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December 31, 2009 9:53 AM   Subscribe

Why does our year start when it does?

After 29 trips around the sun, I've realized I don't know why our year starts when it does.

Wikipedia's page on the Julian calendar claims that January 1 was the start of the consulary year, but then the article goes on about how the Julian reform was preceded by a 445 day year to align January 1 with the "start of the tropical year". The tropical year, however, doesn't have an obvious start for me.

What's the story, AskMe?
posted by themel to Science & Nature (9 answers total)
The Infoplease article is pretty good about the history of this in Europe (the Julian Calendar article would also help answer your question).

Of course there are a kajillion other calendrical traditions in other parts of the world, but that's another question.
posted by Sidhedevil at 10:02 AM on December 31, 2009

I have always assumed that the new year is celebrated at this point, because this is when our ancestors could tell that the days were really beginning to get longer again.

I would be interested to see a better reason.
posted by Midnight Skulker at 10:19 AM on December 31, 2009

The Wall St. Journal actually had an article about this topic earlier in the week.
posted by dfriedman at 10:20 AM on December 31, 2009

The tropical year, however, doesn't have an obvious start for me.

Perihelion is (near) 1 January, with variation from orbital eccentricities.
posted by ROU_Xenophobe at 10:21 AM on December 31, 2009

In England, the new year started in March until 400 or so years ago. So you might have:
December 1545
January 1545
February 1545
March 1-15 1545
March 16, 1546
posted by atrazine at 10:55 AM on December 31, 2009

"The Calendar" by David Ewing Duncan is a great book with some clear answers to all your calendar-related questions. Including this one:

The decision to standardise the modern New Year's Day on January 1st was taken by a commision set up by pope Gregory XIII in 1580 - this was basically a decision to standardise on the day set by Julius Ceasar. The decision was implemented in 1582 as the Gregorian calendar.

Caesar's calendar had, in turn, been derived from that of the ancient Egyptians. They had noticed that the dog star, Syrius, ascends in the dawn sky directly in line with the rising sun periodically. This period happened to co-incide with the flooding of the Nile and the date thus becamse the start of the Egyptian month of Thoth and a marker for the new year. The period was originally timed as 365 days - but with more advanced astronomical observations the astronomers saw that they needed to add an extra quarter day. The priests who controlled the calendar would not let them. The Julian calendar, however added the extra quarter day.
posted by rongorongo at 11:04 AM on December 31, 2009

@ROU_Xenophobe: I think people didn't know when perihelion was until long after the start of the year was set as 1/1. And since Earth's orbit is nearly circular, perihelion isn't really that significant.
posted by madcaptenor at 11:51 AM on December 31, 2009

It's not the orbit path that makes perihelion significant, it is the tilt of the earth. Days start getting longer = spring will be along shortly and thus the new year has begun.
posted by gjc at 3:36 PM on December 31, 2009

Response by poster: Thanks, everyone. I don't necessarily feel more enlightened, but at least I can now make dinner party conversation about my ignorance. Happy 2010 everyone!
posted by themel at 5:23 PM on December 31, 2009

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