- The current sunspot cycle is expected
to intensify and could have important consequences for Earth, according
to scientists at NASA's Marshall Space Flight Center.
- Every 11 years the sun undergoes a period
of activity called the "solar maximum," followed by a period
of quiet called the "solar minimum." During the solar maximum
there are many sunspots, solar flares, and coronal mass ejections, all
of which can affect communications, disrupt power systems and alter weather
here on Earth.
- "The consensus [among solar physicists]
is that this cycle will be above average in size and probably a fast riser,"
NASA's Robert M. Wilson says.
- "It's like saying we're going to
have a mild or cold winter," says Dr. David Hathaway of Marshall Space
Flight Center. "We're in a similar state in predicting what the sun's
climate is going to do."
- The Earth is affected by both solar flares
and sunspots. Solar flares emit high-speed particles which cause auroras,
known in the northern hemisphere as Northern Lights.
- Particles from solar flares can also
disrupt radio communication, and the radiation from the flares can give
passengers in airplanes a dose of radiation equivalent to a medical X-ray.
- We even have tantalizing hints that the
Earth's climate may be linked to sunspots.
- The "Little Ice Age" corresponded
with a 70-year period, 1645-1715, when sunspots were sparse in number.
- Still, with almost 250 years of observations
- of which only the last 150 years are considered truly reliable- predictions
are akin to the Farmer's Almanac, Hathaway says.
- "There's no real physics involved,"
he explains. "It's all statistical inferences."
- The sun now is on the upswing of its
23rd activity cycle, a numbering scheme that dates from the mid 19th century,
following introduction of the "relative sunspot number" by Rudolf
Wolf of the Zurich Observatory in 1848.
- On average, this number varies from a
minimum through a maximum to the next minimum in about 11 years. Because
the solar magnetic fields reverse at the peak of each 11-year cycle, solar
activity cycle actually spans a 22-year "Hale cycle." Cycle 23
is the last half of the current Hale cycle that began in 1986.
- Scientists simply count the number of
sunspots, and when the numbrs increase, they know the sun is headed for
another solar maximum.
- Another way is by means of the "Butterfly
Diagram." At the beginning of a new sunspot cycle sunspots appear
mainly at high solar latitudes, close to the Sun's north and south poles.
As the sunspot cycle progresses, sunspots appear closer to the Sun's equator.
By plotting the latitudes of sunspots throughout the solar cycle a plot
diagram that literally resembles a butterfly pattern appears.
- The relatively early appearance of sunspots
at mid-solar latitudes has many solar physicists predicting an unusually
large sunspot maximum in the year 2001.
- Based on various techniques, Hathaway,
Wilson, and Reichmann predict that Cycle 23 will rise faster than normal
to its peak, attaining maximum amplitude sometime during the latter half
of 1999 to the first half of 2000. They expect Cycle 23 to continue until
sometime in 2006 when the next cycle, Cycle 24, should begin.