Solar activity has been very low over the last weeks, with very few or no C-class flares at all. The x-ray background flux was also low, at or just below the B1 level. Around noon on 5 April, this background flux started a gentle increase to values slightly above B3 on 7 April, coinciding with the appearance of a big sunspot near the solar east limb.
The new region quickly got the number NOAA 2529. It was a bipolar sunspot group with a big, symmetric main spot and a surface area 5 to 6 times the total surface area of the Earth. Several solar observers, using protective eclipse glasses, reported the sunspot group as a naked eye object on 10 April. Consistent with its rather simple magnetic configuration, the region produced only some low-level C-class flares. Interestingly, this flaring activity was already observed while the region was still behind the solar limb. In the end, the region produced all 16 C-class flares of last week, including two long duration events on 9 April (C2.8 flare) and 10 April (C1.5 flare), but no M-class flares (so far).
The clips of the related movie all cover the period from noon on 5 April till noon on 9 April. SDO imagery is used, and the clips were created using the JHelioviewer software ). The first clip shows a full solar disk in white light and extreme ultraviolet (AIA131; blue, several million degrees). It is followed by a zoom in the same wavelengths. The next two clips show the same zoomed comparison to white light, but in wavelengths of successively lower temperatures, resp. AIA171 (green, +/- 700.000 degrees) and AIA304 (red, +/- 80.000 degrees). The next two clips show the four wavelengths at the same time, resp. as separate images (see image above) and overlaid one onto the other (see below for a 90 degrees rotated image). Most of the activity was coming from the trailing part of the region.
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