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Are you ready for the Partial Solar Eclipse on Oktober 25th, 2022?
Every now and then, the moon moves in front of the sun and we experience a solar eclipse. In Europe, we will have to wait until August 12th, 2026 for the next total solar eclipse. It will be visible as a total solar eclipse e.g. from Spain, while the sun will remain only partially eclipsed from Germany. Fortunately, we won't have to wait that long for the next partial solar eclipse: In the midday hours of October 25th this year, the moon will eclipse a third of the sun's disc. Observers in the north-east of the German-speaking region will have somewhat more of it than those in the south-west: on the island of Rügen, as much as 35% of the sun will be covered, in Switzerland only about 15%. At 82%, the greatest occultation will be seen from western Siberia. In contrast to a total solar eclipse, where everyone waits anxiously for few minutes of totality, a partial solar eclipse is a rather relaxed event - over the course of (this time) about two hours, you can watch the moon move along in front of the sun. First, as always, the warning: Never look directly into the sun without a...
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Tips for Choosing an Energy Rejection Filter for H-alpha-Observations
The purpose of an Energy Rejection Filter is to prevent as much solar energy as possible from entering the telescope in the first place and thus avoid excessive heating of the etalon of an H-alpha filter. This is done most effectively by a filter in front of the telescope. At the same time, this prevents the air in the tube from heating up - the telescope remains close to the ambient temperature, and there are no air turbulences inside of the OTA due to temperature differences. If we look at the solar spectrum, it becomes clear that such a filter must primarily block visible light. Ideally, it reflects the solar energy energy instead of absorbing it and and does not heat itself up in the process as well - that's why these filters are called Energy Rejection Filters (ERF for short). Since it is occasionally asked: A Herschel wedge or a white-light front-filter cannot be used as an ERF because it also darkens the H-alpha line. In H-alpha, the sun is far less bright than in white light, so there would be practically no light left to observe. There are usually three types of filters mentioned, when Energy Rejection...
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