On 5 May at 1953 zone time, you take a sextant observation of Polaris. Your vessel's DR position is LAT 29°30.0'N, LONG 66°25.7'W, and your sextant reads 29°07.2'. Your chronometer reads 11h 51m 45s, and your chronometer error is 01m 36s slow. Your height of eye is 56 feet, and the index error for your sextant is 1.5' on the arc. What is the latitude of your vessel from your observation of Polaris?
• Using a sextant altitude to find Ho (observed altitude) from Hs (sextant altitude)**, including index correction and dip for height of eye • Special method for finding latitude from Polaris (not the same as a normal sight reduction), including the small corrections from the Nautical Almanac Polaris tables or sight reduction tables • Comparing the latitude from Polaris with your DR latitude to check if your result is reasonable
• First, carefully convert the sextant reading (Hs) to the true observed altitude (Ho). What corrections must you apply for index error and height of eye, and in which direction? • Once you have Ho, think about how close Polaris is to the North Celestial Pole. How does Ho of Polaris relate to your latitude, and what small corrections from the tables do you need to apply? • After you get a latitude value from Polaris, which of the choices is most consistent with both your computed result and your DR latitude of 29°30.0'N?
• Make sure you have applied index correction (IC) correctly: "on the arc" vs "off the arc" changes the sign of the correction • Confirm you used the correct dip (height of eye) correction for 56 feet, and that you converted it properly to minutes of arc • Verify that you applied the Polaris correction for your approximate latitude and local hour angle, and that your final latitude is close to your DR latitude (not many degrees away)
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