September (Sep.) is the ninth month of the year in the Gregorian calendar, coming between August and October. It has 30 days. Its name comes from the Latin word sept for "seven" (it was the seventh month of the year, before January and February were added to the beginning of the year.)

September always begins on the same day of the week as December, but never ends on the same day of the week as any other month.

The Month 

In the old Roman calendar, September was the seventh month, which is where it got its name ("Septem" means "seventh"). The ninth month at the time was November ("Novem" means "ninth"). With Julius Caesar's calendar reform, September became the ninth month, with 30 days. September comes after August and before October.

September begins on the same day of week as December every year, as each other's first days are 13 weeks (91 days) apart. No other month in any year ends on the same day of the week as September: this month and May are the only two months with this property.

In common years, September starts on the same day of the week as April and July of the previous year, and in leap years, October of the previous year. In common years, September finishes on the same day of the week as April and December of the previous year, and in leap years, July of the previous year. In leap years and years immediately after that, September starts on the same day of the week as January of the previous year.

In years immediately before common years, September starts on the same day of the week as June of the following year, and in years immediately before leap years, March and November of the following year. In years immediately before common years, September finishes on the same day of the week as March and June of the following year, and in years immediately before leap years, August and November of the following year.

September is one of two months to have an equinox (the other is March, its seasonal equivalent in both hemispheres), where both day and night are roughly of equal length, occurring either on the 22nd or 23rd, halfway between the June and December solstices. In the Northern Hemisphere, Autumn (Fall) begins in this month, while in the Southern Hemisphere, this is the beginning of Spring. For meteorologists, the people who study the weather, these seasons begin on September 1 in those hemispheres. In most Northern Hemisphere countries, school starts in this month, following the summer holidays.

In Ancient Greece, September was called Boedromion. The Anglo-Saxons called it Gerstmonath, meaning "Barley month", referring to the harvest. In other countries, it is referred to as Autumn Month, such as in Finland (Syyskuu) and German-speaking parts of Switzerland (Herbstmonat).

Ethiopian New Year occurs in September. Jewish New Year also often occurs in this month.

Events and Occurrences

Fixed Events 

 September 1  Independence Day (Uzbekistan)
 September 1  Armed Struggle for Independence (Eritrea)
 September 1  Constitution Day (Slovakia)
 September 2  Independence Day (Vietnam)
 September 3  National Day of San Marino
 September 3  Independence Day (Qatar)
 September 3  Flag Day (Australia)
 September 3  Levy Mwanawasa Day (Zambia)
 September 3  Merchant Navy Day (United Kingdom)
 September 5  Teacher's Day (India)
 September 6  Independence Day (Swaziland)
 September 6  Unification Day (Bulgaria)
 September 7  Independence Day (Brazil)
 September 7  National Threatened Species Day (Australia)
 September 7  Victory Day (Mozambique)
 September 8  National Day of Andorra
 September 8  Independence Day (Republic of Macedonia)
 September 8  Nativity of the Blessed Virgin (feast day in Christianity)
 September 9  Admission Day (California)
 September 9  National Day of North Korea
 September 9  Independence Day (Tajikistan)
 September 11  National Day of Catalonia
 September 11  Patriot Day (United States)
 September 11/12  Ethiopian New Year
 September 12  National Day of Cape Verde
 September 13  World Chocolate Day
 September 14  Exaltation of the Holy Cross (Roman Catholicism)
 September 15  Battle of Britain Day (United Kingdom)
 September 15  National Day of Costa Rica, El Salvador, Guatemala, Honduras and Nicaragua
 September 16  Independence Day (Mexico)
 September 16  Independence Day (Papua New Guinea)
 September 16  Malaysia Day
 September 17  Constitution Day (United States)
 September 18  Independence Day (Chile)
 September 19  Armed Forces Day (Chile)
 September 19  Independence Day (Saint Kitts and Nevis)
 September 19  International Talk Like a Pirate Day
 September 21  Independence Day (Malta)
 September 21  Independence Day (Belize)
 September 21  World Freedom Day/International Peace Day
 September 21  World Alzheimer's Day, raising awareness of Alzheimer's disease.
 September 22  Independence Day (Bulgaria)
 September 22  Independence Day (Mali)
 September 23  Equinox, Autumn (Fall) in the North, Spring in the South, can occur on September 22.
 September 23  National Day of Saudi Arabia
 September 24  National Day of Guinea-Bissau
 September 24  Heritage Day (South Africa)
 September 25  Revolution Day (Mozambique)
 September 26  European Day of Languages
 September 27  End of Independence War Day (Mexico)
 September 27  Holiday for the French-speaking community in Belgium
 September 28  World Heart Day
 September 28  World Rabies Day
 September 28  Ask a Stupid Question Day (United States)
 September 29  Inventors' Day (Argentina), honouring Laszlo Biro
 September 29  Christian feast day of Michaelmas, honouring St. Michael the Archangel
 September 29  Christian feast day of the three Archangels, honouring St. Michael, St. Gabriel and St. Raphael.
 September 29  International Coffee Day
 September 29  Victory of Boquerón Day (Paraguay)
 September 30  Independence Day (Botswana)

