The Royal Observatory
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royaL OBSERVATORY Mistresses, Meridians, Longitude & tiMe roceeding south on King William Walk, your through early spring gardens. These same paths were once path is blocked by the gold trimmed St. Mary’s trodden by the footsteps of Edmond Halley (the comet), Gate. To the east is a landscaped promenade fea- Charles Mason (and Dixon), Isaac Newton (falling apples), turing prominently a ship in the bottle, perhaps Christopher Wren (St. Paul’s Cathedral) and any number of ten feet in diameter and twenty-five in length. To surveyors and astronomers and Kings and Queens of the realm. the west is the Greenwich Tavern “The Mature The entire “astronomick” enterprise was begun long Neighbourly Gastric Pub, Please Enjoy Responsibly and before the fabled sinking of the Shovell fleet and the Board of Quietly.” Straight ahead, high on a hill, surrounded by the 183 Longitude. The observatory’s origin might possibly have been acre Greenwich Park sits the Observatory. due to pillow talk, a whisper in the ear or a conversation over Climbing that long steep grade, digesting a breakfast of fried wine. Charles II, the Merrie Monarch, had as a mistress, Louise uncured bacon, eggs, bangers, pork and beans and tomatoes are de Keroualle, later the Duchess of Portsmouth, “the face that five land surveyors: 4 Yanks and 1 Brit. The climb is a culmina- saved a thousand ships.” She related to Charles an exciting story tion, the hajj for these surveyors, the once in a lifetime journey about a fellow Frenchman, Le Sieur de St. Pierre and his work to our Mecca: the Prime Meridian, Longitude and Time. solving the problem of longitude using only the heavens. The Observatory grounds proper, dominated by Flamsteed During Charles’ reign, the Great Plague and Great Fire of House, is a hodge-podge of structures assembled over three London occurred. Seeking diversions, Charles turned to the centuries of time. The contemporary surveyors would spend sciences to complement his investments in nautical enterprises. a number of hours traversing through narrow hallways, up Besides having an acknowledged dozen children and seven and down stairs and along stone pathways in beautiful weather mistresses, Charles greatly expanded the powers of the East >> By C. Barton Crattie, LS, CFM Displayed with permission • The American Surveyor • Vol. 10 No. 7 • Copyright 2013 Cheves Media • www.Amerisurv.com Easily visible from the Thames, a custom begun in 1833, the Greenwich time ball is dropped at precisely 1:00 p.m., allowing mariners of long ago to set their chronometers from their ships on the river below. OBSERVATORY Displayed with permission • The American Surveyor • Vol. 10 No. 7 • Copyright 2013 Cheves Media • www.Amerisurv.com quadrants and circles and the zenith sectors are mounted to solid stone walls oriented with the meridian. The stars are mapped and charted based on the precise time of their passing the meridian and by their elevation above the “horizon.” The prime meridian of the world, now illuminated at night by a laser, passes through the eyepiece of George Biddel Airy’s 1851 transit circle. In 1884, the international community met in Washington, DC and agreed to use the Greenwich meridian as the world’s prime meridian. In 1913, France finally adopted the meridian which they referred to as “Paris time diminished by 9 minutes and 21 seconds.” As part of this agreement, it is said that Britain The site of the observatory, high on a hill within the 183 acre Greenwich Park. promised to adopt the metric system. The Brits just didn’t say when. The world chose Airy’s meridian but India Company as well as chartering near the place where the Castle stood, with all of England is mapped using Bradley’s the Hudson’s Bay Company. On March lodging-rooms for our astronomical obser- meridian situated about 8 meters west. 4, 1675 the King named 28 year old vator and assistant . .” Flamsteed’s first James Bradley became 3rd Astronomer John Flamsteed “Royal Astronomical order of business was that he immediately Royal in 1742. The focal point in Observator.” Shortly thereafter, financed proved the Frenchman incompetent. Bradley’s transit room is the telescope through the sale of spoiled gunpowder, he used to chart more than 3,000 stars work began on Flamsteed’s new home and The Greenwich Meridian and establish the meridian that eventu- observatory. The site was chosen by Wren; A meridian is a line running in a north/ ally served as the basis for the famous a deserted castle with very strong existing south direction through the poles of the Ordnance Survey. foundation stones on high ground away earth’s rotation. There have been numer- from the lights and smoke of London. The ous meridians established for differing Royal Warrant