Planetary shield

A planetary shield in Star Wars is a roughly-spherical shape that encompasses an entire planet, protecting it from orbital bombardment. Several references to planetary shielding technology and its effects are made throughout the Star Wars film-canon.

Star Wars IV: A New Hope

In perhaps the most spectacular demonstration of a planetary shield's power, the destruction of the planet Alderaan shows the 'breaking point' of a core-world's planetary shield. The Death Star I fires its planet destroying superlaser at Alderaan, a beam with a calculated energy of 1E38 J. This energy beam strikes the planetary shield, but the planet does not begin to sustain damage for another tenth of a second. This means that, before giving out, the shield was able to dissipate 1E38 J of energy for a ridiculously long period of time (0.1s).

Star Wars V: The Empire Strikes Back

In Star Wars V, the Rebel Alliance is able to utilize a planetary shield to protect them from the Imperial Star Destroyers' bombardment for some time during the Battle of Hoth.

Star Wars VI: Return of the Jedi

This establishes the range of the shield-net itself. A planetary shield generator is employed on the sanctuary moon of Endor, prior to the Battle of Endor. The resultant shield not only extends to the upper atmosphere of the moon, but all the way out into space to entirely encompass the Death Star II as well. Aboard Home One, during the briefing given to the pilots prior to the attack on the Death Star II, a holographic projection of the shield indicates that it does indeed reach out in a conical structure to surround the orbiting Death Star.

Further, in the novelization, it is shown that when a ship crashes into this planetary shield the resultant effect destroys the ship.