Turn your cell phone into a field-tested satellite tracker. Works for Android and iPhone. | | | INCOMING CME: A coronal mass ejection (CME) propelled toward Earth by the X2-flare of Feb. 15th should arrive during the late hours of Feb. 17th--that's today. A moderately strong geomagnetic storm is likely when it arrives. High-latitude sky watchers should be alert for auroras after nightfall. NASA's researchers have made a time-lapse movie of the Feb. 17th explosion. Click on the arrow to play the movie, then scroll down for commentary: 
This is a composite of data from two spacecraft: SOHO and the Solar Dynamics Observatory (SDO). SDO took the golden picture in the middle; it's an extreme ultraviolet image of the sun. A flash of UV radiation centered on sunspot 1158 marks the biggest solar flare since Dec. 2006. SOHO took the red picture on the outside; it's a coronagraph image. The CME en route to Earth now is visible as a willowy cloud flying away from the solar disk. More images and movies of this event may be found here. MYSTERIOUS SUN HALOES: Most sun haloes are circles. They surround the sun when sunbeams hit ice crystals in the air. The haloes this week in Finland, however, were not circular. Olli Leivo sends this picture from Lahti in southern Finland: 
Photo details: Canon EOS 550D, 50mm, f11, 1/250s. More images: #1, #2, #3, #4
"Finland has had a spate of elliptical halos over the last few days produced by ice crystals precipitating out of low clouds. The ones Leivo photographed are superb," says atmospheric optics expert Les Cowley. "Elliptical halos are rare and we do not understand how they are formed. A popular theory is that hexagonal plate-shaped crystals with very blunt pyramidal ends make them. But ray tracing simulations using these crystals do not reproduce the halo’s fine detail properly. Moreover, these crystals are physically unrealistic because crystal faces follow lines of atoms in the crystal lattice – blunt pyramidal ends do not! The mystery remains."
February 2011 Aurora Photo Gallery
[previous Februaries: 2010, 2009, 2008, 2007, 2006, 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 February 17, 2011 there were 1198 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 | | 
