🔍 Key Concepts

• Difference between the true sun and the mean sun in nautical astronomy • Relationship between 24 hours and 360° of rotation • Difference between motion along the ecliptic and along the celestial equator

💭 Think About

• First decide whether the mean sun is defined to move at a constant rate or a variable rate. Which path (ecliptic or celestial equator) allows a simple, uniform measure of time? • Use Earth’s rotation: if Earth turns 360° in 24 hours, what angular rate (in degrees per hour) is used for timekeeping? • Ask yourself: is everyday civil time based on the Sun’s actual (true) apparent motion on the ecliptic, or on a simplified, averaged motion along a great circle tied to Earth’s equator?

✅ Before You Answer

• Verify whether 15° per hour or 15° per day matches a full 360° rotation in 24 hours • Confirm whether mean solar time is referenced to the celestial equator or to the ecliptic • Eliminate any option whose angular rate does NOT correspond to normal hourly timekeeping (24 hours in one full rotation)