Widely considered one of the best science fiction movies ever made, this year Close Encounters of the Third Kind celebrates its 40th anniversary. The Steven Spielberg film was a major factor in sci-fi films returning to popularity, going on to inspire others in years following, including one of Spielberg's most popular films of all time, E.T. The Extra-Terrestrial.

Close Encounters of the Third Kind followed electrical lineman Roy Neary (Richard Dreyfuss), who has a close encounter with a UFO while inspecting a series of power outages. Following the incident Neary becomes obsessed with UFOs and a mysterious mountain-like image. Eventually Neary figures out what the image is, and the film culminates in an encounter that will forever change humankind. Take a look at the film's remastered trailer below:

Close Encounters was one of the most successful movies of 1977, and its legacy can still be felt in cinema today. To celebrate the 40th anniversary of Close Encounters of the Third Kind, a 4K restoration of Spielberg's director's cut is headed to cinemas for a one-week rerelease beginning September 1. And to prepare you for this cinematic marvel, here are six facts you may not know about Close Encounters of the Third Kind:

1. A UFO Expert Worked On It

[Credit: Columbia Pictures]
[Credit: Columbia Pictures]

Believe it or not, Close Encounters of the Third Kind's technical advisor was Dr. J Allen Hynek, "the world's foremost authority on unidentified flying objects." The North Western University professor was the founder of the Center for UFO Studies and was the scientific advisor for three UFO studies performed by the U.S. Air Force from 1947 until 1969. Hynek's 1972 book The UFO Experience: A Scientific Inquiry detailed his "Close Encounter" scale that gave the film its name.

Aside from being a technical advisor, Hynek also had a cameo appearance at the end of the film. The professor can be seen as pushing his way through a crowd of scientists to get a better look at the aliens and then putting a pipe in his mouth.

2. It's Preserved In The National Film Registry

'Close Encounters of the Third Kind' [Credit: Columbia Pictures]
'Close Encounters of the Third Kind' [Credit: Columbia Pictures]

In 2007 — the film's 30th anniversary year — Close Encounters was considered to be "culturally, historically, or aesthetically significant" by the United States Library of Congress. It was then added to the National Film Registry for preservation, which now has 700 significant films preserved.

3. George Lucas Was Convinced It Would Perform Better Than Star Wars

'Star Wars' [Credit: Lucasfilm/20th Century Fox]
'Star Wars' [Credit: Lucasfilm/20th Century Fox]

While Close Encounters of the Third Kind premiered in November 1977 and quickly became an enormous success, earlier in the year Star Wars (a.k.a Star Wars: Episode IV — A New Hope) had became the unexpected blockbuster of the summer season. In fact Star Wars was such a surprise hit that not even its director, George Lucas, saw it coming — but Steven Spielberg did.

Before the release of both movies, Lucas visited the set of Close Encounters in Mobile, Alabama and became certain that his film would flop and that Spielberg's film would be a hit. Lucas was so convinced that the rival film would perform better than he offered Spielberg 2.5% of Star Wars' profits in return for 2.5% of Close Encounters'. Spielberg took the gamble and although Close Encounters still managed impressive box office results — over $303 million worldwide — more than four decades later he's still profiting from the success of Lucas's franchise.

4. Spielberg Didn't Love The Initial Release

It's worth noting that the upcoming rerelease of Close Encounters is the director's cut, given that Spielberg himself has been pretty vocal on the fact that he didn't love the film's initial release.

Due to pressure from Columbia Pictures — who were relying on the film to solve financial issues — Spielberg was forced to finish the movie in time for a late 1977 release, rather than the mid-1978 release he wanted. Following the massive success of the film, Spielberg went back to Columbia and asked for financial backing in order to finish the film how he envisioned for the 1980 Special Edition. Columbia agreed to give him the budget on the condition that his reshoots showed the inside of the mother-ship, which would provide a great hook for a marketing campaign. Spielberg compromised, and added the shot of Roy Neary entering the mother-ship, a sequence he has later said he "never should have done" as he believes the inside of the ship "should have always been kept a mystery." The mothership scenes were later deleted for the 1988 Collectors Edition rerelease, which Spielberg considers his definitive version.

5. The Famous Five-Note Tune Was Picked From Hundreds Of Versions

The five-note melody used in the film to communicate with the aliens was picked from hundreds of versions that composer John Williams created for Steven Spielberg to choose from out of the 134,000 possible combinations. Aside from being used as communication between humans and aliens, the notes can also be heard as Roy Neary is about to enter the mothership at the end of the film.

6. Despite Being Just A Kid, Cary Guffey Was A Pro

'Close Encounters of the Third Kind' [Credit: Columbia Pictures]
'Close Encounters of the Third Kind' [Credit: Columbia Pictures]

Although he's since retired from acting, Cary Guffey — who played Barry Guiler in the film — was so impressive on the set that he earned the nickname "one-take Cary" for his ability to nail a scene in just one take. Much of this was down to Spielberg's knack at getting the best from the young star using toys and costumes to elicit the response needed for the scene. Guffey's parents also helped their son learn what few lines he did have by reading his scenes and having him memorize it. This resulted in a funny moment during Guffey's one scene with Richard Dreyfuss when the veteran actor flubbed his line and the young tot called him out on it.