Asteroid Day was selected to be on the day of the anniversary of the 1908 Siberian Tunguska event, which is the largest asteroid impact on Earth in recent history. The purpose of this day is to help people learn about asteroids (of course!) and what, if anything, we can do to protect our planet from them. So, grabbed your loved ones and get online to learn all about this day and what you can do to participate!
You can read all about it at http://www.asteroidday.org/