The "Multi Atmos" atmosphere let you put atmosphere on one or more moons in addition to the planet.
First, select the "Multi Atmos" item in the atmosphere drop down
list box.
Then expand the atmosphere control stack. It contains four new atmosphere sub control stacks.
Now, imagine you want to put an atmosphere to the planet and also to
each of the four moons you added to your current world. For the planet,
you may use any valid atmophere. However, for the moons, you must use a
specially designed atmosphere. Currently only one of them exists: it is
the "VClouds Atmos" atmosphere.
But there is still a problem: You need to affect five atmospheres and
the "MultiAtmos" only support four of them. This is not a problem at
all. All you need to do is to put another "Multi Atmos" as one of the
subatmospheres. This gives you now support for seven atmospheres. In
case you need even more atmospheres, just add more "Multi Atmos"
atmospheres.
The above picture shows one of the possible configurations. There is no required order. The atmospheres are dynamically sorted to achieve the correct evaluation order during rendering.