A simple lens focuses the Sun onto an occulting disk that prevents the light from the solar disk from proceeding farther along the optical path, effectively providing an artificial eclipse.Īn extended region of the corona, exceptionally low in density and associated with unipolar photospheric regions having ”open” magnetic field topology. In spectroscopy, and in particular the solar Fraunhofer spectrum, a characteristic wavelength of emitted radiation that is partially absorbed by the medium between the source and the observer.Ī descriptive word specifically meaning (1) a probability of ~50% for an M- class x-ray flare (see x-ray flare class) (2) disturbed geomagnetic levels such that 16 10 6 K).Īn optical device that makes it possible to observe the corona at times other than during an eclipse.
The index is available back to 1868, and is provided by the Institut du Globe de Paris, France. A daily and half-daily index of geomagnetic activity determined from the k indices scaled at two nearly antipodal stations at invariant magnetic latitude 50 degrees (Hartland, England, and Canberra, Australia).
