🔍 Key Concepts

• Great circle definition on the celestial sphere • Difference between meridians and parallels in celestial navigation • How celestial poles relate to circles that define celestial coordinates

💭 Think About

• Which type of circle on the celestial sphere must always run from the north celestial pole to the south celestial pole? • Which of these choices is specifically defined as a great circle going through a celestial body and both celestial poles, rather than just through the body and the observer? • Think about how hour angle and right ascension are measured—around what kind of circle are they measured?

✅ Before You Answer

• Confirm which option is explicitly defined as a great circle through both celestial poles • Eliminate any circle that is centered on or defined by the observer, not by the poles • Check your Bowditch or navigation text for the formal definition of diurnal circle, altitude circle, observer's meridian, and hour circle