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GREEN SKIES ON ST. PATRICK'S DAY? Today is St. Patrick's Day. Arctic sky watchers may be able to celebrate with a splash of green in the sky. A weak CIR is expected to hit Earth's magnetic field on March 17th. CIRs (co-rotating interaction regions) are transition zones between slow- and fast-moving streams of solar wind. Compressed magnetic fields in CIRs often do a good job of sparking auroras. Free: Aurora Alerts
BIG CORONAL HOLE TURNS TOWARD EARTH: A hole has opened in the sun's atmosphere, and it is turning toward Earth. NASA's Solar Dynamics Observatory is tracking the opening, which researchers call a "coronal hole" (CH):
Coronal holes are places--big places--where the sun's magnetic field opens up and allows solar wind to escape. A wide stream of solar wind flowing from this coronal hole is expected to reach our planet on March 23rd. The impact of the solar wind should produce magnetic activity around Earth's poles and could spark the first auroras of northern spring. Stay tuned. Free: Aurora Alerts
Realtime Aurora Photo Gallery
NEUTRONS ON A PLANE: It is well known that air travelers are exposed to cosmic rays. High-energy particles and photons from deep space penetrate Earth's atmosphere and go right through the hulls of commercial aircraft. This has prompted the International Commission on Radiological Protection (ICRP) to classify pilots and flight attendants as occupational radiation workers.
Most studies of this problem focus on ionizing radiation such as x-rays and gamma-rays. Yesterday, Spaceweather.com turned the tables and measured neutrons instead. With help from the students of Earth to Sky Calculus, we used a pair of bubble chambers to monitor neutron activity inside a Scandinavian Airlines jetliner. In this photo taken 35,000 feet above Greenland, each bubble shows where a neutron passed through the chamber and vaporized a superheated droplet:
During the 11-hour flight we measured almost 20 uSv (microsieverts) of radiation from neutrons. That's more than the dose from X-rays and gamma-rays combined. (We measured X-rays and gamma-rays using other sensors.) This confirms that neutrons are an important form of aviation radiation, providing much of the biologically effective radiation dose at altitudes of interest to air travelers and space tourists.
Earlier in the week, we flew these same bubble chambers to the Arctic stratosphere using a space weather balloon. Interestingly, the 11-hour plane flight yielded 6 times more neutrons than the shorter (2 hour) but far higher (97,000 ft) balloon flight. Stay tuned for more data from our week-long trip to the Arctic Circle.
Realtime Venus Photo Gallery
Realtime Space Weather Photo Gallery
Realtime Comet Photo Gallery
Every night, a network of NASA all-sky cameras
scans the skies above the United States for meteoritic fireballs. Automated software maintained by NASA's Meteoroid Environment Office calculates their orbits, velocity, penetration depth in Earth's atmosphere and many other characteristics. Daily results are presented here on Spaceweather.com.
On Mar. 17, 2017, the network reported 18 fireballs.
In this diagram of the inner solar system, all of the fireball orbits intersect at a single point--Earth. The orbits are color-coded by velocity, from slow (red) to fast (blue). [Larger image] [movies]
Potentially Hazardous Asteroids (PHAs
) are space rocks larger than approximately 100m that can come closer to Earth than 0.05 AU. None of the known PHAs is on a collision course with our planet, although astronomers are finding new ones
all the time.
On March 17, 2017 there were potentially hazardous asteroids. Notes: LD means "Lunar Distance." 1 LD = 384,401 km, the distance between Earth and the Moon. 1 LD also equals 0.00256 AU. MAG is the visual magnitude of the asteroid on the date of closest approach.
| ||Cosmic Rays in the Atmosphere |
Readers, thank you for your patience while we continue to develop this new section of Spaceweather.com. We've been working to streamline our data reduction, allowing us to post results from balloon flights much more rapidly, and we have developed a new data product, shown here:
This plot displays radiation measurements not only in the stratosphere, but also at aviation altitudes. Dose rates are expessed as multiples of sea level. For instance, we see that boarding a plane that flies at 25,000 feet exposes passengers to dose rates ~10x higher than sea level. At 40,000 feet, the multiplier is closer to 50x. These measurements are made by our usual cosmic ray payload as it passes through aviation altitudes en route to the stratosphere over California.
What is this all about? Approximately once a week, Spaceweather.com and the students of Earth to Sky Calculus fly space weather balloons to the stratosphere over California. These balloons are equipped with radiation sensors that detect cosmic rays, a surprisingly "down to Earth" form of space weather. Cosmic rays can seed clouds, trigger lightning, and penetrate commercial airplanes. Furthermore, there are studies ( #1, #2, #3, #4) linking cosmic rays with cardiac arrhythmias and sudden cardiac death in the general population. Our latest measurements show that cosmic rays are intensifying, with an increase of more than 12% since 2015:
Why are cosmic rays intensifying? The main reason is the sun. Solar storm clouds such as coronal mass ejections (CMEs) sweep aside cosmic rays when they pass by Earth. During Solar Maximum, CMEs are abundant and cosmic rays are held at bay. Now, however, the solar cycle is swinging toward Solar Minimum, allowing cosmic rays to return. Another reason could be the weakening of Earth's magnetic field, which helps protect us from deep-space radiation.
The radiation sensors onboard our helium balloons detect X-rays and gamma-rays in the energy range 10 keV to 20 MeV. These energies span the range of medical X-ray machines and airport security scanners.
The data points in the graph above correspond to the peak of the Reneger-Pfotzer maximum, which lies about 67,000 feet above central California. When cosmic rays crash into Earth's atmosphere, they produce a spray of secondary particles that is most intense at the entrance to the stratosphere. Physicists Eric Reneger and Georg Pfotzer discovered the maximum using balloons in the 1930s and it is what we are measuring today.
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