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The two smaller companions are Polaris B, a 1.39 M ☉ F3 main-sequence star orbiting at a distance of 2,400 astronomical units (AU), [17] and Polaris Ab (or P), a very close F6 main-sequence star with a mass of 1.26 M ☉. [3]
A special reticle is used to align the mount with Polaris (or a group of stars near the polar region) in the Southern Hemisphere. While primitive polariscopes originally needed the careful adjustment of the mount to match the time of year and day, this process can be simplified using computer apps that calculate the correct position of the reticle.
Popular choices of pole and equator are the older B1950 and the modern J2000 systems, but a pole and equator "of date" can also be used, meaning one appropriate to the date under consideration, such as when a measurement of the position of a planet or spacecraft is made.
The modern method consists of numerical integration in 3-dimensional space. One starts with a high accuracy value for the position (x, y, z) and the velocity (v x, v y, v z) for each of the bodies involved. When also the mass of each body is known, the acceleration (a x, a y, a z) can be calculated from Newton's Law of Gravitation. Each body ...
A diagram of a typical nautical sextant, a tool used in celestial navigation to measure the angle between two objects viewed by means of its optical sight. Celestial navigation, also known as astronavigation, is the practice of position fixing using stars and other celestial bodies that enables a navigator to accurately determine their actual current physical position in space or on the ...
Northern Hemisphere circumpolar stars around Polaris, with a long-exposure producing a star trail photo. A pole star is a visible star that is approximately aligned with the axis of rotation of an astronomical body; that is, a star whose apparent position is close to one of the celestial poles.
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Polaris (within 1° of the pole) is the nearly stationary bright star just to the right of center in this star trail photo. The north celestial pole currently is within one degree of the bright star Polaris (named from the Latin stella polaris , meaning " pole star ").