I'm Chief Astronomer Derrick Pitts of the Franklin Institute Science Museum. I'll be joining Dr. Nese regularly as we present "Franklin Facts" and today, Halloween is a great day for me to start because of its strong astronomical roots. Besides being just a day to collect candy, Halloween is a special day we can use to mark the earth's travels around the sun.

Halloween began in Celtic Ireland as "All Hallows Eve" around the 5th century B.C. It was a time for the living to avoid being captured by the spirits of the dead. Astronomically speaking, October 31 falls almost halfway between the first days of autumn and winter. That makes Halloween what's called a "cross-quarter day" - a special seasonal day that falls halfway between two seasons. There are four throughout the year - the others are: Feb 2nd - Candlemas or Groundhog's Day, May 1 - May Day, and August 1 - Lammas.

So along with all the other ghostly symbols of Halloween, remember that it's a day of special astronomical meaning too - a cross quarter day marking the earth's yearly progress around the sun. Happy Cross-Quarter Day!