3.3 EUV and visible light

At lower levels of the solar atmosphere, EUV emission lines allow a view on a region called flare transition layer that is also heated up quite abruptly (see example in Figure 1Watch/download Movie). From the upper chromosphere we receive the strongest signal in the Lyman-alpha line (at 121.6 nm) and the other members of the Lyman series of hydrogen. Lower down in the solar atmosphere, line emission from the Balmer series of hydrogen becomes dominant, with its most prominent member, the famous H-alpha line at 656.3 nm. In fact, most flare observations have been made using this line, since it is situated near the peak of the visible part of the solar spectrum and is thus easily accessible to ground-based observers. That is the reason why for many years the area at the time of maximum H-alpha brightness of flares and also their “importance” (faint, normal or brilliant) have been used for flare classification. Many volumes of Solar and Geophysical Data beginning in 1938 (published by NOAA) are filled with these data, and yet these lists are incomplete and suffer from non-objective judgments of different observers. A typical H-alpha flare observed from the ground is shown in Figure 13Watch/download Movie.UpdateJump To The Next Update Information

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Figure 13: mpg-Movie (312 KB) The flare on June 7, 2000, 1526 – 1621 UT, as seen by the H-alpha telescope (HASTA) in El Leoncito, Argentina External Linkhttp://www.oafa.fcefn.unsj-cuim.edu.ar/hasta/.

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