On 28 July your 0800 zone time fix gives you a position of LAT 25° 16.0' N, LONG 71° 19.0' W. Your vessel is on course 026° T, and your speed is 17.5 knots. Local apparent noon (LAN) occurs at 1149 zone time, at which time a meridian altitude of the Sun's lower limb is observed. The observed altitude (Ho) for this sight is 82° 28.7'. What is the calculated latitude at LAN?
• Meridian passage (LAN) sights for latitude: relationship between observed altitude (Ho), zenith distance, and declination • How to compute DR latitude at LAN from course, speed, and time run from the morning fix • The noon-sight latitude formula using zenith distance (co-altitude) and the Sun’s declination and bearing (N or S of you)
• From 0800 to 1149, how long do you steam, and how many miles north/south do you travel along your track? How does that change your latitude? • At LAN, the Sun is on your meridian. How do you get zenith distance from Ho, and then combine it with the Sun’s declination to get latitude? • On 28 July, is the Sun’s declination north or south, and is the Sun to the north or south of your zenith at your latitude? How does that affect whether you add or subtract zenith distance and declination?
• Compute run in time from 0800 to 1149, then distance = speed × time; convert the north-south component of that run into minutes of latitude and update your DR latitude for 1149 • Make sure you correctly find zenith distance: ( z = 90^\circ - Ho ) • Confirm whether to use Lat = Dec ± z or Lat = |Dec ± z|, based on whether you and the Sun are in the same or opposite hemispheres and whether the Sun is north or south of your zenith
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