to the website of
The last solar eclipse
This page is temporarily 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famous scientists and historical documents.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
||Schmidt-Cassegrain telescope with F = 2030 mm, f/10
||Astrosolar density 5 with D = 72 mm (f/28)+ IR BG39
||Philips Vesta Pro Scan, mounted at the prime focus
|Image processing :
||IRIS 3.5.4 (freeware)
||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
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.
Pioneers in Solar Physics
(1611 - 1681)
(1642 - 1727)
Mass of the Sun
Joseph von Fraunhofer
(1789 - 1826)
Samuel H. Schwabe
(1789 - 1875)
(1816 - 1893)
Relative Sunspot Number
(1819 - 1868)
(1824 - 1887)
Chemical Composition of the Sun and spectral analysis
Samuel P. Langley
(1834 - 1906)
George Ellery Hale
(1868 - 1938)
Sun's Magnetic Cycle
(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
an index frame
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michelØwillemin.li (SPAM protection: replace Ø by @)