You may be wondering, "What is the Golden Ratio?" Well, for a brief summary, Wikipedia defines the Golden Ratio as a ratio that occurs between two quantities if the sum of those two quantities is larger than the two quantities themselves.
You also may be wondering why, out of all days, did people choose June 18 to celebrate the Golden Ratio? Well, the Golden Ratio is represented by an irrational number that starts with 1.618, so someone rounded down and got 0.618 as the first few numbers.
Now that's an amazing holiday, right?
Well, what you may not know is that the Golden Ratio is used to great effect in many kinds of art (like movies) to create a more appealing and natural image. So, if you want an excuse to watch movies like Full Metal Jacket or There Will Be Blood, Golden Ratio Day would be a good time.