...Is because it's the one the Founders planned.
http://ericfrancis.com/issues/0307/full-moon.html In 1690, the Chapter of Perfection, an esoteric astrological community in Germantown, Pennsylvania (now part of northwest Philadelphia) was founded by John Kelpius.
Grounded in the work of European Rosicrucians and Freemasons, the group was an offshoot of a secret order in London called the Masonic Rite of Perfection, which involved John Jacob Zimmerman and Jane (Ward) Lead, former members of the original Philadelphians, a mystic cult inspired by Jakob Boehme in Germany.
Franklin, Thomas Jefferson and George Washington were all influenced by those same esoteric astrologers.
"Much of their work centered on selecting the 'best times, ideas, designs of seals and monuments, to initiate activities that would lead to the creation of a nation powerful enough to withstand the attempts of Britain, the world superpower, to regain its prized colonies'. Egyptian magic is evident." ("Washington D.C.'s Astrological Secrets").
David Ovason, author of The Secret Architecture of Our Nation's Capital (Harper Collins), says Washington D.C. is unique; much of the city's original design is firmly grounded in astrology. The planners followed ancient Greek and Egyptian mysteries by aligning the city with a constellation's fixed stars, he says. His book focuses on the 1791 planning of the city's Federal Triangle (the Washington Monument, White House and Capitol building) and the alignment with the three main stars of the constellation Virgo.
In Dell Horoscopes' "Ben Franklin: America's Astrologer-General," Lina Accurso writes:
"Only in books on astrology and its history are you apt to discover
Benjamin Franklin and Thomas Jefferson (another all-around philosophical and scientific genius) conspired to have the Declaration of Independence adopted on July 4, 1776, rather than on July 2, the date urged by in-a-hurry John Adams. July 2, the Moon was in one of its weakest signs, Capricorn, where it would oppose the Cancer Sun, Mercury, Venus and Jupiter. By July 4, the full Moon was safely into Aquarius and well out of opposition to the Sun. Coincidence, historians would scoff. Smart logical planning...
"One of the few 'civilian' books to mention Franklin and astrology on the same page is an old one, Franklin, The Apostle of Modern Times, by Bernard Fay (Little Brown, 1929) To quote him at some length: "Astrology was very much in vogue...It occupied an important place in business, agriculture and private life. Astrology was employed in determining the future of newly born children. The date to choose for a hunt, the propitious period for sowing seed and gathering grapes, the opportune moment for the departure of boats...Wise, serious, and pious people also believed in astrology, for as late as 1728 candidates for Harvard discussed such topics as these: 'Do medical herbs operate by planetary power?' or 'That the heavenly bodies produce changes in the bodies of animals.' And on the eve of the Revolution in 1777, the faculty proposed such subjects as these: 'Is a comet which only appears after many years a foreshadowing of divine wrath rather than a planet that appears daily?'
"Everybody turned to the astrologers, and the publishers of almanacs had an immense public. These little books were the faithful mirrors of the preoccupations of the times."