On 13 October at 1847 ZT, your vessel's DR...

Question 1 / 2066636eea28f7522a1c51aa98

Question 1 of 2066636eea28f7522a1c51aa98

On 13 October at 1847 ZT, your vessel's DR position is LAT 42°17.4' N, LONG 138°46.2' W. At approximately this time, you obtain a sextant altitude (hs) of Polaris reading 42°16.8', with an index error of 3.2' on the arc. Your chronometer reads 03h 45m 20s and is 1m 32s slow. What is your latitude by Polaris, given a height of eye of 44 feet?

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66636eea28f7522a1c51aa98

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🔍 Key Concepts

• Index error (IE) "on the arc" vs "off the arc" and how it changes sextant altitude • Dip correction for height of eye 44 feet when converting hs to observed altitude (Ho) • Relationship between Polaris observed altitude and latitude, including the small corrections from the Polaris tables in Bowditch or the Nautical Almanac

💭 Think About

• First, carefully convert the sextant altitude (hs) to the observed altitude (Ho). Think through the sign of the index error when it is "on the arc" and how the dip correction affects hs. • Once you have Ho, recall that Polaris’ altitude is approximately equal to the observer’s latitude, but needs small corrections from the Polaris tables. Consider whether those corrections will move your latitude slightly north or slightly south of Ho. • Compare your final latitude estimate to the DR latitude (42°17.4'N). Which choice is both consistent with the corrected Polaris altitude and reasonably close to your DR position?

✅ Before You Answer

• Be sure you apply index error of 3.2' "on the arc" with the correct sign before looking up any other corrections. • Verify you computed dip for 44 ft correctly (use the nearest value in the dip table; it will be a negative correction). • After applying Polaris corrections, check that your final latitude is within a few minutes of your DR latitude and that the direction of the change (north/south) matches the sign of your total corrections.

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Question 1 of 20

42°09.1'N

42°12.5'N

42°16.0'N

42°19.5'N

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Question 1 / 2066636eea28f7522a1c51aa98

Question 1 of 2066636eea28f7522a1c51aa98

Back

Question 1 of 20

66636eea28f7522a1c51aa98

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🔍 Key Concepts

💭 Think About

✅ Before You Answer

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