Which calendar, introduced in 46 BC, had a regular year of 365 days divided into 12 months, and a leap day added to February every four years?
It could be the Gregorian calendar
Which planet has a year of 687 days, a day of 24 hours 37 minutes, a diameter twice that of the moon and a mass one tenth of the earth?
How many approximate days are there in the Hijri (Islamic) Calender, the lunar calendar based on year 622 AD when Prophet Muhammed emigrated to Madina ?
What was the name of the regular feature of the European motorsport calendar from 1927 to 1957 that was held 24 times in Italy?