🔍 Key Concepts

• Azimuth angle definition in celestial navigation • Difference between a principal vertical circle and other circles like meridians or hour circles • Relationship between the observer, the celestial body, and the reference circle used for azimuth

💭 Think About

• Ask yourself: from what reference line on the sky do we normally measure azimuth toward a celestial body? • Which of these choices represents the great circle that actually passes through the celestial body and the observer’s zenith? • Which options are fixed reference circles (like meridians) versus a circle that depends on the body’s current position?

✅ Before You Answer

• Be clear on what the principal vertical circle is relative to your position (think about the north-south line through your zenith). • Identify which option names a circle that must pass through the celestial body itself. • Verify that azimuth is measured along the horizon from a reference direction toward the vertical circle of the body, not toward a general meridian.