you're gettin practically the same advice on each reply. Pleae try the ground, ensure connections are correct, tap the starter with a hammer...solenoid could be sticking, and report back.
Just because the battery is 5 mons old, doesn't mean it is still good. Put a charger on it. Or, jump it with another vehicle and let it run. PUt a volt meter on it when it does run and see what the alt puts out, both at the alt bolt (red wire) and at the battery.
You are correct, a '79 is one of the best vehicle to learn everything on. No computers, not too complex, well, except for all the smog vacuum lines and such.