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NEXT STOP, SATURN: Two nights ago, the Moon passed by Venus. Tonight, it's visiting Saturn. Step outside after sunset to find the ringed planet not far from the 22% illuminated lunar crescent: sky map.
GRAVITY WAVES ABOVE HURRICANE MATTHEW: Powerful Hurricane Matthew is scouring the islands of the Caribbean with 145 mph winds. Orbiting high above the tempest in the darkness of space, the NOAA/NASA Suomi NPP satellite has observed the storm's ripple effect on the upper atmosphere:
These ripples are called "gravity waves"--essentially, waves of pressure and temperature excited by the upward motion of air from the storm below. Gravity does not vary inside these waves; instead, they get their name from the fact that gravity acts as a vertical restoring force that tries to restore equilibrium to up-and-down moving air. Similar patterns have been observed above powerful thunderstorms.
Matthew's gravity waves are visible from the ground as well. Frankie Lucena of Cabo Rojo, Puerto Rico, captured them in his recent snapshots of sprites above the hurricane:
"Steven Miller of Colorado State University was kind enough to prepare these images for me to confirm that my sprite photo did contain gravity waves," says Lucena. "My location in southwestern Puerto Rico is noted in the satellite image above. By pointing my camera at the lightning, I also caught the waves."
Left to themselves, gravity waves would be invisible to the human eye. We see them, however, because they impress their patterns upon a luminous phenomenon called "airglow." Learn more about that in the next article, Amazing Airglow over Easter Island.
Realtime Space Weather Photo Gallery
RED AIRGLOW OVER EASTER ISLAND: Not every colorful light in the night sky is an aurora. Especially not in the South Pacific. Yuri Beletsky was on a beach in Easter Island, Chile, two nights ago when the starry canopy turned red:
"There was no fire," says Beletsky. "This is an amazing display of airglow."
Airglow is aurora-like phenomenon caused by chemical reactions in the upper atmosphere. Human eyes seldom notice the faint glow, because it is usually very faint, but it can be photographed on almost any clear dark night, anywhere in the world.
Beletsky is a veteran photographer of airglow, having captured it dozens of times from sites in Chile and the South Pacific. "The intensity of airglow varies, and sometimes it can be more prominent, as it was on Oct. 2nd," he says.
The curious thing about Beletsky's photo is not the intensity of the airglow, but rather its color--red. Airglow is usually green, the color of light from oxygen atoms some 90 km to 100 km above Earth's surface. Where does the red come from? Instead of oxygen, OH can produce the ruddy hue. These neutral molecules (not to be confused with the OH- ion found in aqueous solutions) exist in a thin layer 85 km high where gravity waves often impress the red glow with a dramatic rippling structure.
Realtime Airglow Photo Gallery
Realtime Sprite Photo Gallery
Realtime Aurora Photo Gallery
| ||Cosmic Rays in the Atmosphere |
Updated: Sept. 29 2016 // Next Flight: Oct. 1, 2016
Sept. 20, 2016: 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.
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 Oct. 5, 2016, the network reported 39 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 October 5, 2016 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.
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