On 2 January you observe the lower limb of...

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Question 1 of 2066636eea28f7522a1c51ac2e

On 2 January you observe the lower limb of the Sun at a sextant altitude (hs) of 35° 50.4'. The index error is 0.8' on the arc. The height of eye is 24 feet (7.3 meters). What is the observed altitude (Ho)?

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Question 1 of 20

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🔍 Key Concepts

• Index error: Understand how to apply an index error that is "on the arc" to the sextant altitude (hs). • Dip (height of eye correction): How to convert height of eye in feet to a dip correction in minutes of arc, and whether it is added or subtracted. • Apparent altitude vs observed altitude (Ho): The sequence of corrections from hs → ha → Ho using the Nautical Almanac tables for the Sun’s lower limb.

💭 Think About

• First decide whether an index error that is "on the arc" makes the sextant reading too large or too small. Should this correction be added or subtracted from hs? • Next, compute the dip correction for a height of eye of 24 feet (7.3 m). Is dip always added or always subtracted from hs? • After applying index error and dip, think about what additional correction(s) are needed for the lower limb of the Sun to reach Ho, and whether the final Ho should be greater or less than the original hs.

✅ Before You Answer

• Be sure you apply the sign of the index error correctly: "on the arc" vs "off the arc". • Verify that the dip correction is in the correct units (minutes of arc) and has the correct sign. • Confirm that all corrections (index, dip, refraction, semidiameter, etc.) are applied in the correct order and that your final Ho is reasonable compared with the original hs (it should not differ by several degrees).

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