Moveable and Monthlong Events 

 The Summer Olympics sometimes occur in September, though mostly in July or August
 The Summer Paralympics are often held in September
 Yom Kippur, in the Jewish calendar, occurs in September or October.
 Labor Day (US and Canada), first Monday in September
 Prinsjesdag (Netherlands), third Tuesday in September
 Munich Oktoberfest runs in late September and the beginning of October.
 Start of school in most Northern Hemisphere countries
 German American Heritage Month and Hispanic Heritage Month (United States), run from September 15 to October 15.
 Marathons in September:
 Berlin, Germany
 Kathmandu, Nepal
 Mexico City, Mexico
 Oslo, Norway
 Sydney, Australia
 Tallinn, Estonia
 Vilnius, Lithuania

Selection of Historical Events 

 September 1  1715: The reign of Louis XIV of France ends with his death after 72 years on the throne.
 September 1  1914: Martha, the last Passenger Pigeon, dies, making her species extinct.
 September 1  1939: Nazi Germany invades Poland, starting World War II.
 September 1  1969: Muammar al-Gaddafi takes power in Libya, in a coup.
 September 1  1983: Korean Air Flight KAL-007 is shot down by a Soviet jet fighter, near Sakhalin Island, killing all 269 on board.
 September 1  1991: Uzbekistan becomes independent from the Soviet Union.
 September 2  1838: Liliuokalani, the last Hawaiian monarch, is born.
 September 2  1945: Japan signs the final surrender at the end of World War II.
 September 2  1945: Vietnam becomes independent, with Ho Chi Minh as leader.
 September 3  301: San Marino is founded.
 September 3  1939: The United Kingdom and France declare war on Germany, following its invasion of Poland.
 September 3  1950: Giuseppe Farina becomes the first Formula One racing champion.
 September 3  1967: Road traffic in Sweden is moved from the left to the right.
 September 3  1971: Qatar becomes independent.
 September 5  1972: Several members of the Israeli Olympic team are kidnapped at the 1972 Summer Olympics in Munich. They are killed the next day.
 September 6  1901: US President William McKinley is shot by Leon Czolgosz, dying over a week later.
 September 6  1968: Swaziland becomes independent.
 September 6  1997: The funeral of Diana, Princess of Wales takes place in London.
 September 7  1533: Queen Elizabeth I of England is born.
 September 7  1822: Brazil declares independence from Portugal
 September 7  1940: The World War II Battle of Britain begins.
 September 7  2011: All members of the Russian ice hockey team Lokomotiv Yaroslavl are killed in a plane crash.
 September 8  1943: US General Dwight D. Eisenhower announces the allied armistice with Italy during World War II.
 September 8  1991: The Republic of Macedonia declares independence from Yugoslavia.
 September 9  1850: California becomes the 31st State of the US.
 September 9  1991: Tajikistan becomes independent from the Soviet Union.
 September 10  1898: Elisabeth of Bavaria, Empress of Austria is stabbed to death by Italian anarchist Luigi Lucheni at Lake Geneva, Switzerland.
 September 10  1974: Guinea-Bissau officially becomes independent.
 September 10  2008: Scientists at CERN switch the Large Hadron Collider on for the first time.
 September 11  1973: Augusto Pinochet takes power in a military coup in Chile. President Salvador Allende dies during the coup.
 September 11  1997: Voters in Scotland approve the creation of a new Scottish Parliament.
 September 11  2001: The September 11 attacks occur, as Islamist terrorists crash airplanes into the World Trade Center in New York City and the Pentagon.
 September 12  1977: Anti-Apartheid activist Steve Biko dies in police custody.
 September 13  1759: Battle of the Plains of Abraham: British forces defeat French forces near Quebec City in the Seven Years' War.
