When I apply the mirror modifier the object that is mirroring the other object is very far away from the original. This has me very confused.:confused:

The center of the mirroring is the origin/model center.

You need to have this origin/model center to be placed correctly.
By example i have this half sphere that i moved :

Notice the “brown/orange” point , it’s the origin/model center, in this situation if i use a mirror now, i will not be able to get the half sphere becoming a sphere because the origin that is the center of the mirroring symetry is far from my half sphere .


to fix that, in Edit Mode, i need to select those vertices that are located where i would want the axe of symetry to be :

Theni click on Mesh -> Snap -> Cursor to Selected.
That will move the 3D cursor where i need

Then, in Object Mode, click on the “Origin” button in the Object Tool panel to the right of your screen
and select “Origin to 3D Cursor”
It will move the Origin to the 3D cursor location, it will then be where i really need for the mirror to work the correct symetry i need

Using the mirror modifier will now give me the correct mirrored half sphere i need to complete the sphere.

Okay thank you.