Sunspots represent magnetic activity on the surface and interior of the sun and have a cycle that averages 11 years. The 2008 minimum was the lowest in a century.

As a result, solar flares were almost nonexistent, and solar extreme ultraviolet radiation was at low ebb.

When solar extreme ultraviolet activity is low, it causes the thermosphere of Earth's atmosphere to shrink, and the contraction that took place in 2008-09 was the greatest in nearly 50 years.

Due to decreased atmospheric drag, the shrinking thermosphere changed the orbits of satellites.

During the same interval, the solar wind pressure was the weakest in 50 years, following a decreasing trend that began in the 1990s.

The solar wind permeates the entire solar system and creates the heliosphere, a bubble of magnetism originating from the sun and inflated by the solar wind. The entire solar system is inside the magnetic bubble. It is the first line of defense against cosmic rays.

In 2009 cosmic rays increased 19 percent over the highest seen in the past 50 years. The atmosphere protects us, but the increase created a danger for astronauts and satellites.

A whole fleet of spacecraft is devoted to solar physics. Monitoring the sun's vibrating surface allows helioseismologists to probe the stellar interior.

An article published in Nature yesterday revealed a new computer model of the sun's interior showing that plasma currents deep inside the sun interfered with the formation of sunspots and prolonged the solar minimum.

Like Earth, the sun has surface currents that run from the equator to the poles, then plunge deep beneath the surface and travel back to the poles.

These currents drag decaying sunspots below the surface where its magnetic dynamo amplifies their decaying magnetic fields. Reanimated sunspots become buoyant and bob up to the surface to begin a new solar cycle.

In the 1990s, the solar conveyor sped up so that when the sunspots reached the amplification zone, they moved too quickly to be fully reanimated, thus stunting sunspot activity.

When the conveyor slowed in the early 2000s, new sunspots were in short supply, delaying the onset of the next sunspot cycle.

"Understanding and predicting solar minimum is something we've never been able to do before, and it turns out to be very important," said Lika Guhathakurta of NASA's Heliophysics Division in Washington, D.C.

While solar maxima are relatively brief, lasting a few years, solar minima can grind on for many years.

The famous Maunder Minimum of the 17th century lasted 70 years and coincided with the deepest part of Europe's Little Ice Age.

Using helioseismography, NASA's Solar Dynamics Observatory can measure the motions of the sun's conveyor belt on the surface and deep inside.

By plugging the observatory's data into this new computer model, the researchers might be able to predict how future solar activity will unfold.

Richard Brill is a professor of science at Honolulu Community College. E-mail questions and comments to rickb@hcc.hawaii.edu.