Blue Light Neptune Global Map from Hubble's OPAL Program (Dark Spot Closeup)
The semi-major axis of Neptune's orbit about the sun is 30.06 astronomical units (roughly 2.8 billion miles or 4.5 billion kilometers).
Neptune has a diameter of roughly 30,800 miles (49,600 kilometers) at the equator.
Data were provided by the HST proposal 14492: M.H. Wong (PI), I. de Pater, J. Tollefson, and K. de Kleer (UC Berkeley), H. Hammel (Space Science Institute), S. Cook (AMNH), R. Hueso and A. Sanchez-Lavega (University of the Basque Country, Spain), A. Simon (NASA/GSFC), M. Delcroix (French Astronomical Society, SAF), L. Sromovsky and P. Fry (University of Wisconsin, Madison), G. Orton (JPL), and C. Baranec (University of Hawaii, Manoa).
This image is a single, monochrome filter that isolated blue light (F467M) was used to record overall brightness. These brightness values were translated into a range of bluish hues. Such color "maps" can be useful in helping to distinguish subtly varying brightness in an image.