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In astronomy, the fixed stars (Latin: stellae fixae) are the luminary points, mainly stars, that appear not to move relative to one another against the darkness of the night sky in the background. This is in contrast to those lights visible to naked eye , namely planets and comets , that appear to move slowly among those "fixed" stars.
(1 AU and 1 parsec are not to scale, 1 parsec = ~206265 AU) Stellar parallax is the apparent shift of position of any nearby star (or other object) against the background of distant stars. By extension, it is a method for determining the distance to the star through trigonometry, the stellar parallax method.
Stars slowly lose mass by the emission of a stellar wind from the photosphere. The star's magnetic field exerts a torque on the ejected matter, resulting in a steady transfer of angular momentum away from the star. Stars with a rate of rotation greater than 15 km/s also exhibit more rapid mass loss, and consequently a faster rate of rotation decay.
Early astronomers recognized a difference between "fixed stars", whose position on the celestial sphere does not change, and "wandering stars" , which move noticeably relative to the fixed stars over days or weeks. [6] Many ancient astronomers believed that the stars were permanently affixed to a heavenly sphere and that they were immutable.
In reality, stars orbit the center of their galaxy. Stars with an orbit retrograde relative to a disk galaxy's general rotation are more likely to be found in the galactic halo than in the galactic disk. The Milky Way's outer halo has many globular clusters with a retrograde orbit [38] and with a retrograde or zero rotation. [39]
For most stars seen in the sky, the observed proper motions are small and unremarkable. Such stars are often either faint or are significantly distant, have changes of below 0.01″ per year, and do not appear to move appreciably over many millennia. A few do have significant motions, and are usually called high-proper motion stars.
As stars move through an arm, the space velocity of each stellar system is modified by the gravitational force of the local higher density. Also the newly created stars do not remain forever fixed in the position within the spiral arms, where the average space velocity returns to normal after the stars depart on the other side of the arm. [29]
The rotational/orbital speeds of galaxies/stars do not follow the rules found in other orbital systems such as stars/planets and planets/moons that have most of their mass at the centre. Stars revolve around their galaxy's centre at equal or increasing speed over a large range of distances.