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The Sun
The Latest Solar Maximum

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Solar maximum is the two-to-three year period around the peak of activity when the Sun appears most tempestuous and Earth is buffeted with powerful solar gusts.    [solar cycle years]

The latest sunspot cycle is number 23. Solar scientists have calculated that the Sun reached the solar maximum of the latest eleven-year sunspot activity cycle in the month of April 2000 when the smoothed sunspot number (SSN) was 120.8.    [smoothed sunspot number]

Is it like Cycle 20? Solar astronomers have suggested that Cycle 23 is much like Cycle 20 in the way it rose and fell. Cycle 20 took about four years to reach peak and about seven uears to descend to minimum. If the two are alike, that could mean that Cycle 23 would reach bottom in 2007. The peak of Cycle 24 then might come in 2011.

Magnetic flip. An additional indication that Cycle 23 peaked in the year 2000 came in a NASA report in February 2001 that the Sun's magnetic field had flipped. That means that Sun's north pole, which had been in the northern hemisphere of the Sun before the flip, now is in the southern hemisphere.The flip really wasn't a surprise since it seems to happen at the peak of each solar cycle.

Twin Peaks? However, solar scientists noticed in 2002 what some called an odd second peak in the solar cycle. Was activity on the Sun increasing again? Sunspots peppered the star's surface.

The latest solar cycle appears to be double-peaked, according to a solar physicist at NASA's Marshall Space Flight Center, who finds solar activity chaotic. Other astronomers checked back on past eleven-year cycles and discovered that Cycle 23 may have peaked a few months earlier than might have been expected. Was that a sign of a second maximum to come?

Early Warning? The apparent resurgence was a full two years after the Sun had been seen to reach Cycle 23 solar maximum. To solar astronomers, such a second peak of activity was unusual, but not unprecedented. Cycle 22 looked much the same. Its first peak arrived in mid-1989 followed by a smaller maximum in early 1991. In fact, Cycle 23 now may be the third double-peaked cycle in a row. Is nature changing or are humans just better able to discover it?

Layers of the Sun. The Sun varies during its solar cycle because of action in a turbulent outer layer of our star. The outermost third is a convective zone with gas rising and falling in bubbles as big as a planet. A radiative zone underneath the convective zone is calmer. From there, photons carry the Sun's energy upward and outward.

Strong electric currents flow at the boundary between the convective zone and the radiative zone, and the Sun's magnetic field is generated there.    [NASA diagram of the Sun]

In 2001, scientists used a technique known as helioseismology to peer into the interior of the Sun. There they found gas currents at the base of the convective zone that changed velocity every 16 months. Interestingly, that was about the same length of time as the period between the double peaks during recent solar maxima. It wasn't clear whether there was a connection.

During a solar maximum, the intense magnetic fields that shoot far above the Sun's surface become tangled, particularly in regions of the solar surface near sunspots. Those twisted magnetic fields can fall back down suddenly, causing them to explode into powerful solar flares and coronal mass ejections (CMEs).    [definitions of Sun terms]

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