On 28 October at 1754 ZT, your vessel's DR...

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Question 1 of 2066636eea28f7522a1c51add0

On 28 October at 1754 ZT, your vessel's DR position is LAT 28° 30' N, LONG 63° 24' W. At this time, you obtain a sextant altitude (hs) of Polaris reading 28° 42.6', with an index error of 2.4' on the arc. Your chronometer reads 09h 50m 00s, and is 4m 14s slow. What is your latitude by Polaris, given a height of eye of 28 feet (8.5 meters)?

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🔍 Key Concepts

• Polaris (Pole Star) latitude method: How Polaris’ observed altitude relates to your latitude in the Northern Hemisphere. • Sextant altitude corrections: Index error, dip (height of eye), and small additional corrections to go from hs → Ho (observed altitude). • The effect of chronometer error and date on using Polaris tables in the Nautical Almanac (or equivalent).

💭 Think About

• First, carefully correct the sextant altitude (hs) for index error and dip to get the apparent/observed altitude. Is the index error on the arc added or subtracted? • Think about how close the altitude of Polaris is to your DR latitude. Should the final latitude be slightly greater than, less than, or about the same as the DR latitude (28° 30' N)? • Consider whether the date (late October) and hour (near local evening) would make Polaris appear slightly above or below the true pole, and how the Nautical Almanac’s Polaris corrections adjust for that.

✅ Before You Answer

• Be sure you apply index error in the correct direction: "on the arc" vs "off the arc" changes whether you add or subtract. • Confirm you use the correct dip correction for a height of eye of 28 ft (8.5 m) and apply it with the correct sign (it is always subtracted from the sextant altitude). • After computing Ho for Polaris and applying the proper Polaris corrections from the Almanac, check that your final latitude is reasonable compared to the DR latitude (not wildly different).

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