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As viewed from the Earth, the ring of the Sun was highest, that of the Moon was lower, and the sphere of the stars was lowest. Following Anaximander, his pupil Anaximenes (c. 585 – c. 528/4) held that the stars, Sun, Moon, and planets are all made of fire.
At their intersections with the celestial sphere, these form the celestial equator, the north and south celestial poles, and the ecliptic, respectively. [8] As the celestial sphere is considered arbitrary or infinite in radius, all observers see the celestial equator, celestial poles, and ecliptic at the same place against the background stars.
Beyond the planets was the sphere of fixed stars, also motionless. This system presented two more unique ideas in addition to being heliocentric: the Earth rotated daily to create day, night, and the perceived motions of the other heavenly bodies, and the sphere of fixed stars at its boundary were immensely distant from its center. [9]
The term night sky refers to the sky as seen at night. The term is usually associated with skygazing and astronomy, with reference to views of celestial bodies such as stars, the Moon, and planets that become visible on a clear night after the Sun has set. Natural light sources in a night sky include moonlight, starlight, and airglow, depending ...
The southern celestial hemisphere, also called the Southern Sky, is the southern half of the celestial sphere; that is, it lies south of the celestial equator. This arbitrary sphere, on which seemingly fixed stars form constellations, appears to rotate westward around a polar axis as the Earth rotates. At all times, the entire Southern Sky is ...
Bayer's naming convention has been in use since 1603, and consists of a Greek letter combined with the possessive form of the star's constellation. [1] Both names are shown for each star in the tables and charts below. Each star's approximate position on the celestial sphere is given using the equatorial coordinate system.
This star is relatively close at only 25 light-years (7.7 parsecs) from the Sun, and one of the most luminous stars in the Sun's neighborhood. It is the fifth-brightest star in the night sky, and the second-brightest star in the northern celestial hemisphere, after Arcturus.
The host star itself is a magnitude 4.5 star of type F7V, 15.6 parsecs from Earth. It has a mass of 1.3 M ☉ and a radius of 1.331 solar radii (R ☉); a companion, GJ527B, orbits at a distance of 240 AU. Tau Boötis b, the sole planet discovered in the system, orbits at a distance of 0.046 AU every 3.31 days.