On 5 May in DR position LAT 38°34.5'N, LONG 124°20.7'W, you take an ex-meridian observation of the Sun's lower limb. The chronometer time of the sight is 07h 59m 10s, and the chronometer error is 01m 10s slow. The sextant altitude (hs) is 67°27.0'. The index error is 1.4' on the arc, and your height of eye is 30 feet. What is the latitude at meridian transit?
• Ex-meridian Sun sight method for latitude (what quantity you ultimately combine with the corrected Ho) • Proper sequence of sextant altitude corrections: index error, dip (height of eye), then main altitude corrections from the Nautical Almanac • Using chronometer time + chronometer error to get correct GMT, and then getting the Sun’s declination for that exact time
• What is the purpose of an ex-meridian sight, and how is the final latitude related to the Sun’s maximum altitude and its declination? • After you correct the sextant altitude (hs) to get Ho, in which direction (add or subtract) will you apply the ex-meridian correction to reach the equivalent meridian altitude? • Given the date and approximate DR longitude, is the Sun to the north or south of you at meridian passage, and does this mean you add or subtract the declination when solving for latitude?
• Be sure you have applied index correction (on the arc vs off the arc) with the correct sign before doing any further corrections. • Confirm that you converted chronometer time to GMT correctly by applying the chronometer error (slow vs fast) with the right sign. • Verify you are using the correct declination for the exact time of the sight and that you chose the proper ex-meridian correction from the tables for the Sun’s changing altitude.
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