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The solar circle is the orbital path of the Sun around the galactic center. Sometimes the term is used to mean an exact circle that approximates the Sun's orbit, and other times it is used to mean the Sun's actual orbit, which has a moderate eccentricity, moderately close to a circle. This distinction may be significant for some uses of the concept, but for other uses, it may be insignificant due to other contributors to ambiguity. For example, determination of the Sun's precise orbit is non-trivial and is subject to correction as methods improve, so useful precision of current determinations is limited.
The radius of this circle, i.e., the distance to the galactic center is termed the solar galactocentric distance which is currently estimated to be in the range of 7.6 to 8.7 kpc.
A common use of the term solar circle within astrophysics is to specify the region of the Milky Way closer to the galactic center than we are (within the solar circle) or further (beyond the solar circle).