You observe the lower limb of the Sun at a...

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Question 1 of 2066636eea28f7522a1c51b410

You observe the lower limb of the Sun at a sextant altitude (hs) of 50° 26.9' on 9 November. The index error is 1.5' on the arc. The height of eye is 56 feet (17 meters). What is the observed altitude (Ho)?

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🔍 Key Concepts

• Index error (IE) correction: understand "on the arc" vs "off the arc" and how it changes the sextant altitude (hs) to get apparent altitude (Ha) • Dip (height of eye) correction: know that it is always applied in the same direction and depends on height of eye in feet or meters • Main altitude corrections for the Sun’s lower limb on the Ageton or Nautical Almanac tables (semidiameter + refraction + parallax)

💭 Think About

• First, decide whether you should add or subtract the 1.5' index error that is on the arc to get from hs to Ha. What is the sign of this correction? • Next, estimate the dip correction for a height of eye of about 56 feet (17 m). Is it more than 10', less than 5', or somewhere in between? • After you think about dip, recall whether the combined main correction for the lower limb of the Sun around 50° altitude is positive or negative and roughly how large it usually is.

✅ Before You Answer

• Be sure you correctly determine the sign of the index error when it is described as "on the arc". • Check that your dip correction magnitude makes sense for 56 ft: verify it is reasonable compared with typical values for 10 ft, 20 ft, etc. • After applying all corrections (IE, dip, main Sun correction), see which answer choice is closest to your expected direction and size of total change from 50° 26.9'.

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