We all know what Doc Brown said in the first movie. "I need a nuclear reaction to generate the 1.21 gigawatts of electricity I need". But he pronounced gigawatts as if it were spelled with a "j", as in jigawatts (or jigowatts). Being an electrical engineer, I had heard the prefix "Giga" pronounced many times before, but always with the hard "g" sound, as in gigabyte.
I always figured that the word "Jigawatt" was made up just for the movie and meant to sound like a really large amount. It wasn't unit I started researching this flux capacitor replica project that I stumbled across a few references to the actual term. It turns out that the original pronunciation of "Giga" was with the "j" sound (really a soft "g").
UPDATE (4/20/13). Merriam-Webster has pulled their alternate pronunciation for gigawatt. Now they only have the "J" sounding version, as used in BTTF. I don't know if they have changed their minds on the alternate or Doc Brown went back in time to correct it. The two pronunciation links above still work though.
I am certainly happy that they used the original, older sounding pronunciation of the word since the story involved time travel and Doc Brown conceived of the flux capacitor on November 5th in 1955 after slipping and hitting his head on the toilet. Ironically, most references point to the early 1960's as the first time the term was used. That's okay at the start of the film as it's set in 1985, but in 1955, the younger Doc Brown should have said "1.21 gigawatts? What's a gigawatt Marty?
The saying over the years has taken on a life of its own. I've heard people say it without even knowing where it came from. What's even more fun is the debate that follows on whether a gigawatt is an actual term. People would rather debate the pronunciation of the word then ponder the possibilities of time travel. Here's hoping for a Back to the Future 4. Let's make it a reality while we still can.
So, how much is 1.21 gigawatt you ask? Well, a gigawatt is equal to one billion (10 9) watts or 1 gigawatt = 1000 megawatts. If your typical 100 wattt lightbulb (at least what used to be typical before they outlawed them here in the US) were powered for 1 hour, that would be 100 Watt-hours. 1.21 gigawatts would be able to light over 12 million 100 Watt light bulbs for an hour. 1.21 gigawatt is also equivalent to 1,621,400 horse power.