In Denmark, we are a ways off the equator, and have four seasons of roughly equal length. It would seem logical then, to use the seasons as a means of keeping time. Thus the following system arose:

Winter: Dec. 1 - Feb. 28/29
Spring: Mar. 1 - May 31
Summer: Jun. 1 - Aug. 31
Fall: Sep. 1 - Nov. 30

Not very complicated, and kind of makes sense, so I can live with that.

The scientific definition would probably be under equinox, for what it's worth (or solstice for winter/summer).

I was surprised by the English Wikipedia (http://en.wikipedia.org/wiki/Autumn) and by Slashdot (http://slashdot.org/...re-Fall-starts-), that none of them mention September 21st as the start date of autumn.

It says:

If you mean to say that people use the 21st even if the equinox falls on another day - no, I've never heard that definition. And I'm in Europe. I'm not sure who you mean by "they say"?

I suspect it's only used as a rough estimate, when people don't know when exactly the equinox is. I wasn't sure myself, and probably would have guessed the 21st as being the equinox date. Part of the confusion probably comes from the fact that the Spring equinox does fall slightly earlier, sometimes on the 21st ( http://en.wikipedia.org/wiki/Equinox ), and also that for Winter and Summer, the solstice dates are usually the 21. Wikipedia says:

Currently, the most common equinox and solstice dates are March 20, June 21, September 22 and December 21

So I can see why people might think 21 as an easy approximation for all four seasons. But I've not known anyone using the 21st as an absolute definition. Most people I think use the months definition anyway.

[quote name='Lode' timestamp='1315143425' post='4857474']
In Europe, they say (although astronomically speaking it usually differs by a few days) that autumn starts on September 21st, winter on December 21st, Spring on March 21st, and Summer on July 21st. Compare the English Wikipedia article with the Dutch one for example (http://nl.wikipedia.org/wiki/Herfst), and note the table full of dates which are all a few days after September 21st.

That's just wrong. Isn't December 21st the winter solstice? i.e. the exact middle of winter, not the start.[/quote]

The problem with positioning the seasons so that the solstices/equinoxes are at the midpoint of the season, is due to lag in the temperature. I mean, is November always as cold as January, or May as warm as July, where you are?

(Using the solstice/equinoxes as the starts may seem a bit late on the other hand, but that's why people usually use the months definition, so Winter starts 1st December, etc.)

In Denmark, we are a ways off the equator, and have four seasons of roughly equal length. It would seem logical then, to use the seasons as a means of keeping time. Thus the following system arose:

Winter: Dec. 1 - Feb. 28/29
Spring: Mar. 1 - May 31
Summer: Jun. 1 - Aug. 31
Fall: Sep. 1 - Nov. 30

Those are the dates I've always thought of as the seasons.

Hi guys! Don't forget about the other half of the world! In my Country (Argentina):

Summer: Dec. 21 - March 21
Autumn: March 21 - June 21
Winter: June 21 - Sept. 21
Spring: Sept. 21 - Dec. 21

Basically it's always a 21st, and usually flip the season with the other half (if it's winter here, it's summer there. If it's autumn here, then it's spring there).
By the way, particularly in my country the 21st September is often celebrated as the "Spring day". It isn't a holiday, though it coincides with the "Student day" where university students (the wikipedia article incorrectly states all "educational levels", though depends on the year and political agenda) don't have class.

um matias but did you ever think those dates were wrong?I think that was the whole point of the post the ~21 dates are way too laste WRT to reality
eg u live in argentine now go and check where spring/summer/winter etc occurs in the calender

Hi guys! Don't forget about the other half of the world! In my Country (Argentina):

Summer: Dec. 21 - March 21
Autumn: March 21 - June 21
Winter: June 21 - Sept. 21
Spring: Sept. 21 - Dec. 21

Basically it's always a 21st, and usually flip the season with the other half (if it's winter here, it's summer there. If it's autumn here, then it's spring there).
By the way, particularly in my country the 21st September is often celebrated as the "Spring day". It isn't a holiday, though it coincides with the "Student day" where university students (the wikipedia article incorrectly states all "educational levels", though depends on the year and political agenda) don't have class.

In Belgium the university students don't have class on Septembert 21st either because the academic year only starts the last week of September!

According to the Norwegian wikipedia page about "Høst" ("Autumn", "fall"), there are several definitions how to define the beginning of the autumn:

(I'll just cite a google translate of the wiki-page.)

