During a clear night, try to observe the Big Dipper 3–4 times at an interval of 2 to 3 hours. Also try to locate the Pole Star each time. Does the Big Dipper appear to move? Draw a rough sketch to illustrate this, mentioning the time in each case.
The Big Dipper appears to move across the night sky over several hours.
When observed at intervals of 2-3 hours, the Big Dipper changes its position relative to the horizon—it appears to rotate around the Pole Star.
However, the Pole Star remains stationary in the North direction throughout the night.
In a rough sketch, students should draw the Big Dipper's position at different times (e.g., 8 PM, 10 PM, 12 AM) showing how it moves in an arc around the stationary Pole Star.
This apparent motion occurs because Earth rotates on its axis, causing the stars to appear to move across the sky while the Pole Star, being aligned with Earth's axis, remains fixed.
Explanation
The chapter mentions on Page 5 that the Pole Star appears stationary in the North direction. The Big Dipper lies in the constellation Ursa Major. As Earth rotates on its axis (taking about 24 hours for one full rotation as mentioned on Page 10), the stars appear to move across the sky. The Pole Star remains stationary because it is aligned with Earth's rotational axis, while other stars and constellations like the Big Dipper appear to move in circular paths around it.
Solution Steps
The Big Dipper appears to move across the night sky over several hours.
When observed at intervals, the Big Dipper changes position relative to the horizon and appears to rotate around the Pole Star.
The Pole Star remains stationary in the North direction throughout the night.
This apparent motion occurs because Earth rotates on its axis, while the Pole Star is aligned with Earth's axis.