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The star-effect may be also caused by the inclusions of hematite. In black star sapphire hematite needles formed parallel to the faces of the second order prism produce asterism. Some star sapphires from Thailand contain both hematite and rutile needles forming a 12-ray star. [3] Star-stones were formerly regarded with much superstition. [1]
In Greek antiquity the ideas of celestial spheres and rings first appeared in the cosmology of Anaximander in the early 6th century BC. [7] In his cosmology both the Sun and Moon are circular open vents in tubular rings of fire enclosed in tubes of condensed air; these rings constitute the rims of rotating chariot-like wheels pivoting on the Earth at their centre.
The following is a list of stars with resolved images, that is, stars whose images have been resolved beyond a point source. Aside from the Sun , observed from Earth , stars are exceedingly small in apparent size, requiring the use of special high-resolution equipment and techniques to image.
Jost Bürgi and Antonius Eisenhoit: Armillary sphere with astronomical clock, made in 1585 in Kassel, now at Nordiska Museet in Stockholm. A armillary sphere (variations are known as spherical astrolabe, armilla, or armil) is a model of objects in the sky (on the celestial sphere), consisting of a spherical framework of rings, centered on Earth or the Sun, that represent lines of celestial ...
The Nebra sky disc, c. 1800–1600 BC. The Nebra sky disc (German: Himmelsscheibe von Nebra, pronounced [ˈhɪml̩sˌʃaɪbə fɔn ˈneːbra]) is a bronze disc of around 30 cm (12 in) diameter and a weight of 2.2 kg (4.9 lb), having a blue-green patina and inlaid with gold symbols.
Rutile is an oxide mineral composed of titanium dioxide (TiO 2), the most common natural form of TiO 2. Rarer polymorphs of TiO 2 are known, including anatase , akaogiite , and brookite . Rutile has one of the highest refractive indices at visible wavelengths of any known crystal and also exhibits a particularly large birefringence and high ...
Both stars share similar physical characteristics to the Sun, [14] so they are considered solar analogs. Their stellar classification is nearly identical to that of the Sun. ζ 1 has 94% of the Sun's mass and 90% of the Sun's radius . ζ 2 is slightly larger and more luminous than ζ 1 , with 96% of the Sun's mass and 98% of the Sun's radius. [ 6 ]
The declination ring is moveable, and rotates on pivots set in the meridian ring. An imaginary line connecting these pivots is parallel to the Earth's axis. The declination "ring" of the traveller's sundial above is not a ring at all, but an oblong loop with a slider for setting the season.