Author: Todd Arend Date posted: Aug 24, 2009 Article views: 75 Wordcount: 525 Re-Publish
Sundials are an ancient method for telling time. Sundial time is actually more accurate than clock time, according to some people, since sundials give solar time, which is based on the position of the sun in your exact location.
However, everything is not based on solar time, but on clock time. So, if you want to figure out the exact time from your sundial, the Planetary Society has suggested three adjustments to make to the time reading from your sundial.
First, you should adjust the reading for your location within your time zone. In example, if you live on the western edge of your time zone, your sundial will read about thirty minutes slow, while sundials on the eastern edge will read about thirty minutes faster than clock time.
The basic rule for adjusting within your time zone is that for every degree of longitude west of the center of the time zone your sundial is located you should add four minutes from the time your sundial reading. If you live east of your time zone center, subtract four minutes for each degree. This conversion will allow you to adjust solar time in your exact location to the actual clock time.
It is also essential to take daylight savings time into consideration. During the summer months, you should add one hour to your sundial reading to find the actual time you will find on your clock.
The last conversion you should make is the most complicated and confusing. Clock time was designed to proceed in complete regularity; each day, hour, and second is exactly the same length of time as the next. However, this consistency does not exist in solar time.
Over one year, the time from one solar noon to the next averages out to be exactly twenty-four hours; however on any given day it can be up to thirty seconds longer or shorter. This discrepancy is due to the 23.4 degree tilt of the Earth's axis and the slight non-circularity of the Earth's orbit. The result of these factors is that the time on your sundial can differ up to fifteen minutes from clock time, even at the center of the time zone.
This modification is known as the Equation of Time. This name is based on an archaic meaning of the word equation, which refers to equating one time system to another. You can look up the amount of time you need to add or subtract to the time you read on your dial for each day of the year online.
If you make these three adjustments, you will be able to read the exact clock time from your sundial. However, most people do not think it is worth the effort to know the exact time, so they either allow their sundial to only be a decoration, or they just use it to read an approximate time.
No matter how important the accuracy of your time reading is to you, a sundial is a striking addition to your backyard or garden. They come in many different styles and are made of different materials that will suit any sort of aesthetic taste.
Todd Arend is a freelance writing professional whose expertise covers a variety of areas, including patio and backyard furniture, landscaping and design. He regularly writes about sundials and patio heaters.
