Blender material issue while snapping two objects snaps together

Question

This is two half-sphere snap to each other by the center line. I am working on a modeling project which run into this problem.

I want to make it like a whole sphere while render it out, but it like this

The vertex at the center line are perfectly aligned.

And I would like to keep it two objects.

Is there any way to make it like one single object but without that center line?

Answer 1

I think there are two reasons here for discontinuous smooth shading.

1. The normals are flipped on the right half ... CtrlF > F, Flip normals
2. The normals haven't got anything to interpolate to over the edges of the hemispheres.

To fix (2), retain an intact version of the sphere as a form, same topology, same location, and transfer the normals from it to the 2 halves, by giving them Data Transfer modifiers, with the intact sphere as target, and the settings shown. You will have to set 'Autosmooth' on the hemispheres in their data tabs.