🔍 Key Concepts

• Apparent motion of stars relative to an observer on Earth • How a star’s azimuth (east/west) affects how its altitude changes as the Earth rotates • Relationship between a star’s position on the prime vertical (due east or due west) and its path across the sky

💭 Think About

• Picture yourself taking a series of sextant sights on a star that is due east or due west. How will its height above the horizon seem to change over a short time? • Compare how quickly altitude changes for a body near the meridian (due south or north) versus one low on the horizon to the east or west. • Think about Earth’s rotation: in 15° of hour angle per hour, what part of that motion shows up mainly as a change in altitude for a body in the east or west?

✅ Before You Answer

• Identify what happens to a star’s altitude when it is on or near the prime vertical (east or west of you). • Distinguish between motion along the horizon and motion up and down in altitude. • Make sure the choice you pick directly addresses the rate of change of altitude, not just general motion across the sky.