Star Wars Day is May 4th so you are probably wondering how you would build deflector shields in case the US government is worried about turtles on its former nuclear testing grounds and thinks your cows will harm the ecosystem and sends a Death Star after you.

You're in luck; not only are they scientifically feasible, the principle behind them is already used here on Earth.

If you're too young to have seen the original, and missed the flawed prequels, you needn't feel left out - in almost every science-fiction scenario, spaceships are protected by a shield defense system that deflects enemy laser fire. 

Death Star. Source: Wikipedia.
Link: University of Leicester.

How would you build one of those? You'd need a surrounding field of super-hot plasma, held in place by a magnetic field around the ship. The denser the plasma, the higher the frequency of electromagnetic wave - laser radiation - deflected.

The principle is already used in ‘over-the-horizon’ radio communications, used for decades in early warning RADAR systems and for long distance communications where satellite communications are not feasible.

Three fourth-year physics students from the University of Leicester tackled the problem of how to create this kind of deflector shield.  They also discovered one limitation.

They calculated that the magnet strength required is achievable, but would need a large power source that would restrict space in your ship. One major restriction would be that a shield designed to deflect light radiation would prevent any light reaching the pilot, leaving them effectively blind.

That's solvable, though. Set phasers for fun!

Citation: Joseph McGuire, Alexander Toohie, Alexandra Pohl, 'P6_11 Shields Up! The Physics of Star Wars', Physics Special Topics, North America, 12 8 12 2013.