Everyday I go on wikipedia for about 20-30 minutes and learn about something completely unrelated to any classes or anything like that. I learned about the Julian calendar this morning.
If anyone is interested in a history lesson (somewhat inaccurate probably, as I'm just writing what I remember), read on.
So...
Julius Caesar instituted a calendar with 365 days, just like the Gregorian one we have today. This calendar even had leap years every four years, as does ours. In 325 CE, the council of Nicea arranged Easter to fall on a certain date relative to the vernal equinox. No problem, except that the Julian calendar (averaging 365.25 years) is eleven minutes off compared to the solar year. Every 136 years or so, this adds up to being a whole day off. By the early 16th century (maybe 1536, I forget), this problem resulted in a discrepancy of ten days between the solar year and the calendar year (the equinox and solstice dates were off). A change was made to the Gregorian calendar, and an instantaneous shift of 10 calendar days occurred. To those taking notes, this affects geneology charts including age if a person was born on Julian (Old) time and died on Gregorian (New) time.
That's the tidbit.
Now, the Gregorian calendar and the Julian calendar both average 365.25 days (w/ leap years); how did the new calendar solve the problem of the extra 11 minutes? Here's what I thought was really cool:
Since ~136 years of calendar time results in 1 day of shift, then we would be off by 3 days approximately every 400 years. In our calendar, leap years do not occur on century years that are not divisible by 400. We had a leap year in 2000, but there wasn't one in 1900, 1800, 1700. There was one in 1600, and the next on on a century year will be in 2400. The way this works is that every 4 centuries (400 years) we ignore 3 of the leap days and the calendar lines back up with solar time! Pretty neat if you ask me.
This whole thing raises a more interesting issue though...
If we were off by eleven minutes, then isn't our concept of a "second" somehow inherently wrong? I haven't looked into it, but I imagine it is defined by the period of a pendulum of a certain length. In more recent times, it has been defined as the half life of some atom (too lazy to do the research); this is, however, irrelevant, as it was instituted because it was the same duration of time as a "second" was already known to be. Why can't each second be marginally longer, thus making up the time discrepancy over the course of a year? I don't think that anyone would notice if each second were merely...
31558260 (w/ 11 more min to = solar yr) / 31557600 (sec/yr currently)
= 1.00002091
= 0.00002091% longer...
I do think the Gregorian solution is pretty smart though.
edit: I was vague in indicating which way the solar/calendar years are off. See below.
A calendar year is 365 days and 6 hours
A solar year is 365 days, 5 hours, 49 minutes, and 12 seconds.
If anyone is interested in a history lesson (somewhat inaccurate probably, as I'm just writing what I remember), read on.
So...
Julius Caesar instituted a calendar with 365 days, just like the Gregorian one we have today. This calendar even had leap years every four years, as does ours. In 325 CE, the council of Nicea arranged Easter to fall on a certain date relative to the vernal equinox. No problem, except that the Julian calendar (averaging 365.25 years) is eleven minutes off compared to the solar year. Every 136 years or so, this adds up to being a whole day off. By the early 16th century (maybe 1536, I forget), this problem resulted in a discrepancy of ten days between the solar year and the calendar year (the equinox and solstice dates were off). A change was made to the Gregorian calendar, and an instantaneous shift of 10 calendar days occurred. To those taking notes, this affects geneology charts including age if a person was born on Julian (Old) time and died on Gregorian (New) time.
That's the tidbit.
Now, the Gregorian calendar and the Julian calendar both average 365.25 days (w/ leap years); how did the new calendar solve the problem of the extra 11 minutes? Here's what I thought was really cool:
Since ~136 years of calendar time results in 1 day of shift, then we would be off by 3 days approximately every 400 years. In our calendar, leap years do not occur on century years that are not divisible by 400. We had a leap year in 2000, but there wasn't one in 1900, 1800, 1700. There was one in 1600, and the next on on a century year will be in 2400. The way this works is that every 4 centuries (400 years) we ignore 3 of the leap days and the calendar lines back up with solar time! Pretty neat if you ask me.
This whole thing raises a more interesting issue though...
If we were off by eleven minutes, then isn't our concept of a "second" somehow inherently wrong? I haven't looked into it, but I imagine it is defined by the period of a pendulum of a certain length. In more recent times, it has been defined as the half life of some atom (too lazy to do the research); this is, however, irrelevant, as it was instituted because it was the same duration of time as a "second" was already known to be. Why can't each second be marginally longer, thus making up the time discrepancy over the course of a year? I don't think that anyone would notice if each second were merely...
31558260 (w/ 11 more min to = solar yr) / 31557600 (sec/yr currently)
= 1.00002091
= 0.00002091% longer...
I do think the Gregorian solution is pretty smart though.
edit: I was vague in indicating which way the solar/calendar years are off. See below.
A calendar year is 365 days and 6 hours
A solar year is 365 days, 5 hours, 49 minutes, and 12 seconds.
Last edited:
