By June 29, 2011
What
a difference! These two images of the sun’s outer atmosphere, or
corona, were taken about 20 months apart. The sun is quiet in the
picture at left, taken in January 1997. In the picture at right, taken
in November 1998, the sun is more active.
When the sun’s activity
increases, more sunspots become visible. Credit: SOHO (ESA & NASA)
The sun is vital for life on Earth: It determines our calendars,
keeps us warm and delivers energy to plants. Not surprisingly,
scientists keep a close eye on the sun, looking for signs of change. If
the sun changes, there’s a good chance we’ll feel the effects on Earth.
The sun usually follows a pattern of activity that lasts 11 years.
This pattern is known as the solar cycle. Near the beginning of the
solar cycle, sunspots appear in increasing numbers near the poles.
Sunspots are dark dots that show up on the sun’s surface, and they are
caused by magnetic activity. (Don’t stand outside on a sunny day to look
for them: Staring directly at the sun causes permanent eye damage.)
Astronomers have been counting sunspots and tracking solar cycles for
400 years. For the most part, the sun has behaved according to the
11-year pattern. But recent studies of sunspots and other observations
of the sun suggest that the sun’s cycle may not be starting on schedule
this time.
“The next cycle may be very much more delayed, or may not happen at all,” Frank Hill told Science News.
Hill is a physicist at the National Solar Observatory in Tucson. Hill
and his colleagues recently studied the surface of the sun and didn’t
detect the telltale changes that happen at the start of a new solar
cycle.
The sun could be heading into hibernation, which means it will quiet
down for decades. It’s happened before: The last sun slowdown lasted
from 1645 until 1715. During those years, Europe experienced some of the
coldest winters on record.
The
clusters of sunspots at left may look tiny, but they’re the size of
Jupiter. At right, other sunspots are revealed in closeup. Credit: SOHO
(ESA & NASA)
If the sun is taking a break, physicists don’t know how our climate
might be affected this time. Earth’s atmosphere is very different than
it was 350 years ago. It now contains more greenhouse gases, like carbon
dioxide, that have been accumulating since the beginning of the
Industrial Revolution 200 years ago.
When fossil fuels like coal are burned, they release carbon dioxide
into the air. Those greenhouse gases insulate the Earth and trap heat.
As a result, temperatures are climbing. Physicists don’t know how an
insulated Earth will respond to decreased solar activity.
On the other hand, it’s possible that the sun isn’t headed into a
recess. The new sun cycle might just be running a few years, and not
decades, late. Dean Pesnell, a physicist at NASA’s Goddard Space Flight
Center in Greenbelt, Md., told Science News that the new studies indicate “that the next solar cycle will be delayed by two to five years,” or longer.
Three different teams of researchers presented studies about the
solar cycle at a June 14 meeting of sun scientists in Las Cruces, N.M.
In one study, Hill and his team looked for changes on the surface caused
by sound waves that bounce around the sun’s interior. In the past, this
type of study was able to predict the start of a solar cycle; this
time, the physicists didn’t see the signs of a start-up.
In the other two studies, scientists looked at the sun’s magnetic
fields. Magnetic activity drives the sun’s cycle, and those studies
showed that magnetic field activity right now isn’t strong enough to
jump-start a cycle. One of the studies shows that the magnetic field
actually has weakened over the past 13 years. In the near future, the
field may be too weak to form sunspots.
The trio of new studies suggests something strange is afoot in our
nearest star, although not everyone agrees the sun’s about to take a
long break. For scientists, a mystery or an unanswered question is
another chance to learn more about the universe and everything in it. As
Pesnell told Science News, “It’s a great time to be a solar physicist.”
POWER WORDS
solar Relating to the sun.
physics The scientific study of matter and energy.
sunspot A spot or patch appearing from time to time on the sun’s surface, appearing dark by contrast with its surroundings.
greenhouse gas A gas that contributes to the greenhouse effect by absorbing heat. Carbon dioxide is an example of a greenhouse gas
