On 15 August an ex-meridian altitude of the...

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Question 1 of 2066636eea28f7522a1c51aad8

On 15 August an ex-meridian altitude of the Sun's lower limb at upper transit was observed at 1130 ZT. Your DR position is LAT 26° 24.0' S, LONG 155° 02.0' E, and your sextant altitude (hs) is 48° 45.9'. The index error is 2.6' on the arc, and your height of eye is 51.5 feet. The chronometer time of the observation is 01h 27m 38s, and the chronometer error is 02m 14s slow. Find the latitude at meridian transit from the ex-meridian observation.

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Question 1 of 20

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🔍 Key Concepts

• Ex-meridian altitude correction method and why it is used instead of a perfect meridian passage • How to convert sextant altitude (hs) to observed altitude (Ho) using index error and dip • Relationship between Sun’s declination at upper transit and observer’s latitude when the Sun is north/south of your position

💭 Think About

• First, work carefully from hs to Ho: how do you apply an index error that is on the arc and a height of eye in feet? What sign should each correction have? • Think about 15 August: is the Sun’s declination likely to be north or south? Given you are in 26° S, is the Sun north or south of you at local noon, and what does that do to the latitude formula? • For an ex‑meridian sight, the Sun was not exactly on the meridian at the time of observation. What additional correction must be applied to the altitude (or latitude) to account for the time difference from meridian passage, and how does the sign of that correction depend on whether the Sun is increasing or decreasing in altitude?

✅ Before You Answer

• Confirm the correct sign for the index error when it is stated as "2.6' on the arc" before applying it to hs. • Use sight reduction tables or formulas to obtain the true declination of the Sun for the correct GMT of the observation, being careful with chronometer error and longitude to get the right meridian passage time. • Before choosing an answer, check whether your final latitude should be greater or smaller than your DR latitude based on whether the corrected Ho is greater or less than you would expect at meridian passage.

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