Question

What is the exact distance from Earth to Neptune?

Answer 1

It is never “exact” nor constant.

Explanation:

The distance from one planet to another is constantly shifting because both bodies are moving through space. When Neptune and Earth line up on the same side of the sun, at their closest, they are only 2.7 billion miles (4.3 billon kilometers) apart. But when the planets are on opposite sides of the sun, they can put as many as 2.9 billion miles (4.7 billion km) between them.
http://www.space.com/18923-neptune-distance.html