Time > Reading a sundial

Reading time on a sundialReading the time on a sundial is really quite easy. In bright sunshine the gnomon on the sundial casts a clear shadow, which shows the time. Only the idea of using the sun to find the time is unfamiliar nowadays.

The shadow slips past each of the hour lines rather like a clock hand. It starts in the morning, goes past 12 noon in the middle of the day, and continues in the afternoon. The diagram shows the time at a quarter to two. Some sundials divide up the time between the hours but not this one.

Sundials are made so their time is correct by the sun. This is called solar time and is a local time. Clock time is different and it can be confusing to check a sundial and clock together. It depends on the place and the time of year. The times on a sundial and clock can be half an hour or more different even though both are correct.

Sundials are not affected by changing the clocks. When clocks are put forward during the summer, reading a sundial stays the same—the position of the sun in the sky has not changed. British Summer Time (BST) is one hour ahead of GMT.

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