End of Days à
la Barbeque?
Solar cycle ups and downs continues to
mystify scientists...
No massive
events are in the forecast, yet
Dec.
16, 1999: A popular rumor making the rounds on the Internet
is that on Jan. 1, 2000, the sun will let loose with a
powerful coronal mass ejection (CME) that will zap important
communications satellites and short-circuit terrestrial
power grids.
Not! The sun indeed is becoming more
active, but it's nothing new.
Right: Against an X-ray image of the sun
taken on Dec. 9, a graph traces the actual sunspot average
for Cycle 23 (jagged line) against the predictions (center
curve) of the NASA/Marshall team. The anticipated maximum
and minimum ranges are given by the dotted lines. Links to 1283x997-pixel,
563KB JPG. Credit: NASA/Marshall Space Flight Center and
the Yohkoh Soft X-ray Telescope team.
"The sun's been doing this for a
long, long time," said Dr. David Hathaway, solar
physics group leader at NASA's Marshall Space Flight Center.
And even though the sun is climbing towards the peak of yet
another sunspot cycle maximum, "This cycle is a little
different from what we've seen, but not out of the ordinary.
For us on Earth it's going to be life as usual.
Hathaway is one of several scientists who
will talk about the current solar maximum in a panel
discussion at the American Geophysical Union's annual fall
meeting in San Francisco.
"The big difference for us is our
increasing dependence on technology in general and on
space-based technology in particular. Certainly it's not
going to wipe out the planet although it may affect a
satellite or two."
The story about a powerful CME is gaining
wide circulation on the Internet, largely because there are
elements of truth to it. The solar cycle is climbing towards
maximum. CMEs can generate geomagnetic storms that disrupt
or damage satellites. Geomagnetic storms have overloaded the
power grid in the American northeast. And then there was the
"planet buster" comment offered in jest but taken
seriously by a few people.
Here are the basics. The sun has an
11-year-long cycle during which an increasing number of
spots appear at high latitudes and drift towards the
equator. The spots are actually regions of intense magnetic
activity where the solar atmosphere is slightly cooler than
the surrounding atmosphere. This makes the regions appear
black when viewed through filters that reduce the light to
bearable intensities for cameras and eyes. [Note: never look
at the sun through anything but filters designed just for
that purpose. Make sure the filters have no scratches or
other damage that can pass direct sunlight.]
The length of the cycle isn't fixed at 11
years; that's just the average. (Further, solar physicists
often think in terms of a 22-year cycle since the sun's
magnetic poles reverse direction every 11 years.) We are now
in the start of Cycle 23, the 23rd since reliable
observations became available.
"It looks like this cycle, while
bigger than usual, is certainly no record setter,"
Hathaway continued. "In fact, it keeps looking wimpier
than expected."
That's because Hathaway and two other
scientists at NASA/Marshall earlier this year published a
means of predicting sunspot numbers ("A synthesis of
solar cycle prediction techniques," Journal of
Geophysical Research, Oct. 1, 1999). Their model does a
credible job of predicting the sunspot numbers for the first
36 months of cycles 19 through 22. (Scientists often make
what appear to be after-the-fact predictions in order to
test new math models of how things should work.) Three of
the predictions are "dead on," and the fourth is
close.
The potential for a CME to cause a
geomagnetic storm that disrupts life on Earth is very real,
though, as demonstrated several times. The 1989 power
blackout in the American northeast and Canada was triggered
by a geomagnetic storm that overloaded one part of the power
grid and caused a blackout to cascade through the system.
Several satellites have been disrupted, and at least one or
two killed, by radiation enhanced by geomagnetic storms.
For these reasons, operators of
satellites, power systems, pipelines, and other sensitive
systems keep an eye on solar-terrestrial activities by way
of the Space Environment Center in Boulder, Colorado. The
center, in turn, collects data from ground and orbiting
solar telescopes, magnetometers, and other instruments, and
posts warnings on the web and through direct contact.
Systems operators can then take the
appropriate measures. Satellite controllers may shut down
all but the most basic housekeeping systems to prevent
electrical charging that could short vital systems. Utility
companies can isolate portions of a power grid so a blackout
does not cascade across the grid.
But
beyond making a brighter aurora, a powerful CME won't have
any noticeable effect on the ground. On June 4 the Solar and
Heliospheric Observatory (SOHO) saw a large CME that Dr.
Richard Fisher of NASA's Goddard Space Flight Center called
"a real planet-buster." The comment was meant in
jest, but was picked up and circulated by traditional news
media and the rumor mill. It was far less than a blast from
Darth Vader's Death Star.
Right: This is the "planet
buster" that wasn't. On June 1, 1999, the LASCO
coronagraph on SOHO observed a massive cloud of plasma
leaving the sun. Its apparent brightness is caused by the
sun's brilliant disk being blocked by the telescope optics.
The CME is actually quite faint. Credit: ESA/SOHO.
Where the sun could deal us a surprise is
an event known as the Maunder Minimum. During 1645-1715, the
Northern Hemisphere was locked in a "Little Ice
Age." At the same time, no sunspots were observed.
Because astronomy was so primitive, that's
about the limit of what we know from then. It was even
forgotten until 19th century English astronomer E.W. Maunder
investigated it in 1890. Other minima are believed to have
occurred, but sunspot records don't exist before 1610 (The
effects of the Sporer Minimum, 1460-1550, can be seen early
in the movie "Orlando" with ice skating and even a
full staged play on the frozen Thames River). These studies
depend on records (often spotty) of auroral activities and
of radioisotopes in ancient ice cores.
It
also raises the question of whether a "Maunder
Maximum" might be possible.
Left: As more than 300 years of
observations show, the "constant" sun has highly
variable. Links to 497x375-pixel,
66KB JPG. Credit: NASA/Marshall.
"If we look at other stars, you can
tell that they have sunspot cycles, too," Hathaway
replied. While features on the stars themselves cannot be
seen (except in a few cases), starspots can be tracked as
changes in emissions of ionized calcium.
Since 1966, Olin Wilson, Jr., at the Mt.
Wilson Observatory near Los Angeles has studied spots on
stars similar to our sun in age, size, and mass.
"You look at them and some aren't
having cycles at all, others match our sun, and others are
complete chaos," Hathaway said. "The sun
presumably does go through hyperactive phases at well."
But as with predicting CMEs, our level of understanding
isn't yet up to the task of predicting major changes in the
sunspot cycle, or even changes in the current cycle.
"I'm still sticking with what is our
best prediction and expecting a sunspot number of about 140
at maximum around mid-2000," Hathaway said. "I'm a
little worried about the prediction. But I see no reason to
throw it out. The sun is a variable object and there are
going to be some ups and downs."
Related Links:
The
Y2K Page
October 14: Solar
Cycle Update - Updated predictions from NASA
scientists place the solar maximum in mid-2000.
July 22: Seasons
of the Sun - Predicting what the Sun will do next.
April 13, 1998: New
sunspot cycle to be bigger than average, but no record
setter.
The
Sunspot Cycle - Information about the Sunspot Cycle
from the Marshall Solar Physics group.
Spaceweather.com
- daily updates on sunspot numbers and solar activity
December
16: Solar cycle ups and downs continues to mystify
scientists
December
15: The End of Days
December
15: Making up for Lost Leonids
December
14: Meet Conan the Bacterium
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