It's finally here. Wednesday is Oct. 21, 2015 -- the day Marty McFly time-traveled to in the 1989 movie "Back to the Future Part II" -- and what better way to celebrate than by slipping some of your favorite phrases from the film into everyday conversation? On this momentous occasion, jokingly saying "that's heavy" is not enough. 

The original "Back to the Future" premiered July 3, 1985. Starring Michael J. Fox and Christopher Lloyd, the film follows high school student Marty as he takes scientist Doc Brown's time machine to the 1950s and then must fight his way back to the present, awkwardly encountering younger versions of his mother and father in the process. The Oct. 21 date is actually at the center of the movie's sequel, where -- you guessed it -- Marty travels to the future and inadvertently messes up the present. If all of that confuses you, just skip the third film (actually, you should do that anyway).

The series attracted a cult following that propelled Back to the Future Day to fame. Play along by remembering these quotes from the films, collected from IMDb and Wikiquote:

"Great Scott!" -- Doc

"Last night, Darth Vader came down from Planet Vulcan and told me that if I didn't take Lorraine out, that he'd melt my brain." -- George McFly

"Wait a minute. Wait a minute Doc, uh, are you telling me you built a time machine ... out of a DeLorean?" -- Marty McFly

"The way I see it, if you're going to build a time machine into a car, why not do it with some style?" -- Doc

"What the hell is a gigawatt?" -- Marty McFly

"Why don't you make like a tree and get out of here?" -- Biff Tannen

"Whoa, this is heavy." -- Marty McFly

"There's that word again: 'heavy.' Why are things so heavy in the future? Is there a problem with the Earth's gravitational pull?" -- Doc

"I'm your density. I mean, your destiny." -- George McFly

"I've never seen purple underwear before." -- Lorraine Baines

"Where are my pants?" -- Marty McFly

"Over there, on my hope chest." -- Lorraine Baines

"I'm sure that in 1985 plutonium is available at every corner drugstore, but in 1955 it's a little hard to come by." -- Doc

"Then tell me, future boy, who's President of the United States in 1985?" -- Doc

"Ronald Reagan." -- Marty McFly

"Ronald Reagan? The actor? Then who's vice president? Jerry Lewis? I suppose Jane Wyman is the first lady." -- Doc

"Roads? Where we're going we don't need roads." -- Doc