Sunspot Archives

Today's sunspot
number is

Courtesy National Oceanic and Atmospheric Administration

What is the Sunspot Number?

For more information on current solar conditions visit
The Space Weather Bureau
Sunspot Plotter (Java support required)

The Java applet below allows you to plot 11 years worth of sunspot number centered on any date between 1755 and the present. Using the pull-down menus enter the date of interest, and hit "Refresh". Click here for a plot of all monthly-averaged sunspot numbers from the year 1749 through the present.

Greenwich Sunspot Data

See also: Monthly averages of sunspot numbers from 1749 through the present (updated monthly):
(25 kb GIF image)
(37 kb postscript file)
(62 kb text file)

What is the Sunspot Number? The Space Environment Services Center (SESC) sunspot number for the indicated date is from the daily Solar Region Summary issued by SESC. The SESC sunspot number is computed according to the Wolf Sunspot Number R=k (10g+s), where g is the number of sunspot groups (regions), s is the total number of individual spots in all the groups, and k is a variable scaling factor (usually <1) that indicates the combined effects of observing conditions, telescope, and bias of the solar observers. A sunspot number of zero indicates there were no visible sunspots on that date; a blank indicates that no observations were taken. The sunspot region information used to compute the daily sunspot number incorporates reports from as many as six observatories. These reports are used to form a composite picture of each individual region, including sunspot number, area and classification, taking into account such factors as the time of observation and the quality of seeing. This composite information is the daily average obtained from the reporting observatories and may not represent the latest data. It is reported daily in the Solar Region Summary and listed in the Region Summary section of the Weekly.

(Note: there are actually two "official" sunspot numbers reported. The International Sunspot Number is compiled by the Sunspot Index Data Center in Belgium. The NOAA, or American, sunspot number is compiled by the US National Oceanic and Atmospheric Administration.)

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