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Here we are proposing an astronomical analysis of the directions of the diagonal avenues of Washington, made by means of satellite images and a modern ephemeris, the Photographer s Ephemeris, a well-known software used for planning outdoor photography. The diagonal streets of Washington seem had been aligned along moonrise and moonset azimuths of 1791, the year the engineer Pierre Charles L Enfant planned the town for George Washington.
Astronomical Alignments of the Diagonal Avenues of Washington
Amelia Carolina Sparavigna
Politecnico di Torino
Abstract: Here we are proposing an astronomical analysis of the directions of the diagonal avenues of Washington, made by means of satellite images and a modern ephemeris, the Photographer s Ephemeris, a well-known software used for planning outdoor photography. The diagonal streets of Washington seem had been aligned along moonrise and moonset azimuths of 1791, the year the engineer Pierre Charles L'Enfant planned the town for George Washington.
Keywords: Astronomy, Satellite Images, Architecture, Modern Ephemerides
In this work we will show that the urban plan of Washington is containing a precise astronomical reference, which is linking the Capital to the year of foundation. This urban plan is known as the L'Enfant Plan. It was developed in 1791 by Major Pierre Charles L'Enfant for George Washington, the first President of the United States.
Major L'Enfant was a French engineer who served in the American Revolutionary War. In Wikipedia , we can find the detailed story of the plan. Shortly: in 1789, L'Enfant wrote to President Washington asking to be commissioned for the planning of the Capital. However, any decision was put on hold until July 1790, when Congress passed the Residence Act. This Act gave authority to Washington to appoint three commissioners to oversee the land surveying. Then in 1791 L'Enfant was appointed to design the new capital city under the supervision of the three commissioners.
L'Enfant arrived in Georgetown on March 1791 and began his work, then Washington arrived to meet with L'Enfant and the Commissioners for several days. Then, President Washington retained one of L'Enfant's plans, showing it to Congress. L'Enfant's "Plan of the city intended for the permanent seat of the government of the United States…" encompassed an area bounded by the Potomac River, the Eastern Branch, the base of the escarpment of the Atlantic Seaboard Fall Line, and Rock Creek" .
A note important for our astronomical analysis is given in the item of Wikipedia. We can read that L'Enfant's plan contained the following explanatory note: "In order to execute the above plan, Mr. Ellicott drew a true meridian line by celestial observation, which passes through the area intended for the Congress-House; this line he crossed by another line due east and west and which passes through the same area. These lines were accurately measured, and made the basis on which the whole plan was executed. He ran all the lines by a transit instrument, and determined the acute angles by actual measurement, and left nothing to the uncertainty of the compass". It is clear then the importance the celestial observations had for L’Enfant.
By means of the satellite images, it is easy to see the streets that are making a chessboard of parallel and perpendicular streets, like the ancient Roman towns that were planned with the Centuriation . We see the North-South streets which are aligned along the “Axis Mundi”, the axis about which the sky seems rotating. We have also the East-West streets aligned along sunrise and sunset azimuths on equinoxes. But there are also the diagonal avenues. These avenues were later named after the states of the union crossed the grid. As explained by Wikipedia, “the diagonal avenues intersected with the north-south and east-west streets at circles and rectangular plazas that would later honor notable Americans and provide open space”.
Let us make an astronomical analysis of the directions of the diagonal avenues by means of satellite images and a modern ephemeris, the Photographer s Ephemeris, a well-known software used for planning outdoor photography. We have used this method for the streets of Turin for instance .
As we can see by the snapshots of the Photographer’s Ephemeris outputs in the Figures 1-3, the diagonal streets of Washington seem had been aligned along moonrise and moonset azimuths of a minor lunar standstill (October 2015).
In 1791, the year the engineer Pierre Charles L'Enfant planned the town for George Washington, we were quite close to a minor lunar standstill, as we can see from the web page astropixels.com/ephemeris/moon/moondecmax1701.html. At this site we can find the list of the Greatest Annual Lunar Standstills: 1701 to 1800. For 1791, the minimum declination was on Jan 03 of -19.161, the maximum on Jan 17 of 19.107. For 1792 (minor lunar standstill), the minimum declination was on Dec 14 of -18.569, the maximum on Dec 27 of 18.587. For 1793, on Dec 05 we had -19.272 and on Dec 18 of 19.306. Algorithms used are based on Astronomical Algorithms by Jean Meeus (Willmann-Bell, 1998; the table of the Greatest Annual Lunar Standstills is a courtesy of Fred Espenak, www.Astropixels.com).
The difference of declination and then of azimuth between 1791 and 1792 is small. The same happens if we consider years 2014, 2015 and 2016; it is difficult to appreciate any difference by the Photographer’s Ephemeris if we consider the moon azimuths on October of these years. In fact, after the astronomical analysis, we can conclude the following. In his planning, it is quite probable that Pierre Charles L'Enfant aligned the diagonal avenues of Washington along moonrise and moonset azimuths of 1791, the year he planned the town for George Washington. Then, in the planning of the Capital of the United States, there is also a reference to the year of the foundation.
 Vv. Aa. (2016). L’Enfant Plan, Wikipedia.
 Sparavigna, A. C. (2015). Roman Centuriation in Satellite Images. PHILICA Article number 547. Available at SSRN: http://ssrn.com/abstract=2742223
 Sparavigna, A. C. (2016). The Orientation of a Street of Turin along the Major Southern Moonrise Direction. SSRN Journal. DOI: 10.2139/ssrn.2779906
Figure 1: Snapshot of the Photographer’s Ephemeris for Washington on October 3, 2015. The blue lines are the moonrise and moonset azimuths, the yellow and orange lines those of sunrise and sunset. Note the coincidence to the diagonal avenues.
Figure 2: Snapshot of the Photographer’s Ephemeris for Washington on October 3, 2015.
Figure 3: Snapshot of the Photographer’s Ephemeris for Washington on October 18, 2015.
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Sparavigna, A. (2016). Astronomical Alignments of the Diagonal Avenues of Washington. PHILICA.COM Article number 612.