Space Day was created by Lockheed Martin Corporation in 1997. They even have a Space Day Kit on their site to help you celebrate the day. The goal was to motivate the youth of America to study math and science. This day was originally established as a one day event. An exciting topic of interest to millions, Space Day became an annual event.
There are a number of other Space Days that are held on by scientific groups and organizations interested in the subject of space. It focuses on celebrating the extraordinary achievements, benefits, and opportunities in the exploration and use of space.
I think most of us have always been fascinated by space. I am old enough to remember watching TV when we landed on the moon. It was an amazing event and even though I was pretty young at the time, I realized how important it was to everyone. From that time on, I have followed our space exploration programs.
I also check out the Astronomy Picture of the Day, everyday! I highly recommend this. There are many amazing pictures on this site.
This day was expanded to International Space Day in 2001 by John Glenn.