Polaris is the brightest star in the constellation Ursa Major. For observers in the Northern Hemisphere, it holds a special position. Located just half a degree off the Earth’s axis, Polaris appears to remain almost stationary directly above the North Pole as the Earth rotates through the day and night cycle.
In modern astronomy, this star is part of a group of seven stars, known as the seven brightest stars within the boundaries of the Ursa Major constellation in the Northern Hemisphere. Aside from these seven stars, the Ursa Major constellation contains many other stars.
Western astronomers have also assigned specific names to these stars. Once these stars were systematized on celestial maps, they received scientific names according to the constellation Ursa Major.
“Polaris” is a colloquial term referring to a group of stars that includes multiple stars.
Position of the 7 stars of Polaris bright in the sky.
Due to the spherical shape of the Earth, the position of Polaris relative to the horizon depends on the observer’s location. Specifically, the angle between the northern horizon and Polaris is equal to the observer’s latitude. For instance, from the equator (latitude 0), Polaris is located on the northern horizon. When moving to Houston, Texas (latitude 30), Polaris is 30 degrees above the horizon. At the North Pole, Polaris is 90 degrees above the horizon, meaning it is directly overhead the observer.
In the past, northern sailors measured the angle between the horizon and Polaris to determine their latitude. However, latitude alone is insufficient to pinpoint a location on the Earth’s surface. Thus, while many cultures successfully conducted maritime explorations using celestial observations, weather conditions, and ocean currents, the “longitude problem” remained a source of dread for sailors for many millennia.
Currently, there is no corresponding star to Polaris in the Southern Hemisphere. Moreover, Polaris is not a perfectly accurate indicator of the North Pole, as the Earth’s axis not only rotates in a 24-hour cycle but also moves in a conical motion. Consequently, the projection of the Earth’s axis in the sky describes a cyclical circle over 26,000 years. Thus, Polaris changes over time; 5,000 years ago, the Earth’s axis pointed towards the constellation Draco, and at that time, the star Thuban was considered the North Star. Similarly, in 12,000 years, the star Vega in the constellation Lyra will serve as the North Star.
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