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April is the fourth month of the year in the Gregorian calendar, the fifth in the early Julian, the first of four months to have a length of 30 days, and the second of five months to have a length of less than 31 days.

April is commonly associated with the season of autumn in parts of the Southern Hemisphere, and spring in parts of the Northern Hