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In 3000 BC, the faint star Thuban in the constellation Draco was the North Star, aligning within 0.1° distance from the celestial pole, the closest of any of the visible pole stars. [ 7 ] [ 8 ] However, at magnitude 3.67 (fourth magnitude) it is only one-fifth as bright as Polaris, and today it is invisible in light-polluted urban skies.
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.
Star 3rd century BC — 1609 380 Earth radii (very inaccurate, true=16000 Earth radii) Aristarchus of Samos made a measurement of the distance of the Sun from the Earth in relation to the distance of the Moon from the Earth. The distance to the Moon was described in Earth radii (20, also inaccurate).
Vega was the northern pole star around 12,000 BCE and will be so again around the year 13,727, when its declination will be +86° 14′. [19] Vega was the first star other than the Sun to have its image and spectrum photographed. [20] [21] It was one of the first stars whose distance was estimated through parallax measurements.
This number is likely much higher, due to the sheer number of stars needed to be surveyed; a star approaching the Solar System 10 million years ago, moving at a typical Sun-relative 20–200 kilometers per second, would be 600–6,000 light-years from the Sun at present day, with millions of stars closer to the Sun.
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Sigma Octantis is a solitary [9] star in the Octans constellation that forms the pole star of the Southern Hemisphere.Its name is also written as σ Octantis, abbreviated as Sigma Oct or σ Oct, and it is officially named Polaris Australis (/ p oʊ ˈ l ɛər ɪ s ɔː ˈ s t r eɪ l ɪ s /). [10]
Alpha Cephei (α Cephei, abbreviated Alpha Cep, α Cep), officially named Alderamin / æ l ˈ d ɛr ə m ɪ n /, [10] [11] is a second magnitude star in the constellation of Cepheus near the northern pole. The star is relatively close to Earth at 49 light years (ly) and drifting closer with a heliocentric radial velocity of about −16 km/s.