Range of radio electromagnetic waves with frequencies between 300 MHz and 3 GHz.

Radiation of immediately shorter wavelengths than visible light, between 5 and 400 nm. Extreme ultraviolet (EUV) and x-rays have shorter wavelengths yet.

The central umbra, which is the darkest part of a sunspot, where the magnetic field is approximately vertical (normal to the sun's surface).

Time referred to the zero meridian of longitude (through Greenwich, UK). 0000 UT is local midnight at Greenwich. For example, 12 UT equal to 09 BRT .

Airglow images corrected to geographical coordinates system.

The largest decile, one of nine, that has 90% of the ordered values below it.

This is a statistical prediction of the highest frequency for HF sky wave propagation. If the prediction is correct, this frequency should be refracted by the ionosphere 10% of the time. See Maximum Usable Frequency and Optimum Working Frequency.

The region lying nearer the Sun than the Earth, where the solar wind has yet to encounter (is upstream from) the Earth