On 18 October at 0518 ZT, morning stars were...

On 18 October at 0518 ZT, morning stars were observed and the vessel's position was determined to be LAT 25° 31.0' N, LONG 146° 29.2' E. Your vessel is steaming at 19.0 knots on a course of 308° T. A sextant observation of the Sun's lower limb is made at 0915 ZT. The chronometer reads 11h 17m 11s, and the sextant altitude (hs) is 34° 51.4'. The index error is 2.0' off the arc, and the chronometer error is 01m 57s fast. Your height of eye on the bridge is 54.0 feet. What is the azimuth (Zn) of this sight using the assumed position?

🔍 Key Concepts

• Local time vs. UTC (GMT) conversion using zone description (ZD) to get correct GHA and declination from the Nautical Almanac • How to compute true altitude (Ho) from sextant altitude (Hs), including index correction, height of eye (dip), and other corrections • Using the assumed position (AP) with calculated altitude (Hc) and local hour angle (LHA) to determine the Sun’s azimuth (Zn) from the sight reduction tables or formulas

💭 Think About

• What is the correct GMT of the sight after applying the chronometer error, and how does that compare to the ZT of the sight using the zone description from your longitude? • Once you have the Sun’s GHA and declination for the correct time, how do you form LHA and then use Lat, Dec, and LHA to determine whether the Sun is in the NE, SE, SW, or NW quadrant? • Given your latitude and the Sun’s declination, should you expect an azimuth closer to east, southeast, or south, and how would that help you eliminate some answer choices that don’t fit the geometry of the problem?

✅ Before You Answer

• Be sure you apply index error with the correct sign ("off the arc" vs. "on the arc") when correcting Hs to get Ho. • Verify you have the correct zone description (ZD) sign for 146° E longitude so that your conversion between ZT and GMT is in the correct direction. • Double‑check that your final Zn is expressed as a true bearing from 000° to 359°, and that the quadrant (NE/SE/SW/NW) matches the relative position of the Sun based on your AP, declination, and time of day.