Purtroppo, questa descrizione non è stato tradotto in italiano, in modo da trovare a questo punto una descrizione inglese.
One of the most important obstacles for the exploration of the night sky is the brightening of the night sky by artificial lights, such as streetlights. The night sky is not really dark in the vicinity of towns or cities, which reduces the visibility of objects beyond the Solar System enourmously.
Depending on the type of celestial object, it is possible to increase the contrast dramatically by blocking the annoying artifical light. The H-Beta filter uses a characteristic property of the so called emmission nebulae. Those objekcts glow in special colors, the emmission lines. These emmission lines are linked to chemical elements - in this case hydrogen. A H-Beta nebula filter blocks all other colors (and thereby nearly all of the artificial light) and only the emmission line of the hydrogen can pass the filter. The result is astonishing: Suddenly nebulae are visible at locations that were completely empty without a filter. In suburban skies for example the Horsehead Nebula is almost invisible with a 300mm telescope. By using this filter you can see the nebula and its structures without any problems. A must-have for every visual observer!
