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# Sextant

Amy, Fatima
by

## lake anne 6

on 28 May 2010

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#### Transcript of Sextant

Sextant Invented by John Hadley in 1731 in England By: Amy and Fatima By: Amy and Fatima The defintion of A Sextant is an astronomical instrument used to determine latitude and longitude at sea by measuring angular distances, esp. the altitudes of sun, moon, and stars. From http://dictionary.reference.com/browse/Sextant
First, imagine we have two mirrors offset from each other and labeled as Horizon Glass Q" and Index
Mirror Q# shown in Figure " below. We also assume the planes of the two mirrors are parallel to each >>>

Info By : homepage.smc.edu/kennedy_john/SEXTANT.PDF other, meaning line EF ² HJ Þ Furthermore, assume that the Horizon Glass Q is such that when
Ó Ó
"
sunlight is reflected off the Index Mirror Q# and subsequently into and away from Q", that the sunlight
from Q" travels in a perfectly horizontal line to an observer's eye point I. This second assumption just >>>

Info By:
homepage.smc.edu/kennedy_john/SEXTANT.PDF means we have positioned both mirrors with a slight off-vertical orientation so that the line LI is
Ó
perfectly horizontal. In Figure ", the angles of incidence and reflection off both mirrors is the same as is
indicated by using the same numeric labels for the two pairs of angles associated with the sunlight and
both mirrors. The lines GO and LK in Figure " are normal or perpendicular to each mirror's reflecting >>>

Info By:
homepage.smc.edu/kennedy_john/SEXTANT.PDF surface and thus make right angles to their respective mirrors and to the two lines EF and HJ . n" is
Ó Ó
both an angle of incidence and an angle of reflection for the sunlight that strikes and reflects off both
mirrors. The Index Mirror Q2 will be allowed to rotate about its center point G. The reason for having >>>

Info By:
homepage.smc.edu/kennedy_john/SEXTANT.PDF two mirrors is so a person can sight both the horizon and an object in the sky at the same time with one
eye and one sight. Figure " is an un-realistic initial presentation of a sextant. Figure # on the next page is
more realistic in terms of illustrating the true geometry of a mechanical two-mirror sextant

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homepage.smc.edu/kennedy_john/SEXTANT.PDF The Sextant was invented to help shipsmen to find where they are located on the earth.
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