Which term refers to the points on the celestial sphere where Earth's polar axis would pierce the sphere?

Which term refers to the points on the celestial sphere where Earth's polar axis would pierce the sphere?

• A. Celestial poles
• B. Zenith
• C. Nadir
• D. Celestial axis

Answer: (A)

The main idea is to picture Earth’s rotation axis extended into space and where that axis crosses the celestial sphere. It hits at two opposite points, called the celestial poles—the north celestial pole and the south celestial pole. They define where the axis “pierces” the sky and stay fixed relative to the stars (apart from very slow movement due to axial precession). The zenith is just the point directly overhead from your location, and the nadir is directly below you—both are observer-specific ideas, not the axis intersection points. The term celestial axis refers to the imaginary line of Earth's rotation, not the points where it meets the celestial sphere. So the term for those two intersection points is celestial poles.

The main idea is to picture Earth’s rotation axis extended into space and where that axis crosses the celestial sphere. It hits at two opposite points, called the celestial poles—the north celestial pole and the south celestial pole. They define where the axis “pierces” the sky and stay fixed relative to the stars (apart from very slow movement due to axial precession). The zenith is just the point directly overhead from your location, and the nadir is directly below you—both are observer-specific ideas, not the axis intersection points. The term celestial axis refers to the imaginary line of Earth's rotation, not the points where it meets the celestial sphere. So the term for those two intersection points is celestial poles.