# Why isn't the first day of fall... **URL:** \ **Category:** Factual Questions\ **Created:** [September 22, 2011, 3:04am UTC](https://boards.straightdope.com/t/why-isnt-the-first-day-of-fall/597143 "2011-09-22T03:04:50Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![67java89](https://avatars.discourse-cdn.com/v4/letter/6/aeb1de/32.png) [@67java89](https://boards.straightdope.com/u/67java89)\ **Post date:** [September 22, 2011, 3:04am UTC](https://boards.straightdope.com/t/why-isnt-the-first-day-of-fall/597143/1 "2011-09-22T03:04:50Z")
on the same date every year? Sometimes it’s on September 22, but other years it’s on the 21st or 23rd. What gives? ---
**Author:** ![Siam\_Sam](https://avatars.discourse-cdn.com/v4/letter/s/d78d45/32.png) [@Siam\_Sam](https://boards.straightdope.com/u/Siam_Sam)\ **Post date:** [September 22, 2011, 3:10am UTC](https://boards.straightdope.com/t/why-isnt-the-first-day-of-fall/597143/2 "2011-09-22T03:10:31Z")
Because it depends on the day that the [autumnal equinox](http://en.wikipedia.org/wiki/Equinox) actually occurs. It’s not like Congress legislates these things. ---
**Author:** ![Cugel](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cugel/32/1199_2.png) [@Cugel](https://boards.straightdope.com/u/Cugel)\ **Post date:** [September 22, 2011, 3:23am UTC](https://boards.straightdope.com/t/why-isnt-the-first-day-of-fall/597143/3 "2011-09-22T03:23:34Z")
It is. 1st March every year. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [September 22, 2011, 5:49am UTC](https://boards.straightdope.com/t/why-isnt-the-first-day-of-fall/597143/4 "2011-09-22T05:49:53Z")
Unless you consider Labor Day to be the first day of fall, in which case Congress _does_ legislate these things. But to the question the OP was probably asking, it’s not the equinox shifting relative to our calendar, but our calendar shifting relative to the equinox. Leap years are the biggest reason for this. ---
**Author:** ![Floater](https://avatars.discourse-cdn.com/v4/letter/f/dc4da7/32.png) [@Floater](https://boards.straightdope.com/u/Floater)\ **Post date:** [September 22, 2011, 11:44am UTC](https://boards.straightdope.com/t/why-isnt-the-first-day-of-fall/597143/5 "2011-09-22T11:44:39Z")
Why would the first day of autumn be on a certain date? Seasons are determined by temperature, not calendars. ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [September 22, 2011, 11:52am UTC](https://boards.straightdope.com/t/why-isnt-the-first-day-of-fall/597143/6 "2011-09-22T11:52:59Z")
> [@67java89](#): > > on the same date every year? Sometimes it’s on September 22, but other years it’s on the 21st or 23rd. What gives? We have a leapyear roughly every four years, when a full day is added to the end of February to account for the accumulation of about a day of error, over the previous four years, between our calendar and the phase of earth’s orbit around the sun. Correspondingly, the important points of the earth’s orbit - spring/fall equinox, and winter/summer solstice - also shift around on the calendar. Note that those [solstice](http://en.wikipedia.org/wiki/Solstice) and[equinox](http://en.wikipedia.org/wiki/Equinox) events are points - instantaneous moments in time - rather than full days. So even though there’s only a quarter of a day change in the timing of any of these events on the calendar, you may see it switch backward one day on the calendar if there’s a leap year, and then one day forward the next year if it’s being dithered back and forth across a midnight. ---
**Author:** ![Philster](https://avatars.discourse-cdn.com/v4/letter/p/13edae/32.png) [@Philster](https://boards.straightdope.com/u/Philster)\ **Post date:** [September 22, 2011, 12:09pm UTC](https://boards.straightdope.com/t/why-isnt-the-first-day-of-fall/597143/7 "2011-09-22T12:09:31Z")
> [@Floater](#): > > Why would the first day of autumn be on a certain date? Seasons are determined by temperature, not calendars. A season is 1/4 of the trip around the sun. Temperatures are irrelevant. ---
**Author:** ![CookingWithGas](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cookingwithgas/32/485_2.png) [@CookingWithGas](https://boards.straightdope.com/u/CookingWithGas)\ **Post date:** [September 22, 2011, 12:18pm UTC](https://boards.straightdope.com/t/why-isnt-the-first-day-of-fall/597143/8 "2011-09-22T12:18:57Z")
Astronomical fall begins on the equinox, which is defined as the moment when the center of the sun is in the same plane defined by the Earth’s equator. However, there is also meteorological fall, which is defined by dates. It starts September 1. If seasons were defined by temperature then we would have had a few days of fall last week, and we’ll have a couple of days of summer next week, and we might even get a couple of days of spring in January. ---
