On 11 March your 1846 zone time DR position...

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Question 1 of 2066636eea28f7522a1c51aa1c

On 11 March your 1846 zone time DR position is LAT 25° 05.7' N, LONG 124° 29.0' W. At that time you observe Polaris with a sextant altitude (hs) of 25° 59.1'. The chronometer time of the sight is 02h 44m 01s, and the chronometer error is 02m 15s slow. The index error is 3.9' on the arc, and the height of eye is 42.7 feet (13.0 meters). What is your latitude by Polaris?

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🔍 Key Concepts

• Polaris latitude method – how Polaris altitude relates to observer’s latitude in the Northern Hemisphere • Correcting sextant altitude: index error, dip (height of eye), and other corrections to get observed altitude (Ho) • Small corrections for Polaris (its offset from the true North Celestial Pole and effect of longitude/date)

💭 Think About

• Start by converting the sextant altitude (hs) to the true observed altitude (Ho). What specific corrections do you need and in what direction do you apply them? • Once you have Ho for Polaris, think about how closely Polaris altitude matches your latitude and what small adjustments must be made for its position relative to the pole. • Use the date and longitude to decide whether you need to add or subtract a small correction from Ho to estimate your latitude. How large is this correction likely to be?

✅ Before You Answer

• Be sure you applied index error correctly: is ‘on the arc’ added or subtracted? • Confirm the dip correction (for height of eye) is in the correct direction and reasonable in size for 42.7 ft. • After all corrections, compare your final latitude estimate with the DR latitude to see if it is reasonable and consistent.

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