The Henry Moore Sundial Sculpture
Adler Planetarium & Astronomy Museum, Chicago, IL
41.8°N latitude, 87.6°W longitude
This type of sundial is a variety of the classic equatorial sundial, often referred to
as a "bowstring equatorial sundial" (similar to the "bow" in "bow &
arrow"). The dial
plate (representing the equatorial
plane) has been reduced to a semi-circular band representing
approximately one-half of the Earth's Equator,
referred to as the "equatorial band." The equatorial band serves as the
"time scale." The gnomon
(or style)
is a thin rod (the "bowstring") representing the Earth's axis of
rotation.
The vertically-oriented "bow" represents a single
meridian (line of longitude) and is referred to as the "meridian band."
The bow is connected to the bowstring at the equivalent of the Earth's
North and South Poles. The bow is attached to a pedestal or "foot."
The hour
lines for the bowstring equatorial sundial are laid out on the inner
surface of the equatorial band. Every hour is 1/24 of a day, or exactly 15
degrees wide. The shadow of the gnomon (or style), cast among the hour lines on the
equatorial band, shows the time. The 12 o'clock noon hour line
intersects the "bow" or meridian band (unless the sundial has been
corrected for the longitudinal offset from the Standard Time Meridian).
Morning times are located on the left side of the equatorial band;
afternoon times are on the right.
The primary advantage of this type of equatorial sundial is that the style
shadow is cast upon a single time scale all year long
(regardless of whether the Sun is north or south of the Celestial
Equator), and unlike classic equatorial sundials, should work on the
day of the equinoxes
(although the author has not witnessed this firsthand).
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