**Author:** ![Floater](https://avatars.discourse-cdn.com/v4/letter/f/dc4da7/32.png) [@Floater](https://boards.straightdope.com/u/Floater)\ **Post date:** [September 22, 2011, 1:37pm UTC](https://boards.straightdope.com/t/why-isnt-the-first-day-of-fall/597143/9 "2011-09-22T13:37:12Z")
[ul] [li]Meteorological summer starts when the mean temperature over 24 hours has been above 10 C during a period of 5 days.[/li][li]Meteorological autumn starts when the mean temperature over 24 hours has been below 10 C during a period of 5 days.[/li][li]Meteorological winter starts when the mean temperature over 24 hours has been below 0 C during a period of 5 days.[/li][li]Meteorological spring starts when the mean temperature over 24 hours has been above 0 C during a period of 5 days.[/li][/ul] Dates are irrelevant. ---
**Author:** ![Acsenray](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/acsenray/32/4519_2.png) [@Acsenray](https://boards.straightdope.com/u/Acsenray)\ **Post date:** [September 22, 2011, 2:06pm UTC](https://boards.straightdope.com/t/why-isnt-the-first-day-of-fall/597143/10 "2011-09-22T14:06:46Z")
> [@Philster](#): > > A season is 1/4 of the trip around the sun. Temperatures are irrelevant. A season is experiential. It has nothing to do with astronomy or meteorology. Fall has begun when it feels like it is fall. ---
**Author:** ![Telemark](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/telemark/32/372_2.png) [@Telemark](https://boards.straightdope.com/u/Telemark)\ **Post date:** [September 22, 2011, 2:14pm UTC](https://boards.straightdope.com/t/why-isnt-the-first-day-of-fall/597143/11 "2011-09-22T14:14:43Z")
> [@Floater](#): > > [ul] > [li]Meteorological spring starts when the mean temperature over 24 hours has been above 0 C during a period of 5 days.[/li][/ul] > Dates are irrelevant. There are many definitions of the seasons. Meteorological seasons are location specific, not used by many people, and not the subject of the OP. ---
**Author:** ![Lemur866](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lemur866/32/434_2.png) [@Lemur866](https://boards.straightdope.com/u/Lemur866)\ **Post date:** [September 22, 2011, 2:18pm UTC](https://boards.straightdope.com/t/why-isnt-the-first-day-of-fall/597143/12 "2011-09-22T14:18:49Z")
> [@Philster](#): > > A season is 1/4 of the trip around the sun. Temperatures are irrelevant. So do they have Spring, Summer, Fall, and Winter in Cameroon? ---
**Author:** ![Enderw24](https://avatars.discourse-cdn.com/v4/letter/e/ba9def/32.png) [@Enderw24](https://boards.straightdope.com/u/Enderw24)\ **Post date:** [September 22, 2011, 2:31pm UTC](https://boards.straightdope.com/t/why-isnt-the-first-day-of-fall/597143/13 "2011-09-22T14:31:43Z")
> [@Lemur866](#): > > So do they have Spring, Summer, Fall, and Winter in Cameroon? We have much to learn from them. ---
**Author:** ![CookingWithGas](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cookingwithgas/32/485_2.png) [@CookingWithGas](https://boards.straightdope.com/u/CookingWithGas)\ **Post date:** [September 22, 2011, 2:37pm UTC](https://boards.straightdope.com/t/why-isnt-the-first-day-of-fall/597143/14 "2011-09-22T14:37:34Z")
> [@Floater](#): > > [ul] > [li]Meteorological summer starts when the mean temperature over 24 hours has been above 10 C during a period of 5 days.[/li][li]Meteorological autumn starts when the mean temperature over 24 hours has been below 10 C during a period of 5 days.[/li][li]Meteorological winter starts when the mean temperature over 24 hours has been below 0 C during a period of 5 days.[/li][li]Meteorological spring starts when the mean temperature over 24 hours has been above 0 C during a period of 5 days.[/li][/ul] > Dates are irrelevant. According to a [paper available from the American Meteorological Society](http://docs.google.com/viewer?a=v&q=cache:WCs1EhilBVsJ:journals.ametsoc.org/doi/pdf/10.1175/1520-0477%281983%29064%253C1276%253AWATS%253E2.0.CO%253B2+definition+meteorilogical+summer+site:ametsoc.org&hl=en&gl=us&pid=bl&srcid=ADGEESj-Dk40-VuglXojkrSQADLqHLDBkPWQ0qT59KmCy2ZrBpZINHWKIwYVfurx7W2ZejLTAizonPHulta3VqbrWJNbi3xYcbOcVPQjrVcTGjZD16bSL-NyS5cHrmFY-FOOpA4l0S6m&sig=AHIEtbRsa7dE5SLddgEMr6JTAFw_Od1UfA), written by Kevin Trenberth of the Department of Atmospheric Sciences at University of Illinois at Urbana-Champaign, meteorological seasons are based on dates. > [@](#): > > …in meteorology, the most widely used breakdown into seasons is simply the subdivision into four three-month periods. Winter is December, January, and February, the three coldest months in the Northern Hemisphere; spring is March, April, and May; summer is the three warmest months, June, July, and August; and autumn is September, October, and November. ---
