The North Star, also known as Polaris, has been historically significant in helping humans determine the Earth's shape. The use of the North Star as evidence of Earth's roundness stems from observations of its position in the night sky as one travels from different latitudes.
The North Star appears relatively fixed in the northern celestial hemisphere, very close to the direction of the Earth's North Pole. This means that as you move northward from the equator, the North Star appears higher in the sky, while as you move southward from the equator, it appears lower in the sky or even disappears below the horizon.
In the ancient times, people noticed that as they traveled farther north, they could see the North Star at higher angles above the horizon. This observation suggested that they were getting closer to the North Pole. Likewise, sailors at sea noticed that the height of the North Star above the horizon changed depending on their latitude. These observations were consistent with the idea that the Earth is curved rather than flat.
To further illustrate this, let's consider an example. If you were to travel from the equator towards the North Pole, the North Star would appear to rise higher in the sky as you move northward. At the equator, it would be very close to the horizon, but as you move closer to the North Pole, it would appear nearly overhead. This change in the North Star's position is consistent with the Earth's curved surface.
These observations, along with other evidence gathered over centuries, helped confirm the spherical shape of the Earth. The use of the North Star was just one piece of the puzzle in understanding the Earth's roundness, but it provided a useful and observable phenomenon that supported the idea of a spherical Earth.