http://www.newsweek.com/google-doodle-bach-birthday-when-march-21-22-1366826

Google released its first ever artificial intelligence-powered doodle this week to honor the German composer Johann Sebastian Bach's birthday. The doodle was released Thursday and was set to run through Friday for a full 48-hour period. 

Bach was born on March 21 on the Julian calendar that is no longer used, today on the Gregorian calendar his birthday was be March 31. Google however, was honoring the composer on the original date of his birthday.