Circles of Right Ascension: Using Imaginary Lines to Measure Position of Stars and Planets in the Sky

As the celestial bodies sweep from east to west across the sky what lines are they tracing out

Lines of declination

As celestial bodies, such as stars, planets, and the moon, appear to move across the sky from east to west, they are tracing out imaginary lines called circles of right ascension. These circles are similar to the lines of longitude on Earth and are used to measure the position of celestial objects in the sky. Circles of right ascension are defined based on the position of the vernal equinox, which is the point on the celestial sphere where the ecliptic (the apparent path of the Sun across the sky) intersects with the celestial equator (the projection of the Earth’s equator onto the celestial sphere). As the celestial bodies move across the sky, they appear to move along circles of right ascension that are determined by their positions relative to the vernal equinox.

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