Posted on 10/24/2003 9:54:17 AM PDT by Mike Darancette
THE SUNSPOT CYCLE
Marshall Space Flight Center http://science.msfc.nasa.gov/ssl/pad/solar/sunspots.htm
Sunspot Numbers
In 1610, shortly after viewing the sun with his new telescope, Galileo Galilei made the first European observations of Sunspots. Daily observations were started at the Zurich Observatory in 1749 and with the addition of other observatories continuous observations were obtained starting in 1849. The sunspot number is calculated by first counting the number of sunspot groups and then the number of individual sunspots. The "sunspot number" is then given by the sum of the number of individual sunspots and ten times the number of groups. Since most sunspot groups have, on average, about ten spots, this formula for counting sunspots gives reliable numbers even when the observing conditions are less than ideal and small spots are hard to see. Monthly averages (updated monthly) of the sunspot numbers (25 kb GIF image), (37 kb postscript file), (62 kb text file) show that the number of sunspots visible on the sun waxes and wanes with an approximate 11-year cycle.
(Note: there are actually at least two "official" sunspot numbers reported. The International Sunspot Number is compiled by the Sunspot Index Data Center in Belgium. The NOAA sunspot number is compiled by the US National Oceanic and Atmospheric Administration (. The numbers tabulated in spot_num.txt are the monthly averages (SSN) and standard deviation (DEV) derived from the International Sunspot Numbers)
The Maunder Minimum
Early records of sunspots indicate that the Sun went through a period of inactivity in the late 17th century. Very few sunspots were seen on the Sun from about 1645 to 1715 (38 kb JPEG image). Although the observations were not as extensive as in later years, the Sun was in fact well observed during this time and this lack of sunspots is well documented. This period of solar inactivity also corresponds to a climatic period called the "Little Ice Age" when rivers that are normally ice-free froze and snow fields remained year-round at lower altitudes. There is evidence that the Sun has had similar periods of inactivity in the more distant past. The connection between solar activity and terrestrial climate is an area of on-going research.
The Butterfly Diagram
Detailed observations of sunspots have been obtained by the Royal Greenwich Observatory since 1874. These observations include information on the sizes and positions of sunspots as well as their numbers. These data show that sunspots do not appear at random over the surface of the sun but are concentrated in two latitude bands on either side of the equator. A butterfly diagram (142 kb GIF image) (610 kb postscript file) (updated monthly) showing the positions of the spots for each rotation of the sun since May 1874 shows that these bands first form at mid-latitudes, widen, and then move toward the equator as each cycle progresses. The cycles overlap at the time of sunspot cycle minimum with old cycle spots near the equator and new cycle spots at high latitudes. An alternate version of this diagram with different colors for even and odd numbered cycles is available as a 610kb postscript file.
The Greenwich Sunspot Data
The Royal Greenwich Observatory data has been appended with data obtained by the US Air Force Solar Optical Observing Network since 1976. This newer data has been reformatted to conform to the older Greenwich data and both are available in a local directory of ASCII files. Each file contains records for a given year with individual records providing information on the daily observations of active regions.
Sunspot Cycle Predictions
MSFC Solar Physics Branch members Wilson, Hathaway, and Reichmann have studied the sunspot record for characteristic behavior that might help in predicting future sunspot activity. Our current predictions of solar activity for the next few years can be found at this link. Although sunspots themselves produce only minor effects on solar emissions, the magnetic activity that accompanies the sunspots can produce dramatic changes in the ultraviolet and soft x-ray emission levels. These changes over the solar cycle have important consequences for the Earth's upper atmosphere.
Sunspot 10486 may prove to be more interesting. It has already kicked out a couple of X class flares, including one beaut above X5, and is moving toward the position from which it could launch a CME toward us.
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THE SUNSPOT CYCLE
Posted by Mike Darancette
On 10/24/2003 9:54 AM PDT with 7 comments
Marshall Space Flight Center ^ | 10/23/03 | Marshall Space Flight Center
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