Analemmatic sundials
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Stand on the name of the month and your shadow find out what time it is.
Analemmatic sundial consists of a dial and a scale of dates. The shape of dial is an ellipse, the ratio of the axes of which depends on the geographical coordinates.
In the polar latitudes, the shape of ellipse is close to a circle, whereas near the equator ellipse has an elongated shape. Minor axis of ellipse lies in the plane of local meridian. The major axis is directed from west to east. The scale of dates is orientated along the minor axis. A partition of the scale can be arbitrarily detailed, but usually the scale is parted according to the zodiac or calendar months.
The gnomon of analemmatic sundial is mobile. To determine the time the gnomon must be in the place of the scale of dates which corresponds to the day of observation. The direction of the shadow of the gnomon indicates the time. In the 17th — 18th centuries analemmatic sundials were small cabinet sized. Later, no one knows when, it came to someone to use a human body as a movable gnomon. If a person stands on the scale of dates on the place corresponding to the calendar date, he can find out what time it is by his own shadow.
In addition to time, with the help of analemmatic sundial is possible to determine the time of sunrise and sunset. It can be done even when the day is overcast and even at night. On the major axis of the ellipse the specific points can be located so that the line mentally drawn between these points and the day of observation on the scale points the time of sunrise and sunset on the dial.
The optimum size of an analemmatic sundial is 6 meters along the major axis.
Analematic sundial does not prevent the passage and travel, do not block adjacent urban landscape, it is very difficult to damage and it can not be stolen.