Monday 20 April 2015


There are some large sunspots visible at the moment, and on Saturday the weather was – for a brief moment – good enough to get the camera and solar filter out (see warning below!), which we used during the live webcast of the recent solar eclipse, and take some photos! The sunspots are clearly visible, click the photo for a full-resolution version.

Zooming in, one can clearly distinguish the darker umbra from the lighter penumbra around the sunspot. Sunspots are caused by strong magnetic fields on the surface of the Sun, and they are cooler than the rest of the solar surface, and thus they appear darker.

The peculiar shaded areas on the solar surface in the photo above are very thin clouds at the location of observation. Clouds coming and going rapidly made focussing particularly difficult.

Warning: Do not look at the Sun without special protecting solar folio or eclipse glasses! If you intend to use welding goggles, make sure they are at least factor 14 or darker (according to recommendation of the URSA Astronomical Association), and even with these glasses, one should not look at the Sun continuously for more than a few minutes! Standard welding glasses are typically 9 to 11 darkness, which is not enough! The sunlight can destroy your eyes, and you won't notice it at the time of observation, but only afterwards.

Photo (800mm, f/11, 1/125s) by Thomas Ulich.

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