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MIT 12 215 - Lecture Notes

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112.215 Modern NavigationThomas Herring ([email protected]),http:/geoweb.mit.edu/~tah/12.21510/13/2009 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)210/13/2009 12.215 Modern Naviation L08 3Todayʼs class• Sextant measurements using the sun:– We will track the sun to find its highest elevationand the time this occurs.• CAUTION: We will be looking at the sun with darkfilters on the sextant. Make sure the filters are inplace before measurements are made (they tend toflip out of the way when the scales are read).• Our one cheat will be using Computer NTP to get time10/13/2009 12.215 Modern Naviation L08 4Basic measurement• Since we can not see a level horizon from the classroom we will use a “poor-manʼs” artificial horizon (i.e.,a bowl of water).• Basic measurement will be to measure twice theelevation angle of sun (geometry shown on nextslide).• “Tricky” part is moving back and forth so that image ofsun from reflection can be seen. Basic measurementwith be to align the two images of the sun.310/13/2009 12.215 Modern Naviation L08 5Measurement geometryElevation angleElevation angleElevation angleMeasured angle is2*elevation angleMove back and forthto see reflectionLevel water surfaceOK: Letsget to


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MIT 12 215 - Lecture Notes

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