 September 14  1752: Great Britain switches from the Julian calendar to the Gregorian calendar.
 September 14  1982: Grace Kelly dies after a car crash the previous day.
 September 15  1821: Costa Rica, El Salvador, Guatemala, Honduras and Nicaragua declare independence from Spain.
 September 16  1810: Mexico declares independence from Spain.
 September 16  1975: Papua New Guinea becomes independent from Australia.
 September 17  1787: The United States Constitution is signed in Philadelphia, Pennsylvania.
 September 17  2011: The Occupy Wall Street movement begins in New York City.
 September 18  1810: Chile declares independence.
 September 18  1970: Musician Jimi Hendrix dies in London, aged 27.
 September 19  1983: Saint Kitts and Nevis becomes independent.
 September 19  1985: Southern and Central Mexico are struck by a strong earthquake. Mexico City is among the places affected.
 September 21  1964: Malta gains independence from the UK.
 September 21  1981: Belize gains independence from the UK.
 September 21  1989: Hurricane Hugo slams South Carolina.
 September 21  1991: Armenia regains its independence from the Soviet Union.
 September 22  1908: Bulgarian independence is recognised.
 September 22  1960: Mali becomes independent.
 September 23  63 BC: Roman Emperor Augustus Caesar is born.
 September 23  1932: The Kingdom of Saudi Arabia is formed.
 September 23  2009: A major dust storm affects southeastern Australia, including Sydney.
 September 24  1853: France takes control of New Caledonia.
 September 24  1973: Guinea-Bissau declares independence from Portugal.
 September 26  1907: New Zealand and Newfoundland are given Dominion status within the British Empire.
 September 27  1821: Mexico gains independence from Spain.
 September 27  1905: The equation E=mc squared is introduced.
 September 28  1978: Pope John Paul I dies just 33 days after being elected.
 September 28  1994: The car and passenger ferry Estonia sinks during stormy weather in the Baltic Sea.
 September 29  1829: London's Metropolitan Police Force is founded.
 September 29  1990: Washington National Cathedral is completed.
 September 29  2009: An earthquake and tsunamis off Samoa, American Samoa and Tonga kill 189 people.
 September 30  1938: The Munich Pact is signed.
 September 30  1955: American film star James Dean dies aged 24 in a car crash.
 September 30  1966: Bechuanaland becomes independent from the UK and changes its name to Botswana.
 September 30  2009: A strong earthquake off western Sumatra kills over 1,000 people.

Symbols and Trivia 

 September is one of the two months that never ends on the same day of the week as any other months within any calendar year. (May is the other)
 The birth stone for September is the sapphire, symbolising clear thinking. The birth flowers for the month are the forget-me-not, morning glory and aster.
 The Zodiac signs for September are Virgo (August 22  September 21) and Libra (September 22  October 21).
 If the months of the year were arranged in alphabetical order in the English language, September would come last.
 Also in the English language, September has the longest name of all the months of the year, with nine letters. Coincidentally, it is also the ninth month. September is the only month of the year in the English language to have as many letters in its name as its numeric calendar position.
 September is the first of four months in-a-row to have a name ending in "ber". (October, November and December are the other three)
 September 1 is the only day in September during a common year to start within the middle third of the calendar year.
 It is the least common month for birthdays among US Presidents, with one, William Howard Taft (September 15).
 Among Prime Ministers of Australia, September is the most common month for birthdays, with seven.