosmic rays are of interest to anyone who flies on airplanes. The International Commission on Radiological Protection has classified pilots as occupational radiation workers because of cosmic ray doses they receive while flying. A recent study by researchers at the Harvard School of Public Health shows that flight attendants face an elevated risk of cancer compared to members of the general population. They listed cosmic rays as one of several risk factors. There are also controversial studies that suggest cosmic rays promote the formation of clouds in the atmosphere; if so, increasing cosmic rays could affect weather and climate.

Asteroid to Eclipse Sirius

Feb. 17, 2019: On Monday night, Feb. 18th, the brightest star in the night sky will disappear. It’s a rare eclipse of Sirius by asteroid 4388 Jürgenstock. As recently as two days ago, specialists thought the eclipse would be visible in a narrow corridor cutting across the central USA. New calculations, however, suggest a different path:

Sirius’s shadow will cross southern parts of Chile and Argentina, Central America and the Caribbean. This will happen on Feb. 18th between 09:11 pm PST and 09:27 pm PST.

According to David Dunham of the International Occultation Timing Association, the eclipse could last for as much as 1.8 seconds, with Sirius fading to minimum brightness for 0.2 seconds of that time. The angular diameter of Sirius is 0.006 arcseconds. Asteroid Jürgenstock is just a little wider: 0.007 arcseconds, so theoretically Sirius should be completely blocked. “But the asteroid may be a little larger or smaller than predicted, and it’s likely to be irregularly-shaped, so there is a good chance that even at the center, the star will not completely disappear,” notes Dunham.

Named after Venezuelan astrometrist Jürgen Stock, asteroid 4388 Jürgenstock orbits the sun in the inner regions of the asteroid belt between Mars and Jupiter. It is approximately 5 kilometers (3.1 miles) in diameter. Video recordings of the eclipse could help trace the shape of the distant space rock.

Resources: finder charts, observing tips, eclipse home page.

A Meteoroid Hits the Moon During Lunar Eclipse

Jan. 22, 2019: On Jan. 21st at 04:41:43 UT, a meteoroid slammed into the Moon. We know this because so many people witnessed the explosion. It happened during a total eclipse of the Moon, visible from five continents. Dr. Fritz Helmut Hemmerich photographed the eclipse from the Canary Islands of Spain and captured the fireball:

“This is a happy shot!” says Hemmerich. “The shot just before and the shot just a few seconds later show nothing. The fireball was short-lived and I’m glad I caught it in this 2-second exposure.”

Dozens of reliable images and videos of the impact have surfaced in the days since the eclipse. Analyzing one sharp image taken by Christian Fröschlin of the Netherlands, geologist Justin Cowart has estimated the selenographic coordinates of the impact site: 29.47S, 67.77W +/- 4km. This puts it just to the west of the lunar crater Lagrange H. NASA’s Lunar Reconnaissance Orbiter may be able to use such coordinates to target its cameras and photograph the crater.

Meteoroids hit the Moon all the time. Literally. NASA has been observing impact flashes since 2005. Recently, other groups in Europe have joined the hunt. Flashes are typically recorded once every 2 to 3 hours of observing time. Impactors range in size from softballs to boulders, liberating energies equal to tons of TNT when they strike.


Above: The impact flash, photographed by Hunter McWilliams of Lubbock, Texas

The rare thing about this strike is that it was photographed during a full Moon, when lunar glare usually overwhelms the glow of any fireball. During the eclipse, Earth’s shadow turned lunar day into almost-night for an hour, allowing the fireball to be seen.

Readers, were you taking pictures of the eclipse around 04:41 UT? Check your photos. You might have captured an explosion. Submit images here.

Realtime Eclipse Photo Gallery

Earth’s Shifting Magnetic Pole May be Confusing Your Cell Phone

Jan. 16, 2019: Pick up your cell phone and look at it. That rectangular marvel of modern technology contains thousands of lines of code. Among them is the World Magnetic Model (WMM)–a program that helps your phone navigate.  And it’s in a bit of trouble. Researchers have announced that the WMM needs an emergency update because Earth’s magnetic field is changing.

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Savvy backcountry hikers have long known that compass needles don’t really point north. The magnetic north pole is displaced hundreds of miles from the true north pole and, to make matters worse, it wanders unpredictably from year to year. To find true north in the continental USA, you have to correct compass directions by as much as 20 degrees using a special “declination table.”

The World Magnetic Model is a computer program that makes this correction for you. It improves the navigation of devices ranging from nuclear submarines to common smartphones.

“The WMM is the standard magnetic model used for navigation by organizations such as NATO, the Ministry of Defence, and the US Department of Defense, and also by smartphone operating systems such as Android and iOS,” explains Will Brown of the British Geological Survey’s Geomagnetism Team, which produces the model in collaboration with NOAA of the USA.

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“When you open your smartphone’s map app, you may see an arrow pointing which way you’re facing, and there’s something quite clever going on underneath,” he continues. “Your phone contains a magnetometer that is measuring the Earth’s magnetic field. In order to make sense of this information, Android and iOS operating systems use the WMM to correct the measurements to true north.”

Normally the World Magnetic Model is updated every 5 years. For decades that’s been often enough to track natural changes in our planet’s magnetism caused by fluctuations in Earth’s molten core. But suddenly things are changing faster than before.

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Annual rate of change of declination for 2015.0 to 2020.0 from the World Magnetic Model (WMM2015). This information is about to be updated by a new WMM.

“Since late 2014, Earth’s core field has varied in an unpredicted, and currently unpredictable, manner [including a sudden change in declinaton called a ‘geomagnetic jerk‘ in 2014/2015],” says Brown. “The aim of the WMM is to be globally accurate within 1 degree of declination, but we were going to exceed that limit in only 3 years.” That’s why, for the first time, they are issuing an update to the WMM before the usual 5 year mark in 2020.

The new model is based data from a global network of 160 surface observatories and satellites in low-Earth orbit such as ESA’s Swarm mission. It was supposed to be released on Jan. 15th but has been delayed until Jan. 30th because of the partial shutdown of the US government.