Astronomy Ranking Task: Motion Of The Sky Exercise #5 Description: The Figure Below Shows The Evening Sky As It Would Appear While Looking North At 9PM Tonight For An Observer In The Northern Hemisphere. Notice That Polaris, The North Star, Appears Fairly High In The Sky – While Other Stars (Labeled A-D) Appear To Slowly Move Counter-Clockwise In Great
The Correct Answer and Explanation is :
In Exercise #5 of the Astronomy Ranking Task: Motion of the Sky, the objective is to rank stars A through D based on the duration they remain above the horizon during a 24-hour period. The observer is situated in the Northern Hemisphere, facing north at 9 PM. Polaris, the North Star, is positioned high in the sky, with the other stars (A–D) appearing to move counterclockwise in great circles around it.
Ranking the Stars:
- Star D: This star traces a complete circle around Polaris, remaining above the horizon for the entire 24-hour period.
- Star A: Located closer to Polaris, Star A follows a smaller circle, spending more time above the horizon than Stars B and C.
- Star B: Positioned farther from Polaris than Star A, Star B traces a larger circle, resulting in less time above the horizon.
- Star C: The farthest from Polaris, Star C follows the largest circle, spending the least amount of time above the horizon.
Explanation:
The apparent motion of stars in the Northern Hemisphere is due to Earth’s rotation. Stars near Polaris, such as Star D, appear to move in small circles around the North Star, remaining above the horizon for longer periods. As the distance from Polaris increases, the circles become larger, and the stars spend less time above the horizon. This results in Star D being visible throughout the night, Star A for a significant portion, Star B for less time, and Star C for the least amount of time.
This pattern is consistent with the concept of circumpolar stars, which are stars that never set below the horizon for a given observer’s location. The closer a star is to the celestial pole (near Polaris), the more circumpolar it is, and the longer it remains visible throughout the night.
Understanding this motion is fundamental in astronomy, as it explains the daily and seasonal changes in the night sky observed from different latitudes. It also highlights the importance of an observer’s geographic location in determining which stars are visible at any given time.
For a more detailed exploration of this topic, you can refer to the University of Nebraska–Lincoln’s Astronomy Interactives, which offer interactive exercises on the motion of the sky.