Solar activity during March 2001

(very close to the maximum of the cycle 23)


This page describes the impressive solar activity observed during the second part of March 2001. The huge sunspot group photographed below was still visible after two complete rotations of the Sun.


Instrumentation : Newton telescope with F = 445 mm, f/6
Sun filter : Astrosolar foil (density 5), opt. diam. 72 mm, f/d = 6.2
Additional filter : IR rejection filter BG39 (Schott)
Camera : Philips Vesta Pro Scan, mounted at the prime focus
Exposure : 1/1500 s
Time : March 31, 2001, 11H27 (UT), from Affoltern am Albis (Switzerland), © M. Willemin
Instrumentation : Achromat refractor with F = 910 mm, f/11
Sun filter : Astrosolar foil (density 5), opt. diam. 72 mm, f/d = 12.6
Additional filter : IR rejection filter BG39 (Schott)
Camera : Philips Vesta Pro Scan, mounted at the prime focus
Exposure : 1/500 s
Time : March 31, 2001, 11H52 (UT), from Affoltern am Albis (Switzerland), © M. Willemin

No correction of the type offset (subtraction of flat field), gain, contrast, intensity, and sharpness has been used for the image processing of these two imagess. The raw images are in the VGA format (640 x 480), on an 8 bits greyscale. The color has been introduced by modifying the weight of the three RGB channels.

The sunspot number or Wolf number, determined by SOHO, was 325 on March 31 2001 at 01H36 UT. This is one of the highest values observed during the cycle 23. The maximum has been reached two days before. Unfortunately, the weather in Switzerland was not optimal at this date. During the sunset and when the atmospheric absorption is high enough, the large sunspot group is visible by naked eye.

The biggest sunspots versus time


Sun filter used for solar photography (see images on the top) and for visual observation. It can be mounted either on a small refractor or on the mini Newton telescope (F = 445 mm, f/6). The filter frame is made of oxidized aluminium, which allows an ideal mounting of an Astrosolar foil (density 5). The foil should be as flat as possible and any mechanical stress would deteriorates the image quality.

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