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Here we are proposing an astronomical analysis of the directions of some 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. Some diagonal streets of Washington seem had been aligned along the northern moonrise azimuth of 1791, the year the engineer Pierre Charles L Enfant started the survey for planning the town for George Washington, and along the southern moonrise azimuths of 1792, the year the surveyor Andrew Ellicott revised the plan. In this manner, in the directions of some diagonal avenues, the engineers that worked on the urban project, introduced a reference to the years of their plans for the Capital of the United States.
An Astronomical Analysis of Some of the Diagonal Avenues of Washington
Amelia Carolina Sparavigna
Politecnico di Torino
Abstract: Here we are proposing an astronomical analysis of the directions of some 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. Some diagonal streets of Washington seem had been aligned along the northern moonrise azimuth of 1791, the year the engineer Pierre Charles L Enfant started the survey for planning the town for George Washington, and along the southern moonrise azimuths of 1792, the year the surveyor Andrew Ellicott revised the plan. In this manner, in the directions of some diagonal avenues, the engineers that worked on the urban project, introduced a reference to the years of their plans for the Capital of the United States.
Keywords: Astronomy, Satellite Images, Architecture, Modern Ephemerides
In this work we will show that the urban plan of Washington is containing precise astronomical references, which are linking the Capital to the years of its planning. Its urban plan started as a project which is known as L'Enfant Plan. It was developed in 1791 by Major Pierre Charles L'Enfant for George Washington, the first President of the United States. The plan was revised and completed in 1792 by Andrew Ellicott, an U.S. surveyor. 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 of Washington D.C. 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 these three persons.
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 the Congress. This was the plan of the city that encompassed an area bounded by the Potomac River, the Eastern Branch, the base of the escarpment of the Atlantic Seaboard Fall Line, and the 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 from this note the importance the celestial observations had for L’Enfant and for Ellicott in the surveying works.
The above-mentioned note is on L’Enfant plan of the city of which an annotated facsimile was created by the U.S. Coast and Geodetic Survey, Washington, in 1887. This copy is in the Library of Congress. It is given in the Figure 1. In the Figure 2, we can see a detail of this plan and some angles formed by the diagonal avenues. In the Figure 3, we give a detail of the original map of 1791, that we can find at the Library of Congress too, https://www.loc.gov/item/88694205/. To see the streets it is necessary to apply a digital image processing.
Figure 1 – Copy of the U.S. Coast and Geodetic Survey, Washington, D.C. (1887).
Figure 2 – Detail of Figure 1, with some diagonal avenues of L’Enfant Plan and angles.
Figure 3 – A detail of the faint original map of 1791 (https://www.loc.gov/item/88694205/) after a processing of the image.
Let us compare the Figures 2 and 3 with the satellite images of the same part of Washington. By means of these images, it is easy to see that, as in L’Enfant plan, the streets are making a chessboard of parallel and perpendicular streets, like it happened for the ancient Roman towns that were planned with a centuriation . We see, from the map of Figure 4, that the town has the North-South streets perfectly aligned along the cardinal direction, the “axis mundi”, that is, the axis about which the world is rotating. We have also the East-West streets aligned along sunrise and sunset azimuths on equinoxes. But there are also the diagonal avenues, the avenues that were later named after the states of the union, and that are crossing 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”.
Figure 4 – Google map of Washington.
Note that we have some differences when this map is compared to Figures 2 and 3. In particular, we see that the angles of 18 and 17 degrees turned into angles of 24 degrees.
There is a reason. As explained in , during a contentious period in February 1792, Andrew Ellicott, who had been conducting the original surveying under the direction of the Commissioners, informed them that L'Enfant had not been able to have the city plan engraved and had refused to provide him with the original plan. Ellicott, with the aid of his brother Benjamin, revised the plan, despite L'Enfant's protests. Shortly thereafter, Washington dismissed L'Enfant. After L'Enfant departed, Andrew Ellicott continued the surveying in accordance to his revised plan.
In fact, if we compare Figures 2, 3 and 4, we have to note that Ellicott maintained the angle of 24 degrees of the diagonal avenues, even rendering the plan more symmetric. It means then that this angle had probably a specific meaning.
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 and for the Decumani of Napoli [3,4]. As we can see by the snapshots of the Photographer s Ephemeris outputs in the Figures 5-7, the diagonal streets of Washington seem had been aligned along moonrise and moonset azimuths of a minor lunar standstill (October 2015). In the Figures 5 and 6, it is shown the northern moonrise and moonset azimuths the moon can have in this period. In the Figure 7, we can see the southern moonrise and moonset azimuths, the moon is reaching during the minor lunar standstill.
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 that was in 1792, 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, from 1701 to 1800. For 1791, the minimum declination was of -19,161 on January 03, the maximum declination was of 19.107 on January 17. For 1792, the minor lunar standstill, the minimum declination was of -18.569, December 14, and the maximum of 18.587, December 27. For 1793, on December 05 we had a minimum declination of -19.272 and, on December 18, a maximum of 19.306. Algorithms used are based on Astronomical Algorithms by Jean Meeus (Willmann-Bell, 1998; the data 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 observe the moon azimuths for these years.
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 northern moonrise azimuths of 1791, the year he planned the town. Then, in the following year, 1792, the year of a minor lunar standstill, Ellicott that was probably well aware of this astronomical situation, reinforced the astronomical alignment adding the symmetry of angles, and then the alignment along southern moonrise azimuths. Then, in the directions of some diagonal avenues of the Capital of the United States, we can find also a reference to the years of its planning, through the alignments along moonrise and moonset azimuths.
 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). Alignments of the Streets of Torino with Moonrise and Moonset Azimuths on Major and Minor Lunar Standstills. SSRN DOI: 10.2139/ssrn.2782566
 Sparavigna, Amelia Carolina, The Decumani of Naples and the Minor Lunar Standstill (May 29, 2016). PHILICA, Article number 608. Available at SSRN: http://ssrn.com/abstract=2786259
Figure 5: 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 6: Snapshot of the Photographer s Ephemeris for Washington on October 3, 2015.
Figure 7: Snapshot of the Photographer s Ephemeris for Washington on October 18, 2015.
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Sparavigna, A. (2016). An Astronomical Analysis of Some of the Diagonal Avenues of Washington. PHILICA.COM Article number 613.