🔍 Key Concepts

• Ex-meridian (ex-mer) sights and how they approximate a true meridian altitude when the body is slightly off the meridian • Step-by-step altitude corrections: converting hs → ha → Ho (index error, dip, refraction, etc.) • Using the meridian altitude formula for latitude: the relationship between latitude, declination, and zenith distance when the body is on (or nearly on) the meridian

💭 Think About

• First, if Venus were exactly on the meridian, how would you use the corrected observed altitude and the planet’s declination to get latitude? Think about whether Venus is due north or south and whether its declination has the same or contrary name as your DR latitude. • What does an ex-meridian correction do? Consider how far in time you are from true meridian passage (LAN) and how this small hour angle changes the altitude compared with the true meridian altitude. • Compare the latitudes you would get with a rough meridian-altitude estimate (ignoring ex-meridian correction) to the answer choices—then think about which direction (higher or lower latitude) the ex-meridian correction would push your result.

✅ Before You Answer

• Be sure you have correctly applied index correction (2.0' off the arc) and dip for 48 ft before doing any higher-level sight work. • Verify you are using the correct declination of Venus at the time of sight and that you’ve adjusted from chronometer time (with its error) to the proper time scale for the almanac. • Check the same name/contrary name rule carefully: when latitude and declination are the same name (both N or both S), latitude is related to declination plus or minus zenith distance in a specific way; when contrary name, the relationship reverses.