SUNDIAL SECTIONS:

Sundials Home

History of Sundials

Why the Sun Dial keeps time

Developing and Making Sundials

Sundial Materials

Sundial Hour Lines Lay out

Sundial "Furniture"

Declination Lines of Sundials

Portable Sundials

Interesting Sundials of the World

WHY THE SUNDIAL KEEPS TIME - Page 5

We learn one more thing from observation and geography, that the north star, so-called because it is the star nearest the north celestial pole, is not right over head, nor on the horizon, unless we are situated at the north pole of the earth, or on the equator. We further know that this angle of elevation of the celestial pole above the horizon will be equal to the latitude of whatever place we may be in when we observe it. This is also true for the south celestial pole. That the shadow casting edge of any sundial must always point to the celestial pole, and makes an angle with a level line equal to the latitude of the place for which the sundial is made and in which it is to be used, together with the assumption that the sun is on the equator throughout the year, are the two facts upon which the construction of all sundials is based. This leads directly to one more fact that the twelve o'clock line always lies in a true north-south direction whether on a vertical, horizontal, or any other type of sundial, because the sun would always be on the north line of any locality at twelve o'clock noon, by sun time. Therefore with these facts at hand it is possible to plot the position and direction of a shadow, cast on any surface in any position. Thus we produce a surface marked out in such a manner that it will record equal hours which may be observed and read by the position of a shadow. A surface so marked is called a sundial, and would serve our purpose admirably if we did not have clocks and watches.

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