The
Geochron, perhaps best described as a functional wall sculpture, is a dramatic
2-foot-by-3-foot (34 1/4" x 22 1/2" x 4 1/2") global
map/chronometer, framed with wood and encased behind glass, whose timepiece is
synchronized with the earth's orbit. The
principal objective of the Geochron is to provide a device capable of
pictorializing, on a flat surface global solar time and its modifications as
well as related natural phenomena. The Geochron
displays the following: Legal
Zone Time, Greenwich mean time, Greenwich apparent time, local apparent time,
local mean time, moment of sunrise, moment of sunset, duration of daylight,
sun's meridian passage, sun's equation of time, degrees latitude, degrees
longitude, the geographic extent of the prevailing day and date.
A Brief
Introduction to Solar Time, Its Modifications, and Related Facts The
basis of daily time measurement is the relationship of the earth's surface to
the sun. Thus, when the earth makes one revolution about its axis relative
to the sun, it is said to be one day. However, the speed of the earth's
travel around the sun varies so that over a period of one year, some days are
shorter and others longer, causing the relative zenith, or noon position of the
sun to vary accordingly. This is what is measured by a sun
dial-"apparent solar time". For time
measurement purposes, man has taken the "mean" between the longest and
the shortest apparent solar days, divided it into 24 equal hours, and thus had
"mean solar time". When our clocks say 12 o'clock "mean
time", it does not necessarily indicate that the sun is at its zenith.
For the largest part of the year, there is a difference between "mean
noon" and " apparent noon", and this difference is called the
"equation of time". One's location
in longitude within a time zone also affects the relationship between
"apparent noon" and "legal zone time noon". the
geographic extent of a given day is determined by the position of the
international dateline (180 degrees meridian of longitude) relative the
"mean sun" or "mean noon". For example, if the
international dateline coincides with the "mean sun" (mean noon), half
of the earth's surface is today and the other half is tomorrow or yesterday,
depending on which half one's position is. thus, there are two
different week days and dates at any given moment, except for an instant each
day when it is midnight at the dateline. At this point of time, the same
day exists around the earth. "Zone
time" is, of course, the designated time for a given area measuring,
ideally, 15 degrees in longitude, having a standard meridian central to the
zone. In practice, however, legal zone boundaries are highly irregular and
non-conforming. Further distortion of "ideal" zone time occurs where
daylight savings time is used. The time of
sunrise and sunset is influenced by one's position in latitude, due to the 23
1/2 degrees tilt of the earth relative to its orbital plane. It also
varies due to the changing speed of the earth along its orbit around the sun.
For example, at the equator, the time of sunrise and sunset varies 30 minutes
over a period of one year, (same as equation of time) while the actual
daylight period remains nearly constant. Design
Consideration of the Geochron The
information shown by Geochron is displayed on a flat surface rather than a globe
because only a limited legible area is seen when glancing at a globe.
The instrument is normally hung from the wall. To permit recess
mounting, its depth is based on the 3- 1/2" width of a standard wall stud.
Thus, Geochron can be surface or flush mounted. Both methods are also
designed to prevent accidental dropping of the instrument.
The length and height of the Geochron are governed by the fact that one inch of
longitude on the map is equal to one hour, and that 75 degrees north latitude
and 66 1/2 degrees south latitude cover all areas of time telling importance.
Geochron's appearance is intended to be simple, devoid of apparent controls and
knobs, and its finish is adaptable to prevailing decor.
The fluorescent tubes, starters and ballasts used in its internal illumination
are accessible and replaceable without dismantling the unit. | 
The Summer Solstice
The Winter Solstice
The Spring and Autumn Equinoxes!
