On 10 March in DR position LAT 21°42.0'S, LONG 57°28.0'E, you take an ex-meridian observation of the Sun's lower limb. The chronometer time of the sight is 08h 28m 17s, and the chronometer error is 00m 00s. The sextant altitude (hs) is 72°08.0'. The index error is 3.4' on the arc, and your height of eye is 52.7 feet. What is the latitude at meridian transit?
• Ex-meridian Sun sight and how it relates to meridian altitude (HOnoon) and latitude • Correcting sextant altitude: index correction, dip (height of eye), and main Sun corrections from the Nautical Almanac • Using the Sun’s declination on 10 March and the relationship between latitude, declination, and meridian altitude
• First convert the sextant altitude (hs) to a true observed altitude (Ho). What corrections must you apply, and in what sign, given the index error and your height of eye? • For an ex-meridian sight taken a short time before or after LAN, how is the observed altitude adjusted to an equivalent meridian altitude? Think about the time difference from transit and the Sun’s change in altitude with time. • Once you have the meridian altitude and the Sun’s declination (same name or contrary name as your latitude?), what is the basic formula linking latitude, meridian altitude, and declination for a noon sight in your hemisphere?
• Be sure you apply index correction with the correct sign for an error "on the arc" and convert it to minutes of arc properly. • Confirm you have used the proper dip correction for 52.7 ft and applied the correct sign (does it increase or decrease the altitude?). • Verify whether you should add or subtract declination when solving for latitude, based on whether the Sun’s declination and your latitude are of the same or contrary names (both N/S or one N and one S).
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