Final answer:
The altitude of Polaris at a given location is approximately equal to the observer's latitude. You can measure its altitude using a protractor or the width of a fist at arm's length to gauge latitude. However, this method is not applicable in the Southern Hemisphere as Polaris is not visible there.
Step-by-step explanation:
The rule for determining the altitude of Polaris, commonly known as the North Star, is relatively simple: The star appears at an altitude above the horizon that is approximately equal to the observer's latitude. For example, if you are standing at the equator (0° latitude), Polaris will be at the horizon, barely visible. As you move northward, its altitude increases such that if you stood at the North Pole (90° latitude), Polaris would be directly overhead.
Practically, to measure the altitude of Polaris, one can use a protractor or even one's fist at arm's length, where each fist-width approximates 10° of altitude. By measuring how many fist-widths Polaris is above the horizon, an observer can estimate their latitude. However, this method can't be used in the Southern Hemisphere, where Polaris is not visible.
The importance of Polaris for navigation is longstanding because, unlike other stars that move across the sky, Polaris remains fixed in the north due to its position near the north celestial pole, around which the Earth rotates. While Polaris is not the brightest star in the sky, that title goes to Sirius, it is a critical tool for orientation in the northern hemisphere.
Over time, due to the precession of the Earth's axis, the identity of the North Star changes. Currently, Polaris holds this title, but in about 14,000 years, the star Vega will take its place as the North Star.