In the Northern hemisphere, the beginning of the meteorological autumn is on the 1st of September. In the Southern hemisphere, the beginning of the meteorological spring is on the 1st of September.
September begins on the same day of the week as December every year, because there are 91 days separating September and December, which is a multiple of seven (the number of days in the week). No other month ends on the same day of the week as September in any year. This month and May are the only two months to have this property. April and July of the previous year begin on the same day of the week as September of the current year as a common year, October of the previous year always begins on the same day of the week as September of the current year as a leap year, January of the previous year begins on the same day of the week as September of the current year as a leap year and a year immediately before that. In common years, September ends on the same day of the week as April and December of the previous year while in leap years, September ends on the same day of the week as July of the previous year. In years immediately before common years, September begins on the same day of the week as June of the following year and in years immediately before leap years, September begins on the same day of the week as March and November of the following year. In years immediately before common years, September ends on the same day of the week as March and June of the following year and in years immediately before leap years, September ends on the same day of the week as August and November of the following year.
September (from Latin septem, "seven") was originally the seventh of ten months on the oldest known Roman calendar, with March (Latin Martius) the first month of the year until perhaps as late as 153 BC. After the calendar reform that added January and February to the beginning of the year, September became the ninth month, but retained its name. It had 29 days until the Julian reform, which added a day.
September is mostly in the sixth month of the astrological calendar (and the first part of the seventh), which begins at the end of March/Mars/Aries.
The equinox named the autumnal equinox in the northern hemisphere and the vernal or spring equinox in the southern hemisphere occurs on dates varying from 21 September to 24 September (in UTC). In the pagan wheel of the year the spring equinox is the time of Ostara and the ] is celebrated on the first Sunday of September.
- 1 Month-long observances
- 2 Other observances
- 3 Non-Gregorian observances, 2015 dates
- 4 Movable Gregorian Observances, 2015 dates
- 4.1 Saturday before First Monday: September 5
- 4.2 First Sunday: September 6
- 4.3 First Sunday after September 4: September 6
- 4.4 First Monday: September 7
- 4.5 Thursday after the first Sunday: September 10
- 4.6 Second Saturday: September 12
- 4.7 Weekend after first Monday: September 12-13
- 4.8 Sunday after first Monday: September 13
- 4.9 Second Sunday: September 13
- 4.10 Weekday nearest September 17
- 4.11 Saturday closest Sept. 23: September 19
- 4.12 Third Weekend: September 19-20
- 4.13 Week of September 22: September 20-26
- 4.14 Sunday before September 23 to Saturday:September 20-26
- 4.15 Third Monday: September 21
- 4.16 Last Sunday: September 27
- 5 Fixed Gregorian observances
- 6 Miscellanea
- 7 September symbols
- 8 References
- 9 External links
- Amerindian Heritage Month (Guyana)
- Childhood Cancer Awareness Month
- Gynecologic Cancer Awareness Month
- Leukemia and Lymphoma Awareness Month
- Thyroid Cancer Awareness Month
United States observances
- National Ovarian Cancer Month
- National Preparedness Month
- National Prostate Cancer Awareness Month
- National Bourbon Heritage Month
- Better Breakfast Month
- California Wine Month
- Food Safety Education Month
- National Chicken Month
- National Childhood Obesity Awareness Month
- National Honey Month
- National Mushroom Month
- National Papaya Month
- National Potato Month
- National Rice Month
- National Sickle Cell Awareness Month
- National Whole Grains Month
- National Wild Rice Month
- National Hispanic Heritage Month (September 15-October 15)
- German American Heritage Month begins on September 15 in the United States.
- Take a Loved One to the Doctor Day (typically the last week in September)
- Constitution Week (United States) September 17-23
Non-Gregorian observances, 2015 dates
- Kumbh Mela (Hindu calendar) 29 Aug – 18 September
- Angarki Sankashti Chaturthi (Hindu calendar) September 1
- Krishna Janmashtami (Hindu calendar) September 5
- Gokarna Aunsi (Hindu calendar) September 13 
- Rosh HaShanah (Hebrew calendar) sunset, September 13 – nightfall, September 15 (Beginning of the Ten Days of Repentance)
- Gowri Habba (Hindu calendar) September 16
- Ganesh Chaturthi (Hindu calendar) September 17
- Fast of Gedalia (Hebrew calendar) September 18
- Nuakhai (Hindu calendar) September 18
- Thimbphu Drupchen September 19 (Thimphu, Bhutan)
- Radhastami (Hindu calendar) September 21
- Mahalakshmi Vrata (Hindu calendar) September 21-October 4
- Hajj (Islamic calendar) September 21
- Blessed Rainy Day (Bhutan, September 22) 
- Day of Arafah (Islamic calendar) September 22
- Yom Kippur (Hebrew calendar) Sunset, September 22 – nightfall, September 23 (End of the Ten Days of Repentance)
- Eid al-Adha (Islamic calendar) September 23
- Thimbphu Drubchoe September 23-25 (Thimphu, Bhutan)
- Anant Chaturdashi (Hindu calendar) September 26
- Chuseok (Korea) September 27
- Mid-Autumn Festival (China, Vietnam) September 27
- Sukkot (Hebrew calendar) September 27 - October 4
Movable Gregorian Observances, 2015 dates
Saturday before First Monday: September 5
First Sunday: September 6
First Sunday after September 4: September 6
- Wakes Week (Parts of England and Scotland) (September 6-12)
First Monday: September 7
Thursday after the first Sunday: September 10
Second Saturday: September 12
Weekend after first Monday: September 12-13
Saturday after first Monday: September 12
Sunday after first Monday: September 13
Second Sunday: September 13
- Auditor's Day (Church of Scientology)
- Father's Day (Latvia)
- National Grandparents' Day (Canada, Estonia, United States)
- Racial Justice Sunday (British Churches)
- Turkmen Bakhshi Day (Turkmenistan)
Weekday nearest September 17
- Constitution Day (United States) September 17
Saturday closest Sept. 23: September 19
Third Weekend: September 19-20
Sunday of the Third Weekend: September 20
- Cow Harbor Day (Northport, New York, United States)
- Day of the Walloon Region (Wallonia, Belgium)
- Federal Day of Thanksgiving, Repentance and Prayer (Switzerland
Week of September 22: September 20-26
Sunday before September 23 to Saturday:September 20-26
Third Monday: September 21
Last Sunday: September 27
Fixed Gregorian observances
- September 1
- Anniversary of the Start of the Armed Struggle (Eritrea)
- Constitution Day (Slovakia)
- Disaster Prevention Day (Japan)
- Flag Day (Honduras)
- Independence Day (Uzbekistan)
- Journalist Day (Taiwan)
- Knowledge Day (Russia)
- Random Acts of Kindness Day (New Zealand)
- Teachers' Day (Singapore)
- Wattle Day (Australia)
- September 2
- September 3
- China's victory over Japan commemoration related observances:
- Feast of San Marino and the Republic, celebrates the foundation of the Republic of San Marino in 301.
