Are we alone? Your iPhone has the answer. Download the all-new Drake Equation app to calculate the population of the Milky Way.
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RE-ENTRY ALERT: UARS, a NASA satellite the size of a small bus, will re-enter the atmosphere later this week. Best estimates place the re-entry time during the late hours of Sept. 23rd over a still-unknown region of Earth. "It is still too early to predict the time and location of re-entry," says NASA. "Predictions will become more refined over the next two days."
The disintegration of UARS is expected to produce a fireball that could be visible even in broad daylight. Not all of the spacecraft will burn up in the atmosphere, however; according to a NASA risk assessment, as many as 26 potentially hazardous pieces of debris could be scattered along a ground track some 500 miles long. The same report puts the odds of a human casualty at 1 in 3200.
On Sept. 15th, astrophotographer Theirry Legault video-recorded the doomed satellite during one of its last passes over France:
Photo details: Celestron 14" EdgeHD, Takahashi EM400 mount modified for fast tracking. Range to UARS: 252 km.
"The satellite appears to be tumbling, perhaps because a collision with satellite debris a few years ago," notes Legault. "The variations in brightness are rapid and easily visible to the human eye." (Other observers have reported UARS flashes almost as bright as Venus.)
For last-chance sightings of this brightly flashing satellite, please check the Simple Satellite Tracker or download the Satellite Flybys app for your smartphone.
more images: from Oscar Martín Mesonero of Madrid, Spain
AURORA WATCH: "Last night was magical here in Inari, Finland," reports Andy Keen. "The moonlight, clouds and stars framed a beautiful display of aurora borealis." He photographed the scene just after midnight:
More midnight magic could be in the offing. A coronal mass ejection (CME) is heading toward Earth and it could deliver a glancing blow to our planet's magnetic field on Sept. 22th around 23:00 UT. High-latitude sky watchers should be alert for auroras when the CME arrives. Aurora alerts: text, voice.
more images: from Andrew Hindley of Inari, finland
September 2011 Aurora Gallery
[previous Septembers: 2010, 2009, 2008, 2007, 2006, 2005, 2004]
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 September 21, 2011 there were 1244 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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