|
SOLAR ACTIVITY:
There are no sunspots today, but that doesn't mean the sun is quiet.
Astronomers are monitoring a lively
prominence flying
away from the southwestern limb of the sun. If you have a solar
telescope, take a look.
COMET LULIN UPDATE:
Comet Lulin is approaching Earth for a 38-million-mile
close encounter on Feb. 24th. Veteran observer Mariano Ribas sends
this report from Argentina: "Today at 4 a.m. in Buenos Aires,
I observed the comet with my 90 mm refractor (25x). It is much brighter
than it was just a few nights ago. I estimate the magnitude at +5.6.
If this brightening continues, Lulin could reach magnitude +5.0
or even brighter during its closest approach next week."
Lulin has brightened so much, telescopic amplification is no longer
needed to photograph it. Using an off-the-shelf digital camera,
Alex Roca of Hortoneda, Spain, caught the comet passing 4th-magnitude
star theta Virginis on Feb. 17th:
"I mounted the camera, a Nikon
D40, on the back of my telescope to track the stars," he
says. "Otherwise, the telescope played no part in this 10 minute
exposure."
Comet
Lulin Photo Gallery
[Comet
Hunter Telescope] [NASA's
story] [ephemeris]
FIREBALL MANIA:
Runners in Sunday's Austin marathon were astonished when a brilliant
fireball raced across the Texas sky in broad daylight. The extremely-bright
meteor descended at 11 am CST on Feb. 15th less than a day after
the FAA reportedly warned U.S. pilots to watch for "falling
space debris" from the recent satellite
collision between Iridium 33 and Kosmos 2251. Click on the image
to launch a News 8 Austin video:
Click
to view fireball video
What you just saw was not satellite debris. The high speed of the
fireball in the News 8 video is typical of a natural meteoroid hitting
Earth's atmosphere at tens of km/s. Orbital debris, on the other
hand, should crawl across the sky at a fraction of that speed. Astronomer
Bill Cooke of NASA's Meteoroid Environment Office has reviewed the
video and confirms "it's a natural meteor,
definitely." According to his analysis, the source of the fireball
was a meter-class asteroid traveling at about 20 km/s.
Fireball mania started on Friday the 13th, around 10 p.m. EST,
when people in central Kentucky heard loud booms, felt their houses
shake, and saw a fireball streaking through the sky: reports.
"The world appeared to explode--in green!" said one eyewitness.
Once again, this appears to be a natural event caused by a meteoroid.
Iridium 33 and Kosmos 2251 collided at a speed of about 10 km/s
or 22,000 mph. None of the surviving fragments should have been
big enough to shake houses in Kentucky. Furthermore, US Space Command,
which monitors objects in Earth orbit, has not announced a reentry
over Kentucky on Feb. 13th.
Just hours before the Kentucky event, around 20:03 UT on Feb. 13th,
multiple cameras in Italy recorded a fireball some 10 times brighter
than a full Moon. Astronomer Diego Valeri sends this image from
the town of Rieti:
Click to
view fireball video (Note: DivX
required)
Ferruccio Zanotti of Ferrara, Italy, recorded that same
fireball and two
others. Italian
scientists are plotting the trajectory of the brightest fireball
to estimate where it might have hit the ground; a meteorite hunt
will soon be underway.
Although it is tempting to attribute the Kentucky and Italian fireballs
to debris from the Feb. 10th collision of the Iridium 33 and Kosmos
2251 satellites, they seem to be meteoroids, not manmade objects.
Are we experiencing a "fireball shower?" Not necessarily.
Meteoroids hit Earth every day. The daily fireballs they produce,
however, are seldom reported: 70% streak over uninhabited ocean;
half appear in glaring daylight; many are missed because people
are asleep, at work, or not looking up. This current spate of fireballs
could simply be a few ordinary, random meteoroids that have attracted
extraordinary attention because of the recent satellite collision.
The jury is still out.
Stay tuned for updates.
February
2009 Aurora Gallery
[Previous Februaries: 2008,
2007,
2006,
2004,
2003,
2002]
Explore
the Sunspot Cycle
|
