fix possible range of solar apparent magnitude

Unsure where I got (-1.5, 1.5)
Autorelease all the objects

If consumers of this need the objects for longer, they can retain
them for as long as needed, but I don't want to leak memory.

ARC? Neat idea, but sometimes it's fun to manage your own memory.
Use color to highlight solar attributes

This should be a sliding scale from GREEN (very close to target star)
to RED (very far away from target star).

For now, the target star is Sol, because it's easier, conceptually to think
about people colonizing stars that are roughly humanoid, but there's no
reason why this couldn't change in the future.

My only regret here is that I did not use bindings for these values. I can
foresee a future where the mass, radius, temperature, etc of these objects
can vary at run time because of simulated events, and I'll definitely want
to use bindings more often.

Also having an internal discussion over whether or not to use mouse over
tooltips to describe these attributes in more detail, but I don't think
that's strictly necessary.