On 16 December your 1810 zone time DR position is LONG 129°46.5'W. At that time, you observe Polaris with a sextant altitude (hs) of 23°56.8'. The chronometer time of the sight is 03h 12m 31s, and the chronometer error is 02m 16s fast. The index error is 2.5' off the arc, and the height of eye is 52.6 feet. What is your latitude by Polaris?
• Corrections to sextant altitude to find Ho (observed altitude), including index error and dip (height of eye) • Use of chronometer error to get the correct UTC of the sight, then determining LHA Aries from GHA Aries and DR longitude • How the Polaris tables in the Nautical Almanac relate Ho of Polaris to observer’s latitude using small corrections (a0, a1·sin LHA, a2·cos LHA)
• When hs is given and index error is "off the arc", do you add or subtract the index correction to get ha? After that, how do dip and other corrections change the altitude to reach Ho? • Chronometer is 2m 16s fast. Does that mean the actual UTC is earlier or later than the reading? Once you have correct UTC, how do you use the Nautical Almanac to find GHA Aries for that exact time? • After you obtain Ho and have LHA Aries, how do the Polaris correction terms (from the Almanac table) adjust Ho to give latitude, and are the corrections added or subtracted for your hemisphere and LHA range?
• Be sure the signs of all corrections (index error, dip, and Polaris corrections) are handled correctly • Verify you use DR longitude with the correct east/west sign convention when computing LHA Aries • Confirm you are using the Polaris section of the Nautical Almanac for 16 December, not a general star table, and that you apply all its listed correction terms before choosing the closest latitude option
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