That's right. Other basics of it are like this. From the bottom of a surface and up you start out with the grounds color, normally green or brown. Make it the lightest brown at the bottom and work up, making the brown darker and darker until you get to the horizon line (HL) which should be near black. Now start with the sky, and this starts out pure white turn goes to the lightest color of the sky-normally blue. Get progressively darker as you go up. That's it basically, add a glint for the sun maybe and edge highlight in white on places. The HL is shaped differently depending on the type of surface. On a shield it would be curved extreme on the edges. On a cylinder no matter what it must go across the x axis, even if this make no sense in relation to the actual horizon. The tilt of the surface determines how much sky or earth is shown. That's it in a nut shell. A fun effect to paint, looks exceptional on multiple chrome surfaces in close proximity, like a robot.
Oh, also sky earth doesn't have to be done with steel. You can do it with gold, blue, whatever color. Just keep the same principles but substitute the brown and blue with the appropriate colors. A reflective gold is sometimes appropriate rather than standard gold NMM for example.