Springtime on Neptune: Increased Brightness Shows Seasonal Change
The semi-major axis of Neptune's orbit about the Sun is 30.06 Astronomical Units (A.U.) or roughly 4.5 billion km.
The planet has a diameter of roughly 30,800 miles (49,600 km) at the equator.
These data are from HST proposals 6650, 7324 and 9393. The science team includes: L. A. Sromovsky, P. M. Fry, and S. S. Limaye (University of Wisconsin-Madison's Space Science and Engineering Center), and K. Baines (JPL).
F467M (Strömgren b), F673N ([S II]), and F850LP (9650Å)
NASA, L. Sromovsky, and P. Fry (University of Wisconsin-Madison)