[color="#333333"][font="arial, sans-serif"]"Fall[/font][color="#333333"][font="arial, sans-serif"] [/font][color="#333333"][font="arial, sans-serif"]is one of[/font][color="#333333"][font="arial, sans-serif"] [/font][color="#333333"][font="arial, sans-serif"]the four[/font][color="#333333"][font="arial, sans-serif"] [/font][color="#333333"][font="arial, sans-serif"]seasons[/font][color="#333333"][font="arial, sans-serif"] [/font][color="#333333"][font="arial, sans-serif"]in temperate[/font][color="#333333"][font="arial, sans-serif"] [/font][color="#333333"][font="arial, sans-serif"]and arctic[/font][color="#333333"][font="arial, sans-serif"] [/font][color="#333333"][font="arial, sans-serif"]zones[/font][color="#333333"][font="arial, sans-serif"] [/font][color="#333333"][font="arial, sans-serif"]of the globe [/font][color="#333333"][font="arial, sans-serif"] [/font][color="#333333"][font="arial, sans-serif"]and[/font][color="#333333"][font="arial, sans-serif"] [/font][color="#333333"][font="arial, sans-serif"]made[/font][color="#333333"][font="arial, sans-serif"] [/font][color="#333333"][font="arial, sans-serif"]??in the traditional[/font][color="#333333"][font="arial, sans-serif"] [/font][color="#333333"][font="arial, sans-serif"]context[/font][color="#333333"][font="arial, sans-serif"] [/font][color="#333333"][font="arial, sans-serif"]of the months[/font][color="#333333"][font="arial, sans-serif"] [/font][color="#333333"][font="arial, sans-serif"]September, October[/font][color="#333333"][font="arial, sans-serif"] [/font][color="#333333"][font="arial, sans-serif"]and November[/font][color="#333333"][font="arial, sans-serif"] [/font][color="#333333"][font="arial, sans-serif"]in the northern[/font][color="#333333"][font="arial, sans-serif"] [/font][color="#333333"][font="arial, sans-serif"]hemisphere[/font][color="#333333"][font="arial, sans-serif"] [/font][color="#333333"][font="arial, sans-serif"]and March[/font][color="#333333"][font="arial, sans-serif"], April[/font][color="#333333"][font="arial, sans-serif"] [/font][color="#333333"][font="arial, sans-serif"]and May[/font][color="#333333"][font="arial, sans-serif"] [/font][color="#333333"][font="arial, sans-serif"]in the Southern [/font][color="#333333"][font="arial, sans-serif"] [/font][color="#333333"][font="arial, sans-serif"]Hemisphere[/font][color="#333333"][font="arial, sans-serif"].[/font]
[color="#333333"][font="arial, sans-serif"] [/font]
[color="#333333"][font="arial, sans-serif"]The[/font][color="#333333"][font="arial, sans-serif"] [/font][color="#333333"][font="arial, sans-serif"]astronomical[/font][color="#333333"][font="arial, sans-serif"] [/font][color="#333333"][font="arial, sans-serif"]autumn[/font][color="#333333"][font="arial, sans-serif"] [/font][color="#333333"][font="arial, sans-serif"]is the period[/font][color="#333333"][font="arial, sans-serif"] [/font][color="#333333"][font="arial, sans-serif"]from the[/font][color="#333333"][font="arial, sans-serif"] [/font][color="#333333"][font="arial, sans-serif"]autumn[/font][color="#333333"][font="arial, sans-serif"] [/font][color="#333333"][font="arial, sans-serif"]equinox[/font][color="#333333"][font="arial, sans-serif"] [/font][color="#333333"][font="arial, sans-serif"]to the[/font][color="#333333"][font="arial, sans-serif"] [/font][color="#333333"][font="arial, sans-serif"]winter solstice[/font][color="#333333"][font="arial, sans-serif"],[/font][color="#333333"][font="arial, sans-serif"] [/font][color="#333333"][font="arial, sans-serif"]and[/font][color="#333333"][font="arial, sans-serif"] [/font][color="#333333"][font="arial, sans-serif"]the[/font][color="#333333"][font="arial, sans-serif"] [/font][color="#333333"][font="arial, sans-serif"]concurrent[/font][color="#333333"][font="arial, sans-serif"] [/font][color="#333333"][font="arial, sans-serif"]fall[/font][color="#333333"][font="arial, sans-serif"] [/font][color="#333333"][font="arial, sans-serif"]astrological[/font][color="#333333"][font="arial, sans-serif"] [/font][color="#333333"][font="arial, sans-serif"]signs are[/font][color="#333333"][font="arial, sans-serif"] [/font][color="#333333"][font="arial, sans-serif"]weight[/font][color="#333333"][font="arial, sans-serif"],[/font][color="#333333"][font="arial, sans-serif"] [/font][color="#333333"][font="arial, sans-serif"]Scorpio[/font][color="#333333"][font="arial, sans-serif"] [/font][color="#333333"][font="arial, sans-serif"]and [/font][color="#333333"][font="arial, sans-serif"] [/font][color="#333333"][font="arial, sans-serif"]Sagittarius[/font][color="#333333"][font="arial, sans-serif"].[/font]
[color="#333333"][font="arial, sans-serif"] [/font]
[color="#333333"][font="arial, sans-serif"]In[/font][color="#333333"][font="arial, sans-serif"] [/font][color="#333333"][font="arial, sans-serif"]meteorology[/font][color="#333333"][font="arial, sans-serif"] [/font][color="#333333"][font="arial, sans-serif"]defined[/font][color="#333333"][font="arial, sans-serif"] [/font][color="#333333"][font="arial, sans-serif"]fall[/font][color="#333333"][font="arial, sans-serif"] [/font][color="#333333"][font="arial, sans-serif"]to as[/font][color="#333333"][font="arial, sans-serif"] [/font][color="#333333"][font="arial, sans-serif"]the period when[/font][color="#333333"][font="arial, sans-serif"] [/font][color="#333333"][font="arial, sans-serif"]the normal[/font][color="#333333"][font="arial, sans-serif"] [/font][color="#333333"][font="arial, sans-serif"]daily mean temperature [/font][color="#333333"][font="arial, sans-serif"] [/font][color="#333333"][font="arial, sans-serif"]for that[/font][color="#333333"][font="arial, sans-serif"] [/font][color="#333333"][font="arial, sans-serif"]site[/font][color="#333333"][font="arial, sans-serif"] [/font][color="#333333"][font="arial, sans-serif"]is between[/font][color="#333333"][font="arial, sans-serif"] [/font][color="#333333"][font="arial, sans-serif"]0 and[/font][color="#333333"][font="arial, sans-serif"] [/font][color="#333333"][font="arial, sans-serif"]10 °[/font][color="#333333"][font="arial, sans-serif"] [/font][color="#333333"][font="arial, sans-serif"]C[/font][color="#333333"][font="arial, sans-serif"] [/font][color="#333333"][font="arial, sans-serif"]and falling[/font][color="#333333"][font="arial, sans-serif"].[/font][color="#333333"][font="arial, sans-serif"] [/font][color="#333333"][font="arial, sans-serif"]In the article[/font][color="#333333"][font="arial, sans-serif"] [/font][color="#333333"][font="arial, sans-serif"]about[/font][color="#333333"][font="arial, sans-serif"] [/font][color="#333333"][font="arial, sans-serif"]the season[/font][color="#333333"][font="arial, sans-serif"] [/font][color="#333333"][font="arial, sans-serif"]is [/font][color="#333333"][font="arial, sans-serif"] [/font][color="#333333"][font="arial, sans-serif"]given[/font][color="#333333"][font="arial, sans-serif"] [/font][color="#333333"][font="arial, sans-serif"]in the fall[/font][color="#333333"][font="arial, sans-serif"] [/font][color="#333333"][font="arial, sans-serif"]after this[/font][color="#333333"][font="arial, sans-serif"] [/font][color="#333333"][font="arial, sans-serif"]starts[/font][color="#333333"][font="arial, sans-serif"] [/font][color="#333333"][font="arial, sans-serif"]some[/font][color="#333333"][font="arial, sans-serif"] [/font][color="#333333"][font="arial, sans-serif"]places in[/font][color="#333333"][font="arial, sans-serif"] [/font][color="#333333"][font="arial, sans-serif"]Norway."[/font]
[color="#333333"][font="arial, sans-serif"] [/font]

um matias but did you ever think those dates were wrong?I think that was the whole point of the post the ~21 dates are way too laste WRT to reality
eg u live in argentine now go and check where spring/summer/winter etc occurs in the calender

They may be, they may not, but those are official in my Country. Anyway the point was that it's the opposite in the southern hemisphere