Term Equatorial sundial can refer to any device that uses the Sun's altitude or azimuth to show the time.
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20 Facts About Equatorial sundial
2.
The reading of an old Equatorial sundial should be corrected by applying the present-day equation of time, not one from the period when the dial was made.
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3.
Heliochronometer is a precision Equatorial sundial first devised in about 1763 by Philipp Hahn and improved by Abbe Guyoux in about 1827.
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4.
The world's largest axial gnomon Equatorial sundial is the mast of the Sundial Bridge at Turtle Bay in Redding, California.
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5.
The hour-lines on the Equatorial sundial are marked to show the positions of the shadow of the style when this clock shows whole numbers of hours, and are labelled with these numbers of hours.
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6.
An ancient variant of the equatorial sundial has only a nodus and the concentric circular hour-lines are arranged to resemble a spider-web.
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7.
When L equals 90°, the horizontal sundial becomes an equatorial sundial; the style points straight up, and the horizontal plane is aligned with the equatorial plane; the hour-line formula becomes = 15° × t, as for an equatorial dial.
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8.
Chief advantages of the horizontal Equatorial sundial are that it is easy to read, and the sunlight lights the face throughout the year.
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9.
Since the style is aligned with the Earth's rotational axis, the style points true North and its angle with the horizontal equals the sundial's geographical latitude L A sundial designed for one latitude can be adjusted for use at another latitude by tilting its base upwards or downwards by an angle equal to the difference in latitude.
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10.
For example, a Equatorial sundial designed for a latitude of 40° can be used at a latitude of 45°, if the Equatorial sundial plane is tilted upwards by 5°, thus aligning the style with the Earth's rotational axis.
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11.
Where is the Equatorial sundial's geographical latitude; t is the time before or after noon; is the angle of declination from true south, defined as positive when east of south; and is a switch integer for the dial orientation.
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12.
Such a Equatorial sundial might be located on a South-facing roof, for example.
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13.
The hour-lines for such a Equatorial sundial can be calculated by slightly correcting the horizontal formula above.
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14.
For example, such a Equatorial sundial might be found on a roof that was not oriented in a cardinal direction.
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15.
An equivalent type of Equatorial sundial using a vertical rod of fixed length is known as a backstaff dial.
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16.
The entire Equatorial sundial is then twisted on its string so that the gnomon aims toward the Sun, while the cylinder remains vertical.
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17.
Digital Equatorial sundial indicates the current time with numerals formed by the sunlight striking it.
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18.
The typical noon-mark Equatorial sundial was a lens set above an analemmatic plate.
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19.
Conversely, if the directions of the cardinal points are initially unknown, but the Equatorial sundial is aligned so it shows the correct apparent solar time as calculated from the reading of a clock, its gnomon shows the direction of True North or South, allowing the Equatorial sundial to be used as a compass.
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20.
The Equatorial sundial can be placed on a horizontal surface, and rotated about a vertical axis until it shows the correct time.
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