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| View Original: | Gibbous-Crescent-half-ellipse-in-circle.png (600x600) | |||
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| Keywords: Gibbous-Crescent-half-ellipse-in-circle.png Gibbous-Crescent-half-ellipse-in-circle svg A circle divided into a gibbous shape red and an astronomical crescent shape blue by a half-ellipse where the major axis of the ellipse coincides with a diameter of the circle According to geometry an illuminated hemisphere of a sphere will appear to take on such gibbous or crescent shapes when viewed from an angle In this case the length of the major axis of the ellipse is twice the length of the minor axis i e the eccentricity is half the square root of 3 so that the red gibbous area shows the theoretical shape of the visible lit area of the moon for example when the separation between the viewing angle and the angle of illumination i e between Earth and Sun is 60 degrees while the blue crescent area shows the theoretical shape of the visible lit area of a sphere when the separation between the viewing angle and the angle of illumination is 120 degrees See also Image Gibbous-Crescent-half-ellipse-in-circle-outlined png Generated by means of the following PostScript code <pre> 75 0 0 setrgbcolor 306 396 144 0 360 arc fill 0 2 85 setrgbcolor 306 396 144 90 -90 arcn 39 765 0 72 64 471 72 144 rcurveto 0 79 529 -32 235 144 -72 144 rcurveto closepath fill showpage EOF</pre> crescent shape Astronomy sketches Hemispheres Images with PostScript source code Blue and red | ||||
