On 15 July at 0447 ZT, your vessel's DR position is LAT 22°42' N, LONG 126°36' E. At approximately this time, you obtain a sextant altitude (hs) of Polaris reading 23°46.2' with an index error of 1.6' off the arc. Your chronometer reads 08h 48m 28s, and is 1m 16s fast. What is your latitude by Polaris, given a height of eye of 33 feet?
• Polaris latitude method – how Polaris altitude relates to observer’s latitude • Correcting sextant altitude: index error, height of eye (dip), and other small corrections • Using the chronometer error only to confirm date/time, not for a time-based sight reduction here
• First, carefully turn sextant altitude (hs) into an observed altitude (Ho). What exact sequence of corrections must you apply, and with what signs? • Once you have Ho for Polaris, think about how close Polaris is to the true North Pole and what small corrections must be added or subtracted to convert Ho into latitude. • Compare your Polaris‑derived latitude to the DR latitude. Which answer choices stay reasonably close after you apply all the proper corrections?
• Be sure you apply index error with the correct sign for “off the arc.” • Convert height of eye in feet to dip in minutes of arc correctly, and apply it with the proper sign. • Confirm the date (15 July) and approximate longitude to choose the proper Polaris correction (a small value in minutes), and check that your final latitude is consistent with the DR latitude.
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