Which point is where the plumb line projected above horizon meets the celestial sphere?

Which point is where the plumb line projected above horizon meets the celestial sphere?

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

Answer: (A)

The main idea here is the zenith—the point on the celestial sphere that lies directly above the observer. The plumb line shows the vertical direction due to gravity; when you extend it upward, it meets the sky at the zenith, the point overhead. The opposite point below the horizon is the nadir, not the sky-facing direction. The celestial poles are fixed points related to Earth’s axis, not the vertical overhead direction, and the celestial equator is a great circle tracing Earth’s equator on the sky, not the overhead point. So the intersection of the vertical with the celestial sphere is the zenith.

The main idea here is the zenith—the point on the celestial sphere that lies directly above the observer. The plumb line shows the vertical direction due to gravity; when you extend it upward, it meets the sky at the zenith, the point overhead. The opposite point below the horizon is the nadir, not the sky-facing direction. The celestial poles are fixed points related to Earth’s axis, not the vertical overhead direction, and the celestial equator is a great circle tracing Earth’s equator on the sky, not the overhead point. So the intersection of the vertical with the celestial sphere is the zenith.