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NOCTILUCENT CLOUDS VANISH: Summer is the season for noctilucent clouds (NLCs), and now that northern summer is coming to an end, so are the clouds. NASA's AIM spacecraft may have spotted the last wisp of electric blue over Greenland on Aug. 27th. Data from Aug. 28th show no NLCs around the Arctic Circle. If the deficit continues, attention will shift to the southern hemisphere where Antarctic noctilucent cloud season begins in November. Stay tuned for updates.
ALMOST-BLANK SUN: The sunspot number is plummeting, and the Earth-facing side of the sun is almost blank. Scan this image, taken on Sept. 1st by NASA's Solar Dynamics Observatory, to see how many dark cores you can find:
There are only a few tiny spots, circled here. Not one of them has the type of unstable magnetic field that harbors energy for strong flares. As a result, the sun's X-ray output is flatlining. NOAA forecasters estimate a 5% chance of M-flares and no more than a 1% chance of X-flares during the next 24 hours. Solar flare alerts: text or voice
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NORTHERN LIGHTS, NO PARKA REQUIRED: Arctic skies are dimming again after a rare burst of summer auroras. From Aug. 26th to 29th, Earth passed through a region of space where the interplanetary magnetic field (IMF) connected with our own magnetic field, opening a crack in Earth's magnetosphere. Solar wind poured in to fuel displays like this one over Anchorage, Alaska:
"The sky was full of lights," says Anthony Madden, who took the picture from Lake Hood Airport on Aug. 28th. "The best part was, it was warm enough that I did not need a parka."
The storms are subsiding now, but they could return on Sept. 2nd when Earth crosses through a fold in the heliospheric current sheet. This is called a "solar sector boundary crossing," and NOAA forecasters estimate a 70% chance of polar geomagnetic storms when it occurs. Aurora alerts: text or voice
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THE EDGE OF THE SUN: Giant sunspot AR2403 has departed, leaving the face of the sun mostly blank. Amateur astronomer Sergio Castillo of Corona, CA, decided to look for something else to photograph. "My search didn't take long," he says, "because there are plenty of beautiful prominences on the solar limb." This is what he saw on Aug. 29th:
The massive structure is more than 30,000 km tall and 100,000 km wide. Planet Earth could fit through the central arch with room to spare. (Croquette, anyone?)
Prominences are plumes of hot plasma held aloft by magnetic fields on the sun. Typical prominences last a few days, until the underlying magnetic supports become unstable and collapse. This one has already been visible for several days, so a photogenic explosion could be in the offing. Amateur astronomers with solar telescopes and filters are encouraged to monitor developments.
THE SUN SWALLOWS A COMET: On Friday, Aug.28th, the sun swallowed a comet. The Solar and Heliospheric Observatory (SOHO) spotted the icy vistor from the outer solar system making a headlong plunge into our star. One comet went in; none came out. Click to play the movie:
Heated by the sun at point blank range, the comet's fragile ices vaporized, leaving at most a "rubble pile" of rock and gravel scattered along its sungrazing orbit. Any remains are invisible from Earth.
The comet, R.I.P., was probably a member of the Kreutz family. Kreutz sungrazers are fragments from the breakup of a single giant comet many centuries ago. They get their name from 19th century German astronomer Heinrich Kreutz, who studied them in detail. Several Kreutz fragments pass by the sun and disintegrate every day. Most, measuring less than a few meters across, are too small to see, but occasionally a bigger fragment like this one (~10 m to 50 m) attracts attention.
Because of their common parentage, sungrazers often come in clusters. For this reason, it wouldn't be surprising to find yet another one in the offing. Monitor Karl Battam's Sungrazing Comet twitter feed for more sightings.
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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 Aug. 31, 2015, the network reported 17 fireballs.
(16 sporadics, 1 alpha Aurigid)
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 August 31, 2015 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.
| ||The official U.S. government space weather bureau |
| ||The first place to look for information about sundogs, pillars, rainbows and related phenomena. |
| ||Researchers call it a "Hubble for the sun." SDO is the most advanced solar observatory ever. |
| ||3D views of the sun from NASA's Solar and Terrestrial Relations Observatory |
| ||Realtime and archival images of the Sun from SOHO. |
| ||from the NOAA Space Environment Center |
| ||the underlying science of space weather |
| ||Web-based high school science course with free enrollment |