Calgary Board of Education

Environmental Learning

Native Plant Park

Recycling | Composting | Enviro Club | Curriculum Integration | Phases | Plants | Do's and Don'ts | History of Environmental Activities


Map of Phase III

Map of Phase III
The Human Sundial
Info Centre
Phase I & II
Phase III

Equation of Time

When comparing sundial time to clock time, the times will be exactly the same on some days of the year, but on the other dates they will differ slightly. Why? Standardized clock time is based on the premise that the earth rotates once (360 degrees) every 24 hours, every day of the year. Yet this is not true. As the earth orbits the sun, it varies slightly in its speed and its path. These slight variations result in some days being fractionally longer than 24 hours, and some shorter, althought we standardize our clocks so that each day is exactly 24 hours long. The difference between standardized clock time and sundial time is called The Equation of Time. At certain times of the year, sundial time may differ from clock time by up to 20 minutes. At other times of the year, when the Equation of Time is zero, sundial time and clock time will be the same. To find out the value of the Equation of Time for any particular day, again access the website SunAngle, type in the particulars, and out will pop the Equation of Time correction!

Details of the Analemmatic Sundial

Installing an Analemmatic Sundial

Equation of Time