Question

How can we proof that the earth is spherical with the help of pole star

Answer 1

Pole star or polar star refers to a star, preferably bright, closely aligned to the axis of rotation of an astronomical object. This is most commonly used for stars close to the north and south celestial poles of the Earth. The name is frequently applied to Polaris in the constellation Ursa Minor, acknowledging its property (extant since the 10th century) of being the naked-eye star closest to the Earth's north celestial pole. The name Polaris, introduced in the 18th century, is shortened from New Latinstella polaris, meaning "pole star". Polaris is also known as Lodestar, Guiding Star, or North Star from its property of remaining in a fixed position throughout the course of the night and its use in celestial navigation. It is a dependable, though inexact, indicator of the direction toward the geographic north pole; it is virtually fixed, and its angle of elevation can also be used to determine latitude. The south celestial pole lacks a bright star like Polaris to mark its position. At present, the naked-eye star nearest to the celestial south pole is the faint Sigma Octantis, sometimes called the South Star.

The identity of the pole stars gradually changes over time because the celestial poles exhibit a slow continuous drift through the star field. The primary reason for this is the precession of Earth's rotational axis, which causes its orientation to change over time. Precession causes the celestial poles to trace out circles on the celestial sphere approximately once every 26,000 years, passing close to different naked-eye stars at different times (with an additional slight shift due to the proper motion of the stars