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The outermost part of the stellar atmosphere, or upper stellar atmosphere, is the corona, a tenuous plasma which has a temperature above one million Kelvin. [6] While all stars on the main sequence feature transition regions and coronae, not all evolved stars do so. It seems that only some giants, and very few supergiants, possess coronae.
The ancient Greeks assumed the literal truth of stars attached to a celestial sphere, revolving about the Earth in one day, and a fixed Earth. [9] The Eudoxan planetary model , on which the Aristotelian and Ptolemaic models were based, was the first geometric explanation for the "wandering" of the classical planets . [ 10 ]
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.
Earth's rotation axis moves with respect to the fixed stars (inertial space); the components of this motion are precession and nutation. It also moves with respect to Earth's crust; this is called polar motion. Precession is a rotation of Earth's rotation axis, caused primarily by external torques from the gravity of the Sun, Moon and other bodies.
A stellar atmosphere is the outer region of a star, which includes the layers above the opaque photosphere; stars of low temperature might have outer atmospheres containing compound molecules. The atmosphere of Earth is composed of nitrogen (78%), oxygen (21%), argon (0.9%), carbon dioxide (0.04%) and trace gases. [2]
The Astronomical Almanac describes several different types of aberration, arising from differing components of the Earth's and observed object's motion: Stellar aberration: "The apparent angular displacement of the observed position of a celestial body resulting from the motion of the observer. Stellar aberration is divided into diurnal, annual ...
The heliosphere is the magnetosphere, astrosphere, and outermost atmospheric layer of the Sun.It takes the shape of a vast, tailed bubble-like region of space.In plasma physics terms, it is the cavity formed by the Sun in the surrounding interstellar medium.
A celestial map by the Dutch cartographer Frederik de Wit, 1670. A star chart is a celestial map of the night sky with astronomical objects laid out on a grid system. They are used to identify and locate constellations, stars, nebulae, galaxies, and planets. [1] They have been used for human navigation since time immemorial. [2]