🔍 Key Concepts

• Sextant altitude corrections (from sextant altitude to apparent altitude, then to observed altitude) • Which corrections are related to the eye and instrument versus the Earth and atmosphere • The specific meaning of apparent altitude vs observed altitude

💭 Think About

• List the usual sequence of corrections you apply starting from sextant altitude and note which part of the process gets each correction (index error, dip, refraction, semi‑diameter, parallax, etc.) • Ask yourself: by the time you already have apparent altitude, which effects have already been accounted for, and what is left to correct to reach observed altitude? • Consider which option is NOT tied to the step from apparent altitude to observed altitude but to some other stage or concept in sight reduction.

✅ Before You Answer

• Be clear on the definitions: sextant altitude (Hs), apparent altitude (Ha), observed altitude (Ho) • Verify which corrections deal with light bending in the atmosphere and shape/size of the celestial body • Check which choice refers to a correction that is connected to the geometric Earth center vs observer’s position, and decide whether that belongs in the apparent→observed step.