🔍 Key Concepts

• Longitude vs. hour angle and how each is measured from a reference meridian • How angles are measured at the pole between two meridians • The meaning of terms like departure and polar arc in navigation

💭 Think About

• Ask yourself: when you stand at the pole, how do you measure the angle between the prime meridian and the meridian of a point on Earth? What is that angular quantity called? • Which of the options is specifically defined as an angle measured east or west from the prime meridian, and which is measured from Greenwich but used for celestial bodies? • Think about which term refers to distance along a parallel (east-west distance), and which terms refer to angular measurements on the sphere.

✅ Before You Answer

• Verify which option is an angular measurement between two meridians at the Earth’s center or pole, not a linear distance • Check which definition mentions being measured from the prime meridian through 180° east or west • Eliminate any term that is normally associated with time of a celestial body rather than a fixed geographic point on Earth