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AURORA WATCH: High latitude sky watchers should be alert for auroras. NOAA forecasters estimate a 40% chance of geomagnetic activity during the next 48 hours, when a solar wind stream is expected to buffet Earth's magnetic field. A coronal mass ejection (movie) detected by NASA's STEREO probes on April 9th could also reach Earth and contribute to the display on April 11th. [aurora gallery]
GRAND FILAMENT: A magnificent filament of magnetism is curling around the sun's southeastern quadrant today. Measuring more than 700,000 km from end to end, the vast structure is about twice as long as the separation between Earth and the Moon. Arrows trace the filament's meandering path in this extreme UV image from NASA's Solar Dynamics Observatory:
It's not easy for such a filament to remain suspended indefinitely above the stellar surface, and indeed a collapse is possible. Filaments falling onto the sun can trigger explosions called "Hyder flares." Is one in the offing? Readers with solar telescopes are encouraged to monitor developments.
SUN HALO: Today in upstate New York, amateur astronomer Mike Taormina aimed his solar telescope at the Grand Filament--but he saw something else instead. "A thin layer of clouds created a beautiful circular halo around the sun." He stepped back from the eyepiece and took this picture:
Sun haloes are caused by ice crystals in high clouds. With its abundance of wispy cirrus, northern spring is a good time to see the phenomenon. Keep an eye out for luminous circles and other forms around the sun.
more images: from Rana Khan of Salt lake, Kolkata, India; from Sandra Kelly of Shoreline, Washington
UPDATED: April 2011 Aurora Gallery
[previous Aprils: 2010, 2009, 2008, 2007, 2006, 2005, 2004, 2003, 2002]
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 April 9, 2011 there were 1214 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 |
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