The Dolphin Sundial
Designed by Christopher St. J. H. Daniel;
bronze sculpture by Edwin Russell FRBS

The gnomon, or pointer, of the sundial is formed by the tips of the two dolphins’ tails, which almost meet. The tails cast a shadow onto the dial plate, which is engraved with thick curved lines representing the hours. Thinner lines indicate 10-minute intervals between each hour.

The dial plate has curved lines, rather than straight ones, to allow for the variations in the Sun’s apparent daily motion. The plate used in summer shows British Summer Time; that used in winter shows Greenwich Mean Time.

The mid-point between the shadows of the dolphins’ tail-tips indicates the correct time.

Example (not to scale)
Time indicated:
[Illustration]

The Dolphin Sundial was commissioned by theNational Maritime Museum in 1977 to commemorate the Silver Jubilee of Her Majesty Queen Elizabeth II

It was unveiled on 5 June 1978 by the Baroness Birk, in the main grounds of the Museum. It was moved here in June 2009 during the re-landscaping of this garden, which was made possible by the generosity of the Friends of the National Maritime Museum.

The Sundial is in the Meridian Garden, a place where various historical measuring and observation instruments are concentrated.

The sundial which is actually also a sculpture was made by the artist Edwin Russell.

The sundial was taken on the same day Click for a larger image Click for a larger image

Next to the sign, there is another sign explaining the differences between clock time and sundial time
Sundials and solar time
Clock time and sundial time often appear different. Clock time is based on the assumption that each day lasts for exactly 24 hours all through the year. In contrast, sundial time accounts for seasonal variations in day length caused by the Earth’s tilted axis and its elliptical orbit around the Sun.

When these two effects are combined, we produce the wavy pattern seen in the accompanying figure, known as the Equation of Time. When the curve is below the horizontal axis, noon on a sundial occurs several minutes after noon on a clock during these months. When the curve is above the horizontal axis, noon on a sundial occurs several minutes before noon on a clock.

The maximum difference between local solar time and mean (clock) time is 16 minutes and this occurs on 4 November. There are four days in the year when sundials and clocks coincide at noon: 16 April, 15 June, 1 September and 25 December.

[figure]
Sundial and clock time are the same when the curve crosses the horizontal axis.
Click for a larger image