Celestial sphere

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The Yird rotatin within a relatively smaa-diameter Yird-centered celestial sphere. Depictit here are starns (white), the ecliptic (reid), an lines o richt ascension an declination (green) o the equatorial coordinate seestem.

In astronomy an navigation, the celestial sphere is an imaginary sphere o arbitrarily lairge radius, concentric wi Yird. Aw objects in the observer's sky can be thoucht o as projectit upon the inside surface o the celestial sphere, as if it wur the unnerside o a dome or a hemispherical screen. The celestial sphere is a practical tuil for spherical astronomy, allaein observers tae plot poseetions o objects in the sky when thair distances are unkent or unimportant.