Zenithal

He improved the methods of astronomical measurement, invented the zenithal collimator, suggested and applied photography and electricity to astronomy, and dealt with problems of physical astronomy, the shape of comets, the spots of the sun, meteors, etc. ❋ 1840-1916 (1913)

Its transcendental aspirations -- still unconsciously based on the geocentric view of things, a zenithal paradise, a nadiral hell -- were as foreign to his own as if they had been the dreams of people on another planet. ❋ Unknown (1891)

A thick fog came down on us, with zenithal aurora borealis, the electric action of which threw out every compass, standard and otherwise, on board. ❋ Prince De Joinville (1859)

However they represent extreme solar UV exposure conditions with a quasi zenithal sun irradiance i.e. a UVA to UVB irradiance ratio of less than 18, representative of a high UVB level. ❋ Claire Marionnet Et Al. (2010)

To assess more realistic solar UV exposure, a non-zenithal UV spectrum has been defined as standard daily ultraviolet radiation (DUVR) spectrum, with a UVA to UVB irradiance ratio of around 27 ❋ Claire Marionnet Et Al. (2010)

However, they addressed the worst case scenario i.e. zenithal sun, rarely found in common outdoor activities. ❋ Claire Marionnet Et Al. (2010)

Therefore zenithal sun exposure conditions, corresponding to summer sunlight at noon and maximizing UVB proportion are rarely found. ❋ Claire Marionnet Et Al. (2010)