The Quadrant An astronomical instrument that is 1/4 of a circle or 90 degrees. It is used to measure...
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Transcript of The Quadrant An astronomical instrument that is 1/4 of a circle or 90 degrees. It is used to measure...
The Quadrant
•An astronomical instrument that is 1/4 of a circle or 90 degrees. It is used to measure the altitude of stars, or measure the latitude of the north star.
• Describe as a ‘plinth’ around 150 A.D. by Claudius Ptolemy in his Almagest. The ‘plinth’ cast a shadow on to a 90 degree arc.
• Islamic astronomers had mural quadrants that were fixed in the meridian plane and altazimuth quadrants that could be moved to determine altitude and azimuth of a celestial body.
• Tycho Brahe completed large quadrants, up to 2 meters in radius, in the 1580s.
Early Examples
The Octant and Sextant
• Both these instruments were used to get the same information as a quadrant with less accuracy.
• The octant is a quadrant which is folded making it more compact and easier to use. Its accuracy is less because the scale markings are twice as close.
• The sextant is 1/6 of a circle opposed to the 1/4 quadrant. Its is almost as accurate and easy to use, although it is light.
Columbus
• On November 2, 1942, Columbus wrote in his log that he made a quadrant sighting of the North Star.
• He used dead reckoning, deducing your position, and also used this with the quadrant to tell where he was on a map.
Drake
• While Drake thought he was at 38 degrees 30 minutes he was probably closer to 38 degrees 19 minutes.
• Most historians believe that he landed at 38 degrees 2 minutes, Marin County's Drakes Bay .
How to Use the Quadrant
• Step 1: Line the sights up to North Star.
• Step 2: Hold the plumb-line to the arc, and take the reading in degrees as close as you can.
• Step 3: Read the angle and that would be the latitude.
Sources
• Francis Drake’s determination of Latitudehttp://www.longcamp.com/nav.html
• Epat: Scientific Instrumentshttp://www.mhs.ox.ac.uk/epact/
• National Maritime Museumhttp://212.219.145.16/searchbin/searchs.pl?exhibit=thumbs&axis=ic0080e&flash=false&dev
• How Columbus Navigatedhttp://vesuvius.jsc.nasa.gov/er/seh/navigate.htm
• Columbus Navigationhttp://www1.minn.net/%7Ekeithp/index.htm