stated in part: “Whereas, purposes over the years. Our country’s in order to the finding out of longitude rectangular system of survey has the of places for perfecting navigation and meridian as a primary element. astronomy, we have resolved to build Astronomers establish meridians to a small observatory within our park at map the heavens. The primary instru- Greenwich, upon the highest ground, at or ments of the observatory, the mural The main gate of the observatory is guarded by the 24 hour slave clock and the one time British standard for linear measurement. The prime meridian of the world originates within these windows, the three-part Meridian Building. Displayed with permission • The American Surveyor • Vol. 10 No. 7 • Copyright 2013 Cheves Media • www.Amerisurv.com Flamsteed’s meridian disappeared (from an old English astronomer) passes sea, developing the first isogonic lines. following his death and his wife selling through the observatory. Numeric designa- Unfortunately, declination does not his instruments. Evidence said to be tions increase east and west until both remain stationary. remnants of his 100 foot deep well zenith achieve 180 degrees at the international Tobias Mayer of Gottingen University sector and a portion of a quadrant built date-line. This is an arbitrary system, but in Germany was developing a system by Abraham Sharp are the few remain- one agreed to in 1884. (the one St. Pierre shared) of Lunar ing objects of Flamsteed’s 42 year tenure. Latitude is somewhat easy to determine distances. This system is fairly simple Edmund Halley’s iron quadrant by based on the position of Polaris or the and straight forward. Basically, the Graham (and meridian) is on the west sun at noon. Longitude, not so easy. One moon would be in a certain position in side of the same wall holding Bradley’s factor, known early on was a comparison relation to certain stars at precise times. (later) quadrant. of local times. Any number of solutions Observations and computations weren’t There is yet a 5th meridian at have been proposed over the centuries. that simple and straight forward though. Greenwich (unmarked). WGS84 placed A 1687 pamphlet advocated taking Nevil Maskelyne, the 5th Astronomer the 00 degrees location shown on one’s a wounded dog to sea. At a predeter- Royal as well as Charles Mason GPS receiver about 102.5 meters east of mined time, a timekeeper on shore devoted much of their time observing Airy’s meridian. This is due to adjust- would dip a bandage from the dog into and computing, adding to Mayer’s ments based on the earth’s center and not a powder. The dog at sea would yelp work. Unlike any of his predecessors, its surface. However, the good news is at that precise time and the crew would Maskelyne devoted his efforts solely to that because of the movement of tec- know the time ashore. the original charge of the Royal Warrant. tonic plates, the GPS meridian is moving Edmond Halley, 2nd Royal The end result was the Nautical Almanac, toward Airy’s line about 2.5 cm a year. Observator thought the answer might published in 1766, immediately selling Using a pretty good, but inexpensive lie in magnetism. Halley charted over 10,000 copies. Lunars remained in pocket compass, the American delegation declination on a number of voyages at checked Airy’s meridian. We found that it was fairly accurate, being just about 11-1/4 degrees east of north. Perhaps on With the city of London in the the next trip we’ll check declination. background, one of the observatory courtyards. In the foreground are the LonGiTude remains of what was once a 40 foot Lines of longitude are converging merid- Herschelian telescope and what is ians going either north or south from the purported to be the filled-in remains equator. As mentioned, “longitude naught” of Flamsteed’s 100 foot deep well zenith sector. One of John Bird’s quadrants (telescope is missing), this one being in the Octogon Room, designed by Christopher Wren. This quadrant is divided into 90 units as well as 96 units. Displayed with permission • The American Surveyor • Vol. 10 No. 7 • Copyright 2013 Cheves Media • www.Amerisurv.com Occupying both the eastern and use into the 19th century, well after the western hemispheres, this jolly one hour of time per 15 degrees of longi- advent of a reliable chronometer. group of surveyors experience the tude using GMT for the benchmark was The chronometer. The story of majesty of the Royal observatory. implemented. It’s no coincidence that one John Harrison and the years of clock Left to right: David Holland (Virginia), year later, the Greenwich meridian and design leading to H4 is well known. Chuck Dunlap (Virginia), Rich Leu mean time were agreed to internationally Though Maskelyne directed that the (Iowa), Steve Letchford, the Brit in Washington City.