of all the visible objects in the celestial sphere, which one appears to move the least? why?
The object that appears to move the least in the celestial sphere is the star Polaris, also known as the North Star. Polaris is located very close to the celestial North Pole, and its position in the sky appears to be almost stationary throughout the night.
To understand why Polaris appears to move the least, we need to consider the rotation of the Earth on its axis. As the Earth spins, the celestial sphere appears to rotate, causing all celestial objects to appear to move across the sky from east to west.
However, the North Star is located almost directly above the Earth's North Pole, which means it is aligned with the axis of the Earth's rotation. Because of this alignment, when we observe Polaris from any location in the Northern Hemisphere, it appears to remain fixed in the sky while other stars revolve around it throughout the night.
The reason behind this is that as the Earth rotates, the North Star stays close to the same spot in the sky due to its alignment with the Earth's axis. Other stars appear to move in circular or arc-like paths around Polaris, as they are at different distances from the celestial pole.
It's important to note that while Polaris appears relatively fixed over the course of a night, it does have a very slow motion in the long term. This is because the Earth's axis undergoes a slow, gradual precession, causing the position of the North Star to shift over thousands of years. However, on the timescale of a human lifespan, Polaris appears to be the least moving celestial object in the night sky.