How do you get a shiny Articuno in Pokemon FireRed?

Shiny Articuno is just like any other shiny pokemon you have a 1 out of 8000 chance to make it appear and since Articuno is part of the map screen rather than a Random Encounter you will need to Save your game before trying to capture it then press A to fight it if it's not shiny reset the game and try again each time you open your file you have another chance at Articuno being Shiny.