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

Question 1 of 2707066636eea28f7522a1c51b40e

You observe the lower limb of the Sun at a sextant altitude (hs) of 45°49.7' on 13 November. The index error is 1.0' on the arc. The height of eye is 61 feet (18.6 meters). What is the observed altitude (Ho)?

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Question 1 of 27070

🔍 Key Concepts

• Index correction (IC): how to apply it when the sextant reads "on the arc" versus "off the arc" • Dip (height of eye correction) for a height of eye of 61 feet / 18.6 meters • Lower limb Sun corrections: main table used and approximate size of refraction + semidiameter at about 46° altitude

💭 Think About

• First, decide the sign of the index correction from an index error of 1.0' "on the arc". Should this be added to or subtracted from hs? • Next, estimate the dip for 61 feet and apply it to get an apparent altitude. Does dip increase or decrease the sextant altitude? • Then consider whether the combined Sun corrections (refraction + semidiameter at ~46° altitude for lower limb) will move your result up or down, and by roughly how many minutes.

✅ Before You Answer

• Be sure you have the correct sign for the index correction when the error is "on the arc" • Use a realistic dip value for 61 feet (on the order of a few minutes, not tens of minutes) • Check that your final Ho is reasonable: it should differ from hs by less than about 10' overall for this situation