Transcript The Quadrant

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.
Early Examples
• 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.
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 Latitude
http://www.longcamp.com/nav.html
• Epat: Scientific Instruments
http://www.mhs.ox.ac.uk/epact/
• National Maritime Museum
http://212.219.145.16/searchbin/searchs.pl?exhibit=thumbs&axis=ic0080e&flash=fals
e&dev
• How Columbus Navigated
http://vesuvius.jsc.nasa.gov/er/seh/navigate.htm
• Columbus Navigation
http://www1.minn.net/%7Ekeithp/index.htm