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UARS
RE-ENTRY UPDATE: NASA's UARS satellite
is making its last orbits around Earth. Orbital
elements published today by the US Strategic Command
suggest that re-entry could occur during the early
hours of Saturday morning. "For now, it looks
like 00:00 - 04:00 UTC on Sept. 24,"
says satellite tracking expert Ted Molczan, "but
it could well happen even later. UARS will pass
over North America and Europe several times during
this period, but it will spend most of its time
over oceans and sparsely populated land." Stay
tuned for updates and meanwhile keep
an eye out for the doomed satellite. [latest
NASA statement]
The Federal Aviation Administration
has issued the following Notice to Airmen
(NOTAM): "Aircraft are advised that
a potential haard may occur due to reentry of satellite
UARS into Earth's atmosphere. FAA is working with
the Department of Defense and NASA to ensure the
most current re-entry information is provided to
operators as quickly as possible. Further NOTAMS
will be issued if specific information becomes available
indicating a United States airspace impact. It is
critical that all pilots/flight crew members report
any fallinf space debris to the appropriate ATC
facility. The Domestic Events Network telephone
202-493-5107 is the FAA coordination facility. CREATED:
23 SEP 18:33 2011"
EQUINOX
SUNRISE: The seasons changed this
morning at 5:05 a.m. EDT when the Sun crossed the
celestial equator heading south. Fall began in the
Northern Hemisphere, spring in the Southern Hemisphere.
Geoffrey Wyatt of Sydney, Australia, woke up early
to watch the equinox sun rise over Watson's Bay:
"This is how the first day of
spring began in Australia," says Wyatt. "Recent
fires in the Sydney area have contributed to redder
than usual sunrises and sunsets. Temperature
gradiants over the water produced the added
bonus of a miraged
sun."
Happy Equinox!
more images: from
Monika Landy-Gyebnar of Balatonfured, Hungary
AURORAS
UNDERFOOT: Solar activity is picking
up, and no one has a better view of its effect on
Earth than the crew of the International Space Station.
During a geomagnetic storm on Sept. 17th, astronauts
recorded a must-see movie of auroras dancing underfoot:
Taken over the southern Indian Ocean,
the movie spans a 23-min period from 17:22:27 to
17:45:12 GMT on Sept. 17.
Note how the underbelly of the space
station glows green from the reflected light of
the auroras below. Also, in the distance, Sirius
the dog star and Orion the Hunter can be seen rising
feet-first into the night sky.
The storm, which registered a moderate
6 on the 0-to-9 K-index
scale of geomagnetic disturbances, was caused by
a coronal mass ejection (CME) hitting Earth's magnetic
field. It was just a glancing blow, but with CMEs
that is often enough to spark bright auroras over
both ends of Earth. The space station was flying
over the southern hemisphere at the time of the
display. Observers in the northern hemisphere saw
it
too.
A similar storm could be in the offing
this week. Another CME is heading toward Earth,
and it appears likely to deliver a glancing blow
on Sept. 22nd around 23:00 UT. Sky watchers above
and below should be alert for auroras.
Aurora alerts: text,
voice.
September
2011 Aurora Gallery
[previous Septembers: 2010,
2009, 2008,
2007,
2006,
2005,
2004]
MAJOR
X-FLARE + CME: Yesterday, Earth-orbiting
satellites detected a long-duration X1.4-class solar
flare coming from sunspot 1302 on the sun's eastern
limb. The blast, which peaked at 1100 UT on Sept.
22nd, produced a significant coronal mass ejection
(CME). Using data from the SOHO-STEREO fleet of
spacecraft, analysts at the Goddard Space Weather
Lab have modeled the trajectory of the CME and concluded
that the body of the cloud will not hit Earth. A
minor glancing encounter with the outskirts of the
CME is, however, possible on Sept. 25th. [CME:
movie,
forecast
track]
X-flares of Solar Cycle 24:
There have been only a half-dozen X-flares since
the beginning of new Solar Cycle 24. Here is a complete
list so far, all in 2011: Feb. 15 (X2), March 9
(X1), Aug. 9 (X7), Sept. 6 (X2), Sept. 7 (X2), Sept.
22 (X1). Before these six, the previous X-flare
occured on Dec.14, 2006, (X1) during old Solar Cycle
23.
