On 23 September your 1836 DR position is LAT...

Question 1 of 2707066636eea28f7522a1c51ad64

On 23 September your 1836 DR position is LAT 25° 18' S, LONG 162° 23' E. You observe an unidentified star bearing 000° T at an observed altitude (Ho) of 26° 18'. The chronometer reads 07h 34m 12s, and is 01m 54s slow. What star did you observe?

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Question 1 of 27070

🔍 Key Concepts

• Use the chronometer correction (slow/fast) to get the correct UTC of the observation • From the date and time, find the GHA Aries, then add each star’s SHA (Sidereal Hour Angle) to get its GHA • From DR latitude/longitude and each star’s declination and LHA, check whether the resulting azimuth (Zn) and altitude (Hc) match a star on the meridian (bearing 000°T) at about 26° altitude

💭 Think About

• What is the correct UTC after applying the chronometer error, and what LHA Aries does that give you at your DR longitude? • For a star bearing 000°T, how should its declination compare to your DR latitude 25° 18' S (same name, greater/less than, or opposite name)? • Which of the listed stars, at that date and time, would transit (or be close to transit) your meridian at an altitude close to 26° 18' from latitude 25° S?

✅ Before You Answer

• Carefully apply the chronometer error: "01m 54s slow" means you must add that to the reading to get UTC • Confirm which candidate stars are circumpolar or not visible at about 25° S, and eliminate any that would be very low or below the horizon at meridian passage • For the remaining stars, verify that the computed Hc is close to the observed Ho = 26° 18' and that the computed Zn is essentially 000°T (on your meridian)