Question 1 of 27070
Q
On 25 December you observe the Sun's lower limb. The sextant altitude (hs) is 4°06.9'. The height of eye is 47-feet and the index error is 1.6' on the arc. The temperature is 19°F and the barometer reads 1030.8 millibars. What is the observed altitude (Ho)?
A
3°57.4'
B
4°01.9'
C
4°02.5'
D
4°03.4'
Question 1 / 2707066636ee928f7522a1c519099
Question 1 of 2707066636ee928f7522a1c519099

On 25 December you observe the Sun's lower limb. The sextant altitude (hs) is 4°06.9'. The height of eye is 47-feet and the index error is 1.6' on the arc. The temperature is 19°F and the barometer reads 1030.8 millibars. What is the observed altitude (Ho)?

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Question 1 of 27070
Q

On 25 December you observe the Sun's lower limb. The sextant altitude (hs) is 4°06.9'. The height of eye is 47-feet and the index error is 1.6' on the arc. The temperature is 19°F and the barometer reads 1030.8 millibars. What is the observed altitude (Ho)?

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🔍 Key Concepts

• Index correction: how to apply an error that is "on the arc" vs "off the arc" to get from hs to ha • Dip (height of eye): converting 47 feet to a dip correction in minutes of arc, and knowing its sign • Refraction and temperature/pressure corrections for a very low Sun altitude and very cold temperature

💭 Think About

• Start by adjusting hs for index error: should you add or subtract when the index error is noted as "on the arc"? • Next, compute the approximate dip correction for 47 ft. Is it usually added or subtracted from the sextant altitude? • Once you have apparent altitude, think about how low altitude, low temperature, and high pressure affect refraction: does this make the observed altitude larger or smaller than the apparent altitude?

✅ Before You Answer

• Be sure you convert 47 feet to dip in minutes correctly using the standard dip formula or table • Confirm the sign of each correction: index, dip, refraction, and any small additional corrections (e.g., semi‑diameter already built into lower limb Sun tables) • After applying all corrections step-by-step, check that your final Ho is within a few tenths of a minute of one of the answer choices before selecting it