On 14 January your 1922 DR position is LAT...

Question 1 of 2707066636eea28f7522a1c51aabd

On 14 January your 1922 DR position is LAT 27° 18.5' S, LONG 67° 18.0' E. You observe an unidentified star bearing 295° T at an observed altitude (Ho) of 13° 50.7'. The chronometer reads 03h 25m 43s, and is 03m 15s fast. What star did you observe?

Back

Question 1 of 27070

🔍 Key Concepts

• Chronometer error and GMT – how to apply a chronometer that is "fast" to get the correct time of observation in GMT • Local hour angle (LHA) of Aries and star – how to go from GMT and DR longitude to LHA to identify a star • Bearing vs. azimuth – relating the TRUE BEARING of the observed star to the computed azimuth from the sight reduction

💭 Think About

• Start by correcting the chronometer time: if the chronometer is fast, should you add or subtract the error to get the correct GMT of the sight? • From the corrected GMT and date, think about which sidereal hour angle (SHA) and declination would place each candidate star near the observed bearing and altitude from your DR position. • Compare which of the candidate stars would be visible at a true bearing near 295° and a low altitude (~14°) from a latitude of about 27° S at that time of year.

✅ Before You Answer

• Be sure you have the correct GMT of the sight after applying the chronometer error in the right direction. • Confirm that your DR longitude and latitude are used with the same sign convention (East positive, South negative) when finding LHA and computing azimuth/altitude. • Check that the star you choose has a declination and SHA that make sense for a westerly bearing around 295° and a low altitude from 27° S on 14 January.