What is the process of maintaining a constant internal environment called

It is called the homeostasis.

Homeostasis is the living organism's mechanism to maintain and sustain its internal environment at the level where it will suffice for them to survive. This process involves the pulling and pushing of delinquencies and extremities with an organism. 

The answer is atmosphere. there are four spheres of the earth: 1. geosphere (from greek word 'geo' = ground), 2. hydrosphere (from greek word 'hydro' = water), 3. biosphere (from greek word 'bio' = life), and 4. atmosphere (from greek word 'atmo' = air). a magnetosphere is a region of space around astronomical objects controlled by the magnetic field of that object. through the process of elimination, since lightning is present in the air, it can be found in the atmosphere.