- Flag Day (Australia)
- Independence Day (Qatar)
- Levy Mwanawasa Day (Zambia)
- Memorial Day (Tunisia)
- Merchant Navy Remembrance Day (Canada)
- Merchant Navy (United Kingdom)
- September 4
- September 5
- September 6
- September 7
- September 8
- Feast of 'Izzat (Might), only if Bahá'í Naw-Rúz falls on March 21, which it does for 2015 (Bahá'í Faith)
- Independence Day (Republic of Macedonia)
- International Literacy Day
- Martyrs' Day (Afghanistan) (date may fall on September 9, follows a non-Gregorian calendar)
- National day (Andorra)
- Victory Day (Pakistan)
- Victory Day (Malta)
- September 9
- September 10
- September 11
- September 12
- September 13
- September 14
- September 15
- September 16
- September 17
- September 18
- September 19
- Second day of Fiestas Patrias (Chile)
- September 20
- September 21
- September 22
- September 23
- September 24
- September 25
- September 26
- September 27
- September 28
- September 29
- September 30
- In 1752, the British Empire adopted the Gregorian calendar. In the British Empire that year, September 2 was immediately followed by September 14.
- On Usenet, it is said that September 1993 (Eternal September) never ended.
- September in the Northern Hemisphere is the seasonal equivalent to March in the Southern Hemisphere and vice versa.
- The principal ecclesiastical feasts falling within the month are: the Nativity of the Blessed Virgin on the 8th, the Exaltation of the Holy Cross on the 14th, St. Matthew the apostle on the 21st, and St. Michael the archangel on the 29th.
- September was called "harvest month" in Charlemagne's calendar.
- September corresponds partly to the Fructidor and partly to the Vendémiaire of the first French republic.
- The Anglo-Saxons called the month Gerstmonath, barley month, that crop being then usually harvested.
- September is called Herbstmonat, harvest month, in Switzerland.
- The Chinese August Moon festival (more correctly called the Mid-Autumn Festival) usually occurs in September.
- As a celebration for the coming October, the traditional harvest month in historic Germany, the German Oktoberfest is celebrated near the end of September.
- Every third Tuesday in September, it is Prinsjesdag in the Netherlands, when the king will hold the Speech from the throne and the government will state its policy and budget plans in the Budget Memorandum for the next year. The plans are carried in a suitcase with the text "DERDE DINSDAG IN SEPTEMBER" (THIRD TUESDAY IN SEPTEMBER).
- Every fourth Monday in September, the Minister-President of Flanders reads the September Declaration to the Flemish Parliament about the state of affairs in society and what the Flemish Government plans to do next year.
- September's birthstone is the sapphire.
- The birth flowers for September are the forget-me-not, morning glory and aster.
- The zodiac signs for the month of September are Virgo (until September 21) and Libra (from September 22 onwards).
- Metoffice.gov.uk[dead link]
- H.H. Scullard, Festivals and Ceremonies of the Roman Republic (Cornell University Press, 1981), p. 84; Gary Forsythe, Time in Roman Religion: One Thousand Years of Religious History (Routledge, 2012), p. 14.
- "Fathers Day in Australia".
- "Food Days, Weeks, Months - September". UNL Food. University of Nebraska–Lincoln.
- Goldstein, Darra (2011). "National Turkey Day". Gastronomica 11 (4).
- "Ancestry.com". Ancestry.com. Retrieved 2013-08-22.
- Chisholm, Hugh, ed. (1911). "September". Encyclopædia Britannica (11th ed.). Cambridge University Press.
- SHG Resources. "SHGresources.com". SHGresources.com. Retrieved 2013-08-22.
- "Flowerstower.com". Archived from the original on February 24, 2013. Retrieved 2013-08-22.
- The dictionary definition of September at Wiktionary
- Media related to September at Wikimedia Commons
- Quotations related to September at Wikiquote