Astronomy and astrology in Middle-Earth?

[The Might]

Well I see we have reached quite a conclusion, so I'll add something I just thought of and that although is not truly this thread's topic is also close to it.

Now, we know that Aragorn went

even into the far countries of Rhûn and Harad where the stars are strange.

Clearly it seems that Arda also had two totally distinct hemispheres with different stars on the sky.
The thing in Tolkien's works is that all is quite North-centred and pretty much nothing is said about the South.

In the North stars are used to signal something, for example the Valacirca to be a warning for Melkor and his followers.

My question is simple...was there a reason for stars with a meaning in the South and if so is there any mention of this?