We live in a constantly changing world, but each day, one thing remains the same: The sun rises in the east and sets in the west - although not in exactly the same spot on the horizon.
Summer holds the longest day of the year, when the sun rises and falls to the extreme north end of east and west, tracing a high arc in the sky.
The sun seems to stand still briefly, then, almost undetectably, it begins creeping farther and farther south, until reaching the shortest day of the year about Dec. 21, when the winter solstice sun rises and sets farthest south, staying low in the sky.
Sundials have marked those daylight hours for thousands of years, casting shadows that moved to tell the time as the sun's position changed relative to the Earth. They take on many forms: flat horizontal or vertical dial plates with numbered faces, spherical armillary globes and other irregular shapes. A raised bar called a gnomon is angled up from the face to cast a shadow on the dial.
Sundials range from a plain stick in the ground to elaborate works of art and complex, finely calibrated structures. A sundial can create a sculptural focus for garden settings.
They can be found all over the world, sometimes in unexpected places.
In France, the spire of Mont St. Michel cathedral on a small coastal island casts a shadow more than a half-mile long at times, reaching numerals in the surrounding sands and water. At the National Maritime Museum in Greenwich, England, dolphin tails point to the hours, and a fine collection of pocket sundials, used before mechanical watches were invented, can be found in the historical collection.
If you're thinking of setting up your own garden sundial, remember that you need to have one with a gnomon fixed at an angle approximately equal to your latitude.
You should position the gnomon's high point toward true north, which is currently about 5 degrees to the right of magnetic north on a compass. You also could simply point it at the North Star. During the year, magnetic north shifts a bit, but you can check the adjustment by plugging in your ZIP code at the Web site ngdc.noaa.gov/geomagmodels/Declination.jsp.
Remember also to place your sundial in a spot where sunlight can shine on it directly for most of the day.
To learn more, and to take a look at a mind-boggling number of sundials, go to the North American Sundial Society's Web site, sundials.org.