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A Fairfax County Public Schools Planetarium
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No. 1 1/2-size | full-size | info Side view, facing east. |
An equatorial sundial is actually a reduced model of the Earth, similar to a globe with its upper and lower halves removed: the dial plate represents the plane of the Earth's Equator; the gnomon represents the Earth's axis of rotation. The upper dial face represents the Northern Hemisphere; the lower dial face represents the Southern Hemisphere. The unique design of the Webster Park equatorial sundial enables the user to concretely visualize this abstraction. | ||
No. 2 1/2-size | full-size | info Upper dial face. |
No. 3 1/2-size | full-size | info Closer view. |
No. 4 1/2-size | full-size | info Close-up view. |
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No. 5 1/2-size | full-size | info Lower dial face. |
No. 6 1/2-size | full-size | info Facing west-northwest. |
No. 7 1/2-size | full-size | info Facing east-northeast. |
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No. 8 1/2-size | full-size | info Close-up, Earth globe (showing part of Eastern Hemisphere). |
No. 9 1/2-size | full-size | info Time marked on dial plate; date marked along gnomon. |
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No. 10 1/2-size | full-size | info December Solstice. |
Due to the geometry of equatorial sundials, the gnomon shadow is the same length for the entire day, although its length varies from day-to-day according to the annual cycle of change in the declination of the Sun. If the gnomon is sufficiently long, then its shadow falls beyond the edge of the dial plate (see photo No. 10, shown left). In that case, the date may be determined by marking the position of the shadow of the dial plate that falls along the gnomon: dates between the SEP- and MAR Equinoxes are marked along the segment of the gnomon that extends above the dial plate (see No. 9, shown above, & No. 11-13, shown below); dates between the MAR- and SEP Equinoxes are marked along the segment of the gnomon below the dial plate (see No. 1 & No. 5). | ||
No. 11 1/2-size | full-size | info Note shadow along gnomon. |
No. 12 1/2-size | full-size | info Closer view. |
No. 13 1/2-size | full-size | info Close-up, DEC 20 date marker. |
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No. 14 1/2-size | full-size | info From conceptual model... |
No. 15 1/2-size | full-size | info ...to dedication ceremony. |
No. 16 1/2-size | full-size | info Commemorative plaque. |
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Related Resources
Photographs courtesy Chuck Nafziger, Member, North American Sundial Society. Thumbnail images prepared using photoweb v3.0 by Phil Wherry & Eric Johnston. Me and My Shadow - Making the Sun-Earth Connection | SCSA Home |
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