On 25 February at 0622 ZT, you observe the...

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Question 1 of 2066636eea28f7522a1c51ad9c

On 25 February at 0622 ZT, you observe the upper limb of the Moon with a sextant altitude of 59° 58.6'. Your DR position is LAT 30° 28.3' S, LONG 102° 39.3 E. The chronometer reading at the time of the sight is 11h 21m 18s and the chronometer is 48s slow. The height of eye is 59 feet and the index error is 2.5' on the arc. What are the azimuth (Zn) and intercept (a) of this sight using the assumed position?

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Question 1 of 20

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🔍 Key Concepts

• Time conversion from ZT and chronometer reading (including chronometer error) to correct Greenwich Hour Angle (GHA) of the Moon • Applying sextant corrections in the proper order: index error, height of eye (dip), and main altitude corrections (including for upper limb of the Moon) to find Ho (observed altitude) • Using the assumed position (AP) to compute Hc (computed altitude) and Zn (azimuth), then comparing Ho and Hc to find the intercept (toward or away)

💭 Think About

• First, how do you combine the sextant altitude, index error, and dip to get the apparent altitude, and then apply Moon corrections to reach Ho? Think carefully about the signs of each correction. • From the DR longitude and the corrected time, how do you determine the local hour angle (LHA) of the Moon, and how does LHA help set up the sight reduction for Hc and Zn? • Once you have Ho and Hc, how do you decide whether the intercept is toward (T) or away (A) and how large it is in minutes of arc? How does that help you eliminate some answer choices?

✅ Before You Answer

• Verify the sign of the index error ("on the arc" vs "off the arc") and how it affects Ha. • Confirm you are using the correct limb correction and parallax for the upper limb of the Moon from the sight reduction tables/NA for the given date and time. • Double-check the relationship between Ho and Hc: if Ho > Hc, the intercept is toward, and if Ho < Hc, the intercept is away. Use this to rule out inconsistent options.

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