🔍 Key Concepts

• Selection criteria for three-body star fixes (good spread in azimuth, suitable altitudes, brightness/magnitude) • Use of Polaris (mainly for latitude, and its effect on azimuth spread and fix quality) • Practical issues with using the Moon and planets in a star fix (rapid motion, semidiameter, glare, and altitude limits)

💭 Think About

• For each choice, imagine where those bodies would be in the sky from 28° N, 168° E around 0300 ZT in late April. Which group would give you three lines of position that cross with a wide, even spread? • Think about ideal altitude limits for star sights (not too low near the horizon, not nearly overhead). Which option is most likely to give you three sights all within that useful altitude band? • Consider which bodies are typically chosen for routine three‑body fixes in exam problems: are slow‑moving stars preferred, or bodies like the Moon and Polaris that are usually used for special purposes?

✅ Before You Answer

• Verify which option gives three bodies with well‑separated azimuths (roughly 60°–120° apart, not all on the same side of the sky). • Check which bodies are likely to have altitudes between about 15° and 75° at that DR position and time. • Confirm whether including Polaris or the Moon would improve or worsen the overall geometry and reliability of a three‑body fix, based on how they are normally used in celestial navigation.