Half-arc angle: Difference between revisions
From Glossary of Meteorology
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<div class="definition"><div class="short_definition">The [[elevation angle]] of that point that a given observer regards as the bisector of the arc from his [[zenith]] to his [[horizon]]; a measure of the apparent degree of flattening of the dome of the sky.</div><br/> <div class="paragraph">Because to almost all persons the sky appears not as a hemispheric dome but rather as a more oblate surface, the half-arc angle designated by most observers is substantially less than 45& | <div class="definition"><div class="short_definition">The [[elevation angle]] of that point that a given observer regards as the bisector of the arc from his [[zenith]] to his [[horizon]]; a measure of the apparent degree of flattening of the dome of the sky.</div><br/> <div class="paragraph">Because to almost all persons the sky appears not as a hemispheric dome but rather as a more oblate surface, the half-arc angle designated by most observers is substantially less than 45°, usually falling within the interval 20°–35°. The more remote the landmarks on an observer 's horizon, the smaller in general will be his designated value of the half-arc angle. Also, presence of a [[cloud]] deck serves to produce an apparent flattening effect. No fully satisfactory explanation exists to account for the apparent flattening of the sky.</div><br/> </div> | ||
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Latest revision as of 14:22, 20 February 2012
half-arc angle
The elevation angle of that point that a given observer regards as the bisector of the arc from his zenith to his horizon; a measure of the apparent degree of flattening of the dome of the sky.
Because to almost all persons the sky appears not as a hemispheric dome but rather as a more oblate surface, the half-arc angle designated by most observers is substantially less than 45°, usually falling within the interval 20°–35°. The more remote the landmarks on an observer 's horizon, the smaller in general will be his designated value of the half-arc angle. Also, presence of a cloud deck serves to produce an apparent flattening effect. No fully satisfactory explanation exists to account for the apparent flattening of the sky.
