Solar activity during the year 2002

This page is devoted to the impressive solar activity during the year 2002. According to the eleven-year cycle, 2002 is very close to the maximum. All images presented on this site have been taken by the authors, excepted the portraits of famous scientists and historical documents. Most of the images have required telescopes and special filters! Never look directly at the Sun with the naked eye or with any optical instrument without reducing light intensity. Eye and instrument damages may result.

Image of a huge sunspot group, which is much larger than the diameter of the earth. Sunspots are active regions in the solar photosphere which have reduced temperatures compared with their surrounding, making them appear dark. Large spots have usually a dark interior, the umbra, surrounded, or at least partly so, by a lighter area known as the penumbra. Both area are clearly visible on this image. © M. Willemin

Experimental setup

Instrumentation : Schmidt-Cassegrain telescope with F = 2030 mm, f/10
Filters : Astrosolar density 5 with D = 72 mm (f/28)+ IR BG39
Camera : Philips Vesta Pro Scan, mounted at the prime focus
Image processing : IRIS 3.5.4 (freeware)
Time : August 17, 2002, from Lignières (Switzerland), © M.W.

Solar Activity - Wolf Number

The relative sunspot number (Wolf number) is an index of the activity of the entire visible disk of the Sun. It is determined each day without reference to preceding days. Each isolated cluster of sunspots is termed a sunspot group, and it may consist of one or a large number of distinct spots whose size can range from 10 or more square degrees of the solar surface down to the limit of resolution (e.g., 1/25 square degree). The relative sunspot number is defined as R = K (10g + s), where g is the number of sunspot groups and s is the total number of distinct spots. The scale factor K (usually less than unity) depends on the observer and is intended to effect the conversion to the scale originated by Wolf.

The eleven-year cycle of the solar activity is clearly visible on this graph. The exact date of the maximum of a cycle is very difficult to determine. As an example, the maximum of the last cycle (cycle 23) occurred between 2000 and 2001. (Source for relative sunspot numbers: NGDC/NOAA)

As mentioned previously, the solar activity during the year 2002 was still very high. The sunspot group from the photograph displayed above was taken on August 17, 2002 (see the violet point with a Wolf Number of 186), precisely at a relative maximum! The contribution of this group for the Wolf number was clearly dominating.


Never view the Sun through optical instruments like telescopes or binoculars without reducing light intensity with appropriate filters. Irreversible eye damage may result!

Pioneers in Solar Physics

Johannes Hevelius
(1611 - 1681)
Sunspot Observation

Isaac Newton
(1642 - 1727)
Mass of the Sun

Joseph von Fraunhofer
(1789 - 1826)
Spectral Measurements

Samuel H. Schwabe
(1789 - 1875)
Sunspot Cycle

Rudolf Wolf
(1816 - 1893)
Relative Sunspot Number

Léon Foucault
(1819 - 1868)
Sun Photography

Gustav Kirchhoff
(1824 - 1887)
Chemical Composition of the Sun and spectral analysis

Samuel P. Langley
(1834 - 1906)
Solar Constant

George Ellery Hale
(1868 - 1938)
Sun's Magnetic Cycle

Bernard Lyot
(1897 - 1952)

This historical document gives only a brief overview of famous scientists, who gave an important contribution to the knowledge of the sun. This list cannot be exhaustive within the frame of such a website. The omission of important personalities is clearly not related to a minor or negligible contribution.

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