From: LARRY KLAES (ljk4_at_msn.com)
Date: Thu May 29 2003 - 11:34:02 PDT
----- Original Message -----
From: Cary Oler
Sent: Thursday, May 29, 2003 8:50 AM
To: sun-earth_at_SkyandTelescope.com
Subject: AstroAlert: Another X-Class Solar Flare Rips from Sunspot Complex 10365
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This Is SKY & TELESCOPE's AstroAlert for Sun-Earth Interactions
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A s t r o A l e r t
Sun-Earth Alert
Solar Terrestrial Dispatch
http://www.spacew.com
Supporting Imagery and Movies are available at:
http://www.spacew.com/astroalert.html
29 May 2003
ANOTHER X-CLASS FLARE RIPS FROM SUNSPOT COMPLEX 10365
Region 10365 (nicknamed '365' by space weather forecasters) is
continuing to flex its "muscles". At 9:06 pm EDT on 28 May (01:06 UTC on
29 May) this region spawned its third major X-class solar flare in less than
36 hours.
The spot complex has continued to grow in size and magnetic complexity
over the last 24 hours despite the intensity of the solar flaring, which
often brings greater stability to volatile sunspot groups. Additional
major solar flares are possible over the next several days.
The full-halo (Earthward-directed) coronal mass ejection associated with
this latest X-class flare is expected to impact the Earth sometime in the
late-evening hours of 30 May for North American observers (or the early UTC
hours of 31 May for other international locations). The arrival of this
disturbance will effectively prolong the anticipated disturbed geomagnetic
and auroral conditions that may pre-exist at that time - caused by the
arrival of the coronal mass ejections associated with yesterday's X-class
solar flares.
Keep your eye's toward the skies over the next several evenings. Rapidly
updated and current information is available and will be provided through the
forecast notes at Solar Terrestrial Dispatch (www.spacew.com). Software is
also available through this site to significantly help observers to know when
to look for auroral activity. Current sightings of auroral activity are also
available through the Global Auroral Activity Observation Network at:
http://www.spacew.com/www/auroras.html. Imagery of recently observed auroral
activity can also be found in the image gallery at:
http://www.spacew.com/gallery. Real-time images of the Sun and flare activity
are available from: http://www.spacew.com/sunnow
Observers with telescopes equipped with protective equipment for viewing
the Sun safely may want to watch the leading large sunspots of this region
for possible white-light solar flares. White-light flares are relatively rare
events that only accompany the most powerful solar flares. Richard Carrington
and Richard Hodgson were the first astronomers to independently observe a
white-light solar flare on 1 September 1859. As Richard Carrington later
related,
"While engaged in the forenoon of Thursday, September 1, in taking my
customary observation of the forms and positions of the solar spots, an
appearance was witnessed which I believe to be exceedingly rare. The image of
the sun's disk was, as usual with me, projected on to a plate of glass coated
with distemper of a pale straw color, and at a distance and under a power
which presented a picture of about 11 inches diameter. I had secured diagrams
of all the groups and detached spots, and was engaged at the time in counting
from the chronometer and recording the contacts of the spots with the
cross-wires used in the observation, when within the area of the great north
group (the size of which had previously excited great remark), two patches of
intensely bright and white light broke out, in the positions indicated in
fig. 1 ... My first impression was that by some chance a ray of light had
penetrated a hole in the screen attached to the object glass, for the
brilliancy was fully equal to that of direct sun-light; but by at once
interrupting the current observation, and causing the image to move ... I saw
I was an unprepared witness of a very different affair. I therefore noted
down the time by the chronometer, and seeing the outburst to be very rapidly
on the increase, and being somewhat flurried by the surprise, I hastily ran
to call some one to witness the exhibition with me, and on returning within
60 seconds, was mortified to find that it was already much changed and
enfeebled. Very shortly afterwards the last trace was gone. In this lapse of
5 minutes, the two patches of light traversed a space of about 35,000 miles."
(Excerpt from: Description of a Singular Appearance seen in the Sun on
September 1, 1859, by Richard C. Carrington, Monthly Notices of the Royal
Astronomical Society, vol. 20, 13-15, 1860.
This remarkable account was, fortunately, observed by a fellow observer
(Richard Hodgson) down the road from Carrington (both of whom resided in
England). His account was similar to Carringtons:
"While observing a group of solar spots on the 1st September, I was suddenly
surprised at the appearance of a very brilliant star of light, much brighter
than the sun's surface, most dazzling to the protected eye, illuminating the
upper edges of the adjacent spots and streaks, not unlike in effect the
edging of the clouds at sunset; the rays extended in all directions; and the
centre might be compared to the dazzling brilliancy of a bright star. It
lasted for some five minutes, and disappeared instantaneously about 11.25
am." (Monthly Notices of the Royal Astronomical Society).
About 17 hours after these men observed the white-light flare on the
Sun, one of the largest geomagnetic and auroral storms in history commenced.
This translates roughly into a coronal mass ejection that was travelling
Earthward at an average velocity in excess of 2,400 kilometers per second
(8.6 million km/hour or about 5.4 million miles per hour - a phenomenal
velocity). By comparison, most coronal mass ejections travel outward at
velocities less than 500 to 600 km/sec. So this was a very rare event.
The observations made by Carrington and Hodgson are typical of
white-light flares. Although the brilliancy of the white-light enhancements
may vary from one flare to another, observers often detect movement in the
white-light emissions - a common feature of solar flares. And all white-light
flares are fleeting events - lasting anywhere from seconds to only a few
minutes. This explains why these types of events are rarely observed.
As we continue to very gradually decline from the solar maximum, solar
flares capable of producing white-light enhancements will also gradually
wane. Region 365 therefore provides an interesting opportunity to perhaps
witness a white-light event during the declining phase of the current solar
cycle.
** End of the AstroAlert Bulletin **
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