Circumpolar stars — observable behavior for a given latitude Which statement best characterizes circumpolar stars as seen from mid and high latitudes in the Northern Hemisphere?
-
AThey rotate around the north pole
-
BThey rotate around the celestial pole
-
CThey remain always above the horizon for the observer
-
DThey are seldom seen near the pole star
-
ENone of these
Answer
Correct Answer: They remain always above the horizon for the observer
Explanation
Introduction / Context:Circumpolar stars are important in navigation and surveying because they never set; their apparent motion provides useful reference directions throughout the night.
Given Data / Assumptions:
- Northern Hemisphere observer; analogous statements apply in the south with the south celestial pole.
- “Circumpolar” defined relative to observer’s latitude.
Concept / Approach:
A star is circumpolar if its declination satisfies conditions that keep its diurnal circle entirely above the horizon for that observer. Such stars circle the celestial pole without ever setting, thus are always visible (weather permitting).
Step-by-Step Solution:
Define circumpolar → star never dips below horizon.Hence, the key property is continuous visibility above the horizon.Therefore (c) is the most defining statement.Verification / Alternative check:
Diurnal circles drawn on the celestial sphere for high declinations show continuous paths above the horizon.
Why Other Options Are Wrong:
- (a) and (b) describe rotation about a pole but do not uniquely define “circumpolar”.
- (d) is incorrect; many circumpolar stars are indeed near Polaris.
Common Pitfalls:
- Assuming circumpolar status is global; it depends on latitude and star declination.
Final Answer:
They remain always above the horizon for the observer.