More proof that time is not linear:
The time it takes the Earth to revolve around the sun depends on what you refer the motion to. If you measure the Earth's revolution with respect to the stars, it's called a sidereal year, it takes our planet 365.2564 days to go around once. If you measure with respect to the vernal equinox - the point on the sky where the sun crosses the celestial equator moving from south to north, which occurs on the first day of spring - it takes 365.242199 days. This so-called tropical year ends up about 20 minutes shorter than a sidereal year, thanks to the precession of the equinoxes.
Calendar-makers chose to align the calendar with the seasons, so it is based on the tropical year. Unfortunately, that 0.242199 of a day makes it impossible to keep the calendar perfect. The first successful attempt to bring some order came with Julius Caesar, who in 46BC instituted a calendar reform that decreed a leap year every fourth year. That gives a year averaging 365.25 days, just 11 minutes and 14 seconds longer than a tropical year. Not a big descrepancy, but those minutes added up.
By 1582, 13 days had accumulated and the vernal equinox came on March 11. To prevent further slippage, Pope Gregory XIII dropped ten days from the calendar by proclaiming the day after October 4, 1582 to be October 15. He also modified the rule for leap years so that the years divisible evenly by 100 would not have an extra day unless they were also divisible by 400. The Gregorian calendar matches the tropical year to within a day about every 3,300 years.
But there is one noticeable effect that arises from the different lengths of the sidereal and the tropical years. Instead of the seasons falling earlier as the centuries pass, it's the stars that get out of whack. Over time, the stars we associate with a given season will change. By 15,000 AD Orion will no longer hunt the winter sky, but will forage in the summer air for prey.
The time it takes the Earth to revolve around the sun depends on what you refer the motion to. If you measure the Earth's revolution with respect to the stars, it's called a sidereal year, it takes our planet 365.2564 days to go around once. If you measure with respect to the vernal equinox - the point on the sky where the sun crosses the celestial equator moving from south to north, which occurs on the first day of spring - it takes 365.242199 days. This so-called tropical year ends up about 20 minutes shorter than a sidereal year, thanks to the precession of the equinoxes.
Calendar-makers chose to align the calendar with the seasons, so it is based on the tropical year. Unfortunately, that 0.242199 of a day makes it impossible to keep the calendar perfect. The first successful attempt to bring some order came with Julius Caesar, who in 46BC instituted a calendar reform that decreed a leap year every fourth year. That gives a year averaging 365.25 days, just 11 minutes and 14 seconds longer than a tropical year. Not a big descrepancy, but those minutes added up.
By 1582, 13 days had accumulated and the vernal equinox came on March 11. To prevent further slippage, Pope Gregory XIII dropped ten days from the calendar by proclaiming the day after October 4, 1582 to be October 15. He also modified the rule for leap years so that the years divisible evenly by 100 would not have an extra day unless they were also divisible by 400. The Gregorian calendar matches the tropical year to within a day about every 3,300 years.
But there is one noticeable effect that arises from the different lengths of the sidereal and the tropical years. Instead of the seasons falling earlier as the centuries pass, it's the stars that get out of whack. Over time, the stars we associate with a given season will change. By 15,000 AD Orion will no longer hunt the winter sky, but will forage in the summer air for prey.
VIEW 3 of 3 COMMENTS
that was sexy beyond belief. talk documentary to me, baby.
hugs,
~psychicgoldfish
snap!