**Author:** ![Thudlow\_Boink](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/thudlow_boink/32/320_2.png) [@Thudlow\_Boink](https://boards.straightdope.com/u/Thudlow_Boink)\ **Post date:** [September 22, 2011, 2:37pm UTC](https://boards.straightdope.com/t/why-isnt-the-first-day-of-fall/597143/15 "2011-09-22T14:37:40Z")
> [@CookingWithGas](#): > > However, there is also meteorological fall, which is defined by dates. It starts September 1. [Cecil (and/or his climate-researcher source) appears to agree with you](http://www.straightdope.com/columns/read/161/is-it-true-summer-in-ireland-starts-may-1): [QUOTE=Cecil Adams] He notes that meteorologists define summer simply as June, July, and August. “For practical purposes, the meteorological definition is the best one, being very closely to the [weather] statistics,” he says. [/QUOTE] Cecil also weighs in against the idea that the first day of summer is “officially” on the solstice (and, by implication, that the first day of autumn must be the equinox). > [@](#): > > There is a widespread misconception in this country–which extends, I might note, to the makers of most calendars, dictionaries, and encyclopedias–that summer “officially” starts on the day of the summer solstice, June 21 or 22, which is the longest day of the year. Americans also believe (1) that there is some valid scientific reason for doing it that way, and (2) that everybody in the Northern Hemisphere does it that way, and always has. > > None of these things is true. So far as I have been able to discover, no scientific or governmental body has ever formally declared that summer starts on the solstice. ---
**Author:** ![tdn](https://avatars.discourse-cdn.com/v4/letter/t/94ad74/32.png) [@tdn](https://boards.straightdope.com/u/tdn)\ **Post date:** [September 22, 2011, 2:42pm UTC](https://boards.straightdope.com/t/why-isnt-the-first-day-of-fall/597143/16 "2011-09-22T14:42:09Z")
> [@Floater](#): > > Why would the first day of autumn be on a certain date? Seasons are determined by temperature, not calendars. So does fall start earlier in Toronto than it does in Atlanta? ---
**Author:** ![Ximenean](https://avatars.discourse-cdn.com/v4/letter/x/aca169/32.png) [@Ximenean](https://boards.straightdope.com/u/Ximenean)\ **Post date:** [September 22, 2011, 2:49pm UTC](https://boards.straightdope.com/t/why-isnt-the-first-day-of-fall/597143/17 "2011-09-22T14:49:52Z")
If we somewhat arbitrarily declare the seasons be of equal length, then a reasonable start date for autumn would be [equinox, minus half of three months, plus temperature lag due to oceans retaining heat]. The latter varies by location but is typically about one month. That gives a date of about September 8th. But September 1st seems close enough to me. ---
**Author:** ![Acsenray](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/acsenray/32/4519_2.png) [@Acsenray](https://boards.straightdope.com/u/Acsenray)\ **Post date:** [September 22, 2011, 2:55pm UTC](https://boards.straightdope.com/t/why-isnt-the-first-day-of-fall/597143/18 "2011-09-22T14:55:56Z")
> [@tdn](#): > > So does fall start earlier in Toronto than it does in Atlanta? Why not? In Bengal, there are six seasons – summer, monsoon, autumn, dry season, winter, spring ---
**Author:** ![Philster](https://avatars.discourse-cdn.com/v4/letter/p/13edae/32.png) [@Philster](https://boards.straightdope.com/u/Philster)\ **Post date:** [September 22, 2011, 2:58pm UTC](https://boards.straightdope.com/t/why-isnt-the-first-day-of-fall/597143/19 "2011-09-22T14:58:18Z")
> [@Lemur866](#): > > So do they have Spring, Summer, Fall, and Winter in Cameroon? Yes, but you just can’t tell them apart as easily as in some other areas, because the weather isn’t the leading indicator of the season in that given area. . ---
**Author:** ![Lemur866](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lemur866/32/434_2.png) [@Lemur866](https://boards.straightdope.com/u/Lemur866)\ **Post date:** [September 22, 2011, 2:59pm UTC](https://boards.straightdope.com/t/why-isnt-the-first-day-of-fall/597143/20 "2011-09-22T14:59:52Z")
> [@](#): > > …in meteorology, the most widely used breakdown into seasons is simply the subdivision into four three-month periods. Winter is December, January, and February, the three coldest months in the Northern Hemisphere; spring is March, April, and May; summer is the three warmest months, June, July, and August; and autumn is September, October, and November. Yes, yes, a thousand times yes. [Next page](https://boards.straightdope.com/t/why-isnt-the-first-day-of-fall/597143.md?page=2)