In the Bay of Fundy, during twilight, you a take sight of Mars. The sextant altitude (hs) is 03° 35.5'. Your height of eye is 32 feet and there is no index error. The air temperature is -10° C and the barometer reads 1010 millibars. What is the observed altitude (Ho)?
• Sextant altitude vs. observed altitude and the sequence of corrections (index error, dip, refraction, etc.) • How height of eye (dip) affects the sextant altitude at very low altitudes • How temperature and pressure change the refraction correction for a planet like Mars at about 3–4° altitude
• First, adjust hs for height of eye using the standard dip formula or table for 32 feet. How many minutes does that subtract? • Then, think about what corrections you apply for a planet: do you use semi‑diameter, or mainly refraction (plus any small planetary correction from the Nautical Almanac)? • Compare the size of the total correction at such a low altitude with the answer choices: should Ho end up closer to 3°25' or closer to 3°15'?
• Be sure you have subtracted dip correctly for 32 feet before doing any atmospheric corrections. • Use the proper refraction correction for a low-altitude body with T = –10° C and P = 1010 mb (colder air means stronger refraction). • Confirm whether Mars uses the same main altitude correction table as stars/planets, and that you are NOT adding a Sun/Moon semi‑diameter correction.
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