hebig.org/blog

The recent Venus transit has been a key event in astronomy, and of course a plethora of Sun/Venus-photos is available. The Venus part of most of them isn't too interesting to the bare eye, as the planet basically appears as a black circle. Perfectly visible to the bare eye: the fascinatingly low level of solar activity. Barely any solar spots, solar flares or flare loops. Among other things, solar activity directly affects radio communication on a number of important frequency bands: the level of solar activity influences how different layers of the earth's ionosphere build up, which in turn directly influences the lowest and highest usable frequency of specific bands. It follows an cycle with approx. 11 years peak-to-peak-time, and cleary, we are now seeing the end of cycle 23, as also indicated by current space weather reports: during Venus transit, a sunspot number - the key measurand of solar activity - of just 60 has been reported. Yesterday, it has been down to 37.2 which is one of the lowest number I've seen since I started to keep an eye on it 15 years ago. During a "good" peak, SSN can be as high as 250.

View complete image in full size >