How could Luke destroy the Death Star?

Question

In Star Wars movie, Luke blow up the death star by flying really close to the surface at high speed and shooting a missile straight down.

From what I understand it has to be at 45° before the top of the hole to shoot, like this:

 <=L=>mm
         m
           m
            m 
 ----------|m|---------------
           |m|
           |m|

Where m is the trajectory used by the missile.

Is there any explanation on how can the missile turn in such a steep way, and why couldn't it be fired from somewhere else, since the missiles seems to have extra high maneuverability ?

Answer 1

Space magic.... I mean the force.

It was Obi's force ghost telling him to not use instruments and only use the force that allowed the shot to be on target.