Sundials - World's Oldest Clocks

North American Sundial Society

This Sundials for Starters appeared in The Compendium in March, 2006

by Robert L. Kellogg, Ph.D

I usually get up at 7am (ante meridian), but unlike ancient farmers, the time of rise has almost nothing to do with sunrise. One June 21st, and just west of Washington D.C. my sunrise occurs at 5:43 am Eastern Daylight Time (EDT). That would be 4:43 am Eastern Standard Time (EST) if we left our clocks alone. I’m almost due west of Washington D.C. and the Ellipse in front of the White House. Interestinglyu, my sunrise will occur about 44 seconds after sunlight rises on the White House.  How does this relate to longitude?

Here’s the math:

Thanks to Google Earth, I’ve found out that my house (actually, my mail box) is located at 38º 59’ 35.90” north latitude and 77º 13’ 9.72”west longitude. The center of the Ellipse is located at 77º 2’ 11.51”west longitude. That’s a difference of 10’ 58.21” or 0.1828 º. In terms of measuring time:

360 degrees of longitude = 24 hours of time

1 degree of longitude = 24*60/360 = 4 minutes of time = 240 seconds

So I live 0.1828 x 240 = 43.87 seconds west of the White House

We recognize the convention of time zones using the meridian of Greenwich, England as the 0º reference. The attempt is to divide the world into 15º strips of longitude where everyone in the zone has the same time. If you look at a map of the world’s time zones, you realize that this goal is only partially accomplished, since the real time zones must allow for political boundaries and preferences for common trade to alter the pure 15º mathematical abstraction. Figure 1 shows how the world is really divided:

Figure 1 World Time Zones

The Eastern Time zone of the United States is centered on 75º longitude west of Greenwich. But we did not always use Greenwich. As history books remind us, Pierre Charles L’Enfant was asked by President Washington to be architect of Washington, D.C. In L’Enfant’s 1791 street plan Congress House (now the Capitol) was designated to be 0º 0’ 0” longitude for the new country. What is not commonly remembered is that L'Enfant was later dismissed from the project and when he left, he took the city plans with him.

Fortunately in 1791, Benjamin Banneker, a self-taught astronomer and competitor to Benjamin Franklin’s Poor Richard’s Almanac, became one of three surveyors appointed by President George Washington to help survey the "Federal Territory" of Washington, D.C. When L’Enfant left, Banneker recreated the city plans in two days, including a complete layout of the streets, parks, and major buildings. The city of Washington, D.C. itself is a tribute to Banneker's memory.

But the Capitol’s prime meridian was short lived. In 1793 Thomas Jefferson surveyed a marker for the U.S. prime meridian west of the Capitol and during his presidency in 1804 placed a granite block on the site, which by today’s reference is about 119 meters west-north-west of the Washington Monument on the Mall. Today a tourist can go to 38º 53’ 23”.29 north latitude and 77º 02’ 15”.34 west longitude and find in the shadow of the Washington Monument a smaller monument stating “Position of Jefferson Pier Erected Dec. 18, 1804 Recovered and Re-Erected Dec. 2, 1889”.

But Jefferson envisioned a loftier place for marking the American Meridian and designated an area about 1.5 miles north of the White House on a line with 16th street as the spot for the meridian, marking the spot with a small obelisk in 1804. The obelisk is gone, but the name “Meridian Hill” still remains as the name of the area near 16th street and Florida Avenue N.W in Washington D.C.

Now the U.S. meridian was on the move. Appropriated in 1849 and approved in 1850 Congress declared that the [old] Naval Observatory overlooking the Anacostia River on 24th Street in the District of Columbia should be adopted as the American Meridian. The official location of the observatory’s dome was declared as being 5 hrs 8 min 12.15 sec west of Greenwich. Using the same math from the beginning of this column, but recognizing that one hour of time is 15 degrees of longitude, the American Meridian was declared as 77º 03’ 2”.25. This meridian was used to define the boundaries of Kansas and Colorado in 1861, separated North Dakota from Montana in 1889, set the border of Wyoming to 27º west, separated Utah and Nevada at 36º west, and divided Arizona and New Mexico at 32º west.

In 1884 twenty five nations convened in Washington, D.C. to attend the International Meridian Conference. Since the majority of navigation charts already used Greenwich as reference, there was nearly unanimous vote for Greenwich as the prime meridian. However there was dissent from France and Algeria, both abstaining. The Algerian diplomat made the disparaging comment that Greenwich Time should be called “Paris Mean Time Diminished by 9 minutes 21 seconds.” And truth be known it would take the U.S. Congress until 22 August 1912 to finally repeal the official use of the American meridian and adopt the Greenwich reference.

References:

www.math.nus.edu/aslaksen/projects/sundials

http://aa.usno.navy.mil/data/docs/RS_OneDay.html

http://aa.usno.navy.mil/faq/docs/world_tzones.html

http://ngx.noaa.gov/INFO/Washmon/info.htm