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In astronomy, coordinate systems are used for specifying positions of celestial objects (satellites, planets, stars, galaxies, etc.) relative to a given reference frame, based on physical reference points available to a situated observer (e.g. the true horizon and north to an observer on Earth's surface). [1]
The star Polaris, often called either the "Pole Star" or the "North Star", is treated specially due to its proximity to the north celestial pole. When navigating in the Northern Hemisphere , a simple and quick technique can be used with Polaris to determine the observers latitude or, for larger maritime vessels can be used to calculate any ...
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. On Earth , a pole star would lie directly overhead when viewed from the North or the South Pole .
Hypergiant star currently undergoing a great dimming event HR 5171 Aa 4.1 ± 0.8: 1060–1160 [37] 11 740 ± 1630: Very Large Telescope – VLTI/PIONIER [38] 2014: Eclipsing and potential contact binary yellow hypergiant: WOH G64: 800 [39] ca. 160 000: Very Large Telescope – VLTI/GRAVITY [40] 2024 Star is in the Large Magellanic Cloud.
Star trail image of the north polar region. A digital camera with a standard lens is mounted on the telescope and pointed at the celestial pole. Exposure is set at "B" (Bulb) and an image is taken while the camera is slowly turned around the polar axis. [7] This yields a kind of star-trail image.
The position of the star lies less than 1° away from the north celestial pole, making it the current northern pole star. The stable position of the star in the Northern Sky makes it useful for navigation. [16] As the closest Cepheid variable its distance is used as part of the cosmic distance ladder.
A slow motion of Earth's axis, precession, causes a slow, continuous turning of the coordinate system westward about the poles of the ecliptic, completing one circuit in about 26,000 years. Superimposed on this is a smaller motion of the ecliptic , and a small oscillation of the Earth's axis, nutation .
In the case of observed visual binary stars, it is defined as the angular offset of the secondary star from the primary relative to the north celestial pole. As the example illustrates, if one were observing a hypothetical binary star with a PA of 30°, that means an imaginary line in the eyepiece drawn from the north celestial pole to the ...