12.215 Modern NavigationReview of last LectureToday’s classBasic measurementMeasurement geometry12.215 Modern NavigationThomas Herring10/23/2006 12.215 Modern Naviation L08 2Review of last Lecture• Dead reckoning and conventional navigation– Magnetic North pole– Distance measurements• Use of Sextant– Principles of instrument– Vernier Scale reading (ex. Pierre Vernier (1580?–1637), French mathematician.)– Corrections needed for sextant measurements– (Next class we make sextant measurements)10/23/2006 12.215 Modern Naviation L08 3Today’s class• Sextant measurements using the sun:– We will track the sun to find its highest elevation and the time this occurs.• CAUTION: We will be looking at the sun with dark filters on the sextant. Make sure the filters are in place before measurements are made (they tend to flip out of the way when the scales are read).• Our one cheat will be using GPS to get time (and to check the results)10/23/2006 12.215 Modern Naviation L08 4Basic measurement• Since we can not see a level horizon from the class room we will use a “poor-man’s” artificial horizon (i.e., a bowl of water).• Basic measurement will be to measure twice the elevation angle of sun (geometry shown on next slide).• “Tricky” part is moving back and forth so that image of sun from reflection can be seen. Basic measurement with be to align the two images of the sun.10/23/2006 12.215 Modern Naviation L08 5Measurement geometryElevation angleElevation angleElevation angleMeasured angle is2*elevation angleMove back and forthto see reflectionLevel water surfaceOK: Lets get to
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