Image credits: Historical reconstruction of yearly sunspot groups by D. V. Hoyt,
Research and Data Systems Corp., Yearly average sunspot
numbers from Zurich Observatory, Switzerland. Aurorae
data for the years 1780-present reconstructed
and compiled by J. P. Legrand, CNRS/INSU
(France), and by K. Krivsky, Astronomicky Ustav
(Czech Republic) for the years 1600-1720. |
- The first sunspots of the new cycle appear at 20 to 25 degrees latitude in both hemispheres. As the cycle continues, spots begin to appear at lower latitudes. As the end of the cycle approaches, the spots are concentrated near the equator. This pattern in the emergence of the sunspot when plotted against time produces the famous "butterfly" diagram
- Major solar cycle changes in the coronal structure can also be seen.
- A striking feature of this plot is the vastly reduced sunspot numbers in 1645-1715 called the Maunder minimum.
- Solar cycles are labeled from one minimum to the next. Solar cycle 1 was the 1755-1766 period. We are now in the ascending phase of solar cycle 23.
- The H alpha images are from the descending phase of solar cycle 21 and ascending phase of solar cycle 22. The minimum occurred in 1985-1986.
- The variation in the number of sunspots and their area coverage as well as in the appearance of plages and filaments is dramatic.
- The tendency for active regions to move towards the equator and to appear first at 30-40 degrees latitude is clear.
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