On 22 February your 1857 DR position is LAT...

Question 1 of 310488R0ro14k3hjFBjBuQslt

On 22 February your 1857 DR position is LAT 23°46.0'S, LONG 93°16.5'E. You observe an unidentified star bearing 126°T at an observed altitude (Ho) of 40°21.5'. The chronometer reads 01h 00m 35s and is 03m 25s fast. What star did you observe?

Back

Question 1 of 31048

🔍 Key Concepts

• Sidereal Hour Angle (SHA) and declination (Dec) of stars from the Nautical Almanac for 22 February at 01h GMT • Relationship between Local Hour Angle (LHA), longitude, and Greenwich Hour Angle (GHA) of Aries to identify a star • How the computed altitude (Hc) and computed azimuth (Zn) from your DR position help match the observed star with one of the choices

💭 Think About

• Convert the chronometer time to UTC (GMT) using the chronometer error, then determine GHA Aries for that time and date • From your DR longitude, find the Local Hour Angle of Aries (LHA Aries), then use the star atlas or star tables to see which candidate star lies near the observed azimuth and altitude • For each answer choice, compare its predicted altitude and bearing (from sight reduction) with your observed Ho and Zn to see which is the closest match

✅ Before You Answer

• Be sure you are using the correct sign for the chronometer error (fast vs slow) when finding GMT • Confirm you are using west-positive, east-negative (or the convention given in your tables) consistently when computing LHA from GHA and longitude • Verify that the star you select has a computed altitude and azimuth that agree with the observation within a small, realistic intercept (few miles)