C: differences between char pointer and array

Consider:

char amessage[] = "now is the time";
char *pmessage = "now is the time";

I read from The C Programming Language, 2nd Edition that the above two statements don't do the same thing.

I always thought that an array is an convenient way to manipulate pointers to store some data, but this is clearly not the case... What are the "non-trivial" differences between arrays and pointers in C?