🔍 Key Concepts

• Ex-meridian (ex‑mer) sights and how they modify a meridian altitude problem • The standard meridian altitude latitude formula using observed altitude and declination • Correcting sextant altitude (hs) to observed altitude (Ho) for index error, height of eye, and Moon corrections

💭 Think About

• First, think about how you would find latitude from a perfect meridian altitude of a body at upper transit. What is the basic relationship between latitude, declination, and meridian altitude? • Then consider what makes this an ex‑meridian sight. How does a short time difference from true meridian passage affect the altitude, and do you correct the altitude up or down? • After you get a corrected Ho (including ex‑meridian correction), ask: Is the Moon north or south of your zenith, and is its declination same or contrary name to your latitude? How does that change the sign in the latitude formula?

✅ Before You Answer

• Be sure you have the correct GMT: apply the chronometer error properly and then convert to LMT using your DR longitude sign correctly (E longitudes give LMT ahead of GMT). • Apply all altitude corrections in the right direction: index error on the arc, dip for 40 ft, and the proper Moon corrections (SD, refraction, parallax) to get a realistic Ho near 48°. Make sure your final Ho is reasonable. • From the Almanac, confirm whether the Moon’s declination is N or S at the time and whether your formula should be ( \text{Lat} = 90^\circ - Ho + Dec ) or ( \text{Lat} = 90^\circ - Ho - Dec ). Use this to estimate whether the final latitude should end up north or south of the DR latitude and by roughly how many minutes to narrow the choices.