On 22 May at 0440 ZT, your vessel's DR...

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Question 1 of 2066636eea28f7522a1c51ad17

On 22 May at 0440 ZT, your vessel's DR position is LAT 23° 24' N, LONG 110° 24' W. At approximately this time, you obtain a sextant altitude (hs) of Polaris reading 23° 40.9' with an index error of 1.6' on the arc. Your chronometer reads 11h 42m 14s, and is 2m 36s fast. What is your latitude by Polaris, given a height of eye of 24 feet?

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🔍 Key Concepts

• Polaris (Pole Star) latitude method – how Polaris altitude relates to observer’s latitude in the Northern Hemisphere • How to correctly reduce a sextant altitude: apply index correction, dip (height of eye), and then any small corrections for Polaris from the Nautical Almanac • Difference between DR latitude and latitude by Polaris, and how large you’d expect that difference to be for a normal observation

💭 Think About

• First, carefully reduce the sextant altitude (hs) to an observed altitude (Ho). Are you adding or subtracting the index error here? What about dip for a 24‑ft eye height? • Once you have Ho, think about how Polaris’ altitude compares to your latitude at about 23° N. Is it exactly the same, or do you need to apply a small correction from the Almanac tables for Polaris? • Compare the resulting latitude by Polaris with your DR latitude. Does the result make sense physically (i.e., is it reasonably close to your DR and in the correct hemisphere)?

✅ Before You Answer

• Be sure you apply the index correction with the correct sign for an error "on the arc". • Use the correct dip correction for a 24‑ft height of eye – check typical dip values per 10 ft and confirm the sign. • From the Nautical Almanac, confirm the proper Polaris corrections (a0, a1, etc.) for the approximate LHA Aries/date, and be sure you understand whether they are added to or subtracted from Ho before calling the result your latitude.

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