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Longitudinal Correction

Our sundial can be designed to show the clock time (LMT) or it can be designed to show Local Apparent Time (LAT)

The sundials below are designed for clock time or Local Mean Time. (LMT)


Note 1:

This dimension is determined by how far away the sundial is from the standard meridian  which is the longitude that everybody within that time zone sets their clock to. Whether it’s rotated clockwise or counter-clockwise will depend if the sundial is east or west from the  Standard Meridian. In this case, it’s 75 degrees longitude. To design a sundial to show LAT, this angle is zero as in the sundial shown below.

Note 2:

This dimension is determined by the latitude that the sundial is designed for. The closer the sundial is to the equator, the smaller this dimension will be.

The people that live at Atlanta and Lincoln both set their clock as if they live on the same longitude. Eastern Standard Time is based on 75 degrees longitude

A sundial designed with longitude correction will only work for that particular latitude and longitude.

The sundial above is designed for Local Apparent Time. As with all sundials, it can be constructed only on the latitude that it was designed for. However, it can be placed on ANY longitude. Note that 12 noon is on the top and isn’t rotated either right or left.

Solar time is very different to clock time. When it’s 12 noon at Lincoln Maine, it’s 11:24 at Atlanta Georgia.

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