Constellations are groupings of stars as seen from Earth, and they don't have actual physical proximity in space. Neptune is in the constellation Aquarius, but that doesn't mean it's the closest to Neptune.

It's important to note that:

* Neptune is not "in" Aquarius. The constellation Aquarius is simply the patch of the sky where Neptune happens to appear from our vantage point on Earth.

* Distance in space is complex. While Aquarius is the constellation Neptune is "in" from our perspective, other constellations are closer to Neptune in terms of actual spatial distance.

So, there's no "closest" constellation to Neptune in a meaningful way. It's like asking what the closest constellation is to the sun, which doesn't really make sense because the sun is within our solar system, and constellations are distant star groupings.