Question

How far away is the sun from neptune in AU?

Answer 1

Perihelion (nearest):4444.5 M km = 29.71 AU; aphelion farthest) :4545.7 M km = 30.39 AU; average of these: 4495.1 M km = 30.05 AU.: :

Explanation:

There is a notion that the average of perihelion and aphelion ( semi-major axis a) is the average distance, over one period of revolution. Actually, in mathematical exactitude, the average distance for an orbiter is semi-minor axis b = a`sqrt`( 1 `-` e^2 ), of the orbit. For Neptune, the eccentricity is 0.011257 and b = 4494.8 M km= 30.046 AU against a =30.052 AU.,
I think that International Astronomical Union ( IAU ) AU = 14957870.7 km is b for the orbit of the Earth.
Reference for distances: NASA Planetary Fact sheet,