Saw this on 'Astronomy Picture of the Day' (one of my daily stops on the Internet). Today, February 29th, is a leap day - a relatively rare occurrence. In 46 BC, Julius Caesar, featured here in a self-decreed minted coin, created a calendar system that added one leap day every four years. Acting on advice by Alexandrian astronomer Sosigenes, Caesar did this to make up for the fact that the Earth's year is slightly more than 365 days. In modern terms, the time it takes for the Earth to circle the Sun is slightly more than the time it takes for the Earth to rotate 365 times (with respect to the Sun -- actually we now know this takes about 365.24219 rotations). So, if calendar years contained 365 days they would drift from the actual year by about 1 day every 4 years. Eventually July (named posthumously for Julius Caesar himself) would occur during the northern hemisphere winter! By adopting a leap year with an extra day every four years, the calendar year would drift much less. This Julian Calendar system was used until the year 1582 when Pope Gregory XIII provided further fine-tuning when he added that leap days should not occur in years ending in "00", unless divisible by 400. This Gregorian Calendar system is the one in common use today.
Eesh, you to fast Doug, was gonna' post a thread on this too! It's got some great info, thanks for sharin'!!
A timely post! I was trying to think of an appropriate coin, then it came to me: Sol and his high priest, duh. Denarius of Elagabalus...
By that time, they didn't even know that the Earth turns around the sun. I don't understand how can they scientifically conceive a leap year or a leap day in an adequate and logical method ?
They knew the sun and moon moved in cycles, just didn't understand why. By JC's time they had figured out a year is ~365 days. Took longer to narrow that to ~365.25, and now ~365.2422 days. Our ancestors were able to observe and measure precession cycle of the earth. That's considerably more difficult than its revolution around the sun.
Aristarchus of Samos proposed the sun was the center in the 3rd Century BC. Christian dogma made this view unacceptable for reasons having nothing to do with science. What Caesar though on the matter, I do not know but don't be too quick to insist his science advisers were ignorant of how this worked. Ptolemy in the 2nd century AD was a proponent of ethnocentrism but there are suggestions in works between those dates that suggest at least some serious astronomers understood.
There's no doubt some cultures understood that earth was a globe at very early dates. The great pyramid of Giza is a mathematical model of the planet. Whoever built it couldn't had scaled it so precisely without understanding of how earth, and the solar system works. If one takes the circumference of earth at the latitude of the great pyramids (29:58:51N), and divide that by the arc distance between the equator and the pyramids, you get a ratio around 10.1456 Take the number of days in a year (365.24218...) divide by 360, you would get the same ratio, 10.1456. Does that mean builders of the great pyramids had pinpointed earth year to 5th digit after decimal?
I need to recall that in 1492 when Christopher Columbus reached America, the aim or even main purpose of his travel was to sail west and straight starting from Europe in order to reach India. By doing so, he would prove indeed that the Earth is round. He was encouraged on his ship Santa Maria by many scientists, geographers, as well as the king and queen of Spain. That would suggest it wasn't admitted yet that the Earth was round.
