Since ages we try to figure out about the Sun. Every day we are wondering if it's going to be sunny or rainy. Other people are breaking their heads about her behaviour, her appearance, her structure, her influence on us,... Satellites are watching and listening to the Sun for 24 hours a day, every day of the year. But has it ever occurred to you that the Sun possibly has a secret private life and that she is preparing for Valentine, February 14?
The picture above is taken by the Solar X-ray Imager, simply SXI, on the earth-orbiting satellite GOES-12. From the whole radiation spectrum emitted by the Sun, it filters X-rays. These are energetic rays, with short wavelengths and high frequencies. In the picture are parts of the Sun emitting strongly in that particular wavelength brighter than other parts.
On board of the satellite is also an instrument measuring the overall x-ray radiation and gives you an x-ray plot as shown in the picture below. With overall we mean that all the x-ray radiation coming from the global solar disk on a specific time is counted. A flare is an instantaneous and local strong enhancement of x-ray radiation seen as a peak on top of the background radiation curve. It is possible on a SXI image of that moment for example, to locate the active region responsible for the flare: the region will look much brighter than others.
