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 4

When speaking of circles or parts of a circle, we refer to them in degrees, a complete circle containing 36o degrees (360°), each degree containing 6o minutes (6o'), and each minute containing 6o seconds (6o"). The degree constitutes the unit of circular measure. If we divide the celestial equator, which is nothing but a complete circle, into 24 equal parts, each part will contain 15 degrees. Therefore i hour which is 1/24 part of a circle; will be equal to 15 degrees. In the construction of a sundial we assume that the sun is situated on the celestial equator, which is the enlargement of our earthly equator until it touches the sky. It is also assumed that the sun stays in that position throughout the year, marking out equal spaces throughout the day and night equivalent to our twenty-four hours, which is explained in more detail in Section Six. From our geography we know that the equator lies at right angles to the axis of the earth, or the polar axis as it is called. Since the earth's polar axis if extended in either direction would pass through the celestial poles, it follows that the celestial equator lies at right angles to the polar axis of the celestial globe or sphere.

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