On 14 March at 1845 ZT, you take a sextant observation of Polaris. Your DR position is LAT 29°10'N, LONG 154°30'W, and your sextant reads 29°53.5'. Your chronometer reads 04h 42m 36s, and the chronometer error is 02m 24s slow. Your height of eye is 24 feet, and the index error is 1.3' off the arc. Determine the latitude by Polaris.
• Polaris altitude corrections (index error, dip for height of eye, and other small corrections) • Relationship between observed altitude of Polaris (Ho) and observer’s latitude • Use of chronometer time and longitude to find the correct Polaris correction from tables
• First, carefully correct the sextant altitude (Hs) for index error and dip. What is your final Ho for Polaris? • Once you have Ho, think about how close Polaris is to the true North Pole. How is latitude related to Ho for Polaris, and what small correction must be applied from the tables? • How do the date (14 March), your longitude, and the corrected time help you pick the proper Polaris correction value before adding/subtracting it from Ho?
• Be sure the index error sign is applied correctly: "off the arc" vs "on the arc" • Confirm your dip correction for a 24‑ft height of eye and subtract it from Ha • Verify you are using the proper Polaris correction for the correct LHA and date before comparing your computed latitude with the choices
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