🔍 Key Concepts

• Greenwich Hour Angle (GHA) and how to correct chronometer time using the chronometer error (fast/slow) to get UTC • How to find Local Hour Angle (LHA) of Aries from your DR longitude, and then determine which stars are near that LHA and declination • Using the observed altitude (Ho) and the DR latitude to estimate the star’s declination and whether it is north or south of the equator

💭 Think About

• First, correct the chronometer time for its 3m 24s fast error. From that, determine UTC and then the GHA of Aries for that date and time. How does that narrow down which part of the sky you are looking at? • From your DR longitude and the GHA of Aries, compute LHA Aries. Then, think about each choice star’s Sidereal Hour Angle (SHA) and declination. Which one would be roughly at a true bearing of 097° and an altitude of about 48° at your DR position? • Use your latitude and the star’s approximate declination to judge whether a star at 48° altitude on a 097°T bearing should have a north or south declination and be east or west of your meridian. Which candidate matches that geometry best?

✅ Before You Answer

• Be sure you apply the chronometer correction in the correct direction: if the chronometer is fast, do you add or subtract the error to get true UTC? • Double-check the sign convention for longitude when computing LHA (LHA = GHA ± longitude). Are you east or west, and which way should you apply it? • Verify each candidate star’s SHA and declination from the star list and see which one’s computed azimuth and altitude best match 097°T and 48°20.0' at your DR position.