On 30 August in DR position LAT 26°34.0'N, LONG 141°36.0'W, you take an ex-meridian observation of the Sun's lower limb. The chronometer time of the sight is 09h 15m 26s, and the chronometer error is 00m 00s. The sextant altitude (hs) is 71°41.7'. The index error is 3.2' off the arc, and your height of eye is 49.6 feet. What is the latitude at meridian transit?
• Ex-meridian Sun sight method for latitude (when the Sun is near but not exactly on the meridian) • How to correct the sextant altitude: index error, dip, and apparent/true altitude corrections for the Sun’s lower limb • Using the Sun’s declination on 30 August and the relation between declination, true altitude at meridian passage, and latitude
• First, focus on getting from hs (71°41.7') to a correct observed altitude (Ho). What sequence of corrections must you apply, and what is the sign of each correction? • Once you have Ho, think about how ex‑meridian sights approximate the meridian altitude: how do you adjust for the time difference from local apparent noon? • When the Sun is south of you and on (or near) the meridian, how are latitude, declination, and meridian altitude related? Which combination of adding or subtracting declination from zenith distance leads to a northern latitude?
• Be sure you’ve applied the index error correctly: "off the arc" means the correction has a specific sign—verify which one. • Check that you’ve used the correct dip correction for a height of eye of 49.6 ft (convert to meters if needed or use the appropriate table). • Confirm whether the Sun’s declination on 30 August is north or south and whether the Sun is to the south or north of your DR latitude. This determines whether you add or subtract declination when solving for latitude.
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