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AURORA WATCH:
High-latitude sky watchers should be alert for auroras tonight.
A solar wind stream is buffeting Earth's magnetic field and
causing geomagnetic disturbances around the poles: more.
ASTEROID NEAR MISS:
On Nov. 6th at 2132 UT, asteroid 2009
VA barely missed Earth when it flew just 14,000 km above
the planet's surface. That's well inside the "Clarke
Belt" of geosynchronous satellites. If it had hit,
the ~6-meter wide space rock would have disintegrated in the
atmosphere as a spectacular fireball, causing no significant
damage to the ground. 2009 VA was discovered just 15 hours
before closest approach by astronomers working at the Catalina
Sky Survey.
WEEKEND FIREBALLS:
On Saturday, Nov. 7th, just as the sun was
setting over San Francisco Bay, a brilliant meteor glided
across the sky and disappeared into the sunset. Witnesses
say it was "slow-moving," "white and green,"
and that it left behind "a trail of smoke and sparkles
of debris." Alerted by a friend, Rick Baldridge of Campbell,
California, rushed outside and snapped this picture of the
fireball's aftermath:
"This was a rare event," says Baldridge.
"I have not seen a high altitude 'smoke' stream like
this for more than 20 years."
The fireball may have been a piece of periodic
Comet 2P/Encke. Right now, Earth is passing through a stream
of debris from the comet, and this is causing the annual Taurid
meteor shower, which peaks between Nov. 5th and 12th.
The display usually produces no more than about 5 meteors
per hour, but what it lacks in number, it makes up for in
dazzle. Taurids tend to be fireballs, bright enough to be
seen even in twilight skies. At the time of the Bay Area fireball,
the constellation Taurus was rising in the east, so the fireball's
identification as a Taurid seems probable, albeit not certain.
A few hours later in Ozark, Arkansas, amateur
astronomer Brian Emfinger photographed a definite Taurid:
movie.
"I estimate its brightness at around magnitude -10 (almost
200 times brighter than Venus)."
Sky watchers should be alert for Taurid fireballs
in the nights ahead. The best time to look is during the hours
around midnight when the constellation Taurus soars high overhead:
sky
map.
COMPLETE FOGBOW:
On Oct. 24th, Mila
Zinkova of San Francisco took an early morning stroll
along the beach. As her shadow stretched across the damp sand,
a ghostly white ring surrounded the dark form. "It was
a 360o fogbow--a very special sight," she
says.
Fogbows are close cousins of rainbows. The difference is
droplet size. Rainbows appear when sunlight
bounces in and out of large raindrops. The same type of
reflection produces
a fogbow, except fog droplets are much smaller. Small
droplets don't separate the colors of sunlight as widely as
large raindrops do. In a fogbow, therefore, the colors are
smeared together, producing a ghostly-white arc.
"Nearby I saw a
spiderweb," adds Zinkova. "The whole web was
covered with tiny fog droplets, the droplets that made fogbow
possible."
Only one question remains: Why is the fogbow a complete circle?
Most fogbows, like rainbows, display only their upper half.
Atmospheric optics expert Les Cowley has the answer: "All
fogbows would like to be a full circle centered on your shadow,
but usually there are insufficient tiny fog droplets near
the ground to make a bow bright enough to see. Here the dark
background helps to reveal it."
BONUS: weekend
solar images: from
Pete Lawrence of Selsey, West Sussex, UK; from
Alan Friedman of Buffalo, New York;
October
Northern Lights Gallery
[previous Octobers: 2008,
2007, 2006,
2004, 2003,
2002, 2001]
Explore
the Sunspot Cycle |
