How do Huck and Jim explain the stars?The Adventure of Huckleberry Finn by Mark Twain

In Chapter 12, Huck describes his and Jim's life on the
raft,

We
catched fish, and talked, and we took a swim now and then to keep off sleepiness. It was
kind of solemn drifting down the big, still river, laying on our backs, looking up at
the stars, and we didn't ever feel like talking loud, and it warn't often that we
laughed--only a little kind of a low chuckle.  We had mighty good weather, as a general
thing, and nothing ever happened to us at all--that night, nor the next, nor the
next.

In another passage from
Chapter 18, Huck continues his reflection on the
raft:

 We said
there warn't no home like a raft, after all.  Other places do seem so cramped up and
smothery, but a raft don't. You feel mighty free and easy and comfortable on a
raft.

As they travel down the
Mississippi river, Huck and Jim enjoy their idyllic life on the river, that refuge from
the evils of society.  While on the raft, the world is good, there is no inequality
between Jim and Huck, there are no conflicts with Pa or others.  Life on the raft is a
solemn experience; it would seem disrespectful to talk loudly on this sanctuary from
civilization with its corrupt institutions.  In the natural world of the river in the
open air with only the stars as their ceiling, the souls of Huck and Jim can
expand--they look to the heavens as an expression of this feeling of expansion and
delight in nature.