Balázs Kretzer

TL;DR: The sky-polarimetric Viking navigation based on Haidinger's brushes is most useful after sunset and prior to sunrise, when the sun is not visible and large sky regions are bright, clear and polarized enough for perception of Haidingen's brushes.

TL;DR: It is shown that real calcite crystals are not as ideal sunstones as it was believed earlier, because they usually contain scratches, impurities and crystal defects which increase considerably their adjustment errors, and cordierite and tourmaline can also be at least as good sunstone as calcite.

TL;DR: According to the findings, the ideal periods for sky-polarimetric Viking navigation are immediately after sunrise and before sunset, because the North errors are the lowest at low solar elevations.

TL;DR: The meteorological conditions under which Vikings could have used this hypothetical sky-polarimetric Viking navigation method are revealed and the solar elevations at which the navigation uncertainties are minimal at summer solstice and spring equinox for all three sunstone types are determined.

TL;DR: The software package used to process and evaluate the morphology of lightnings obtained that test persons can estimate the number of lightning branches quite correctly if Nb ≤ 11, which explains why artists usually illustrate lightnings with branches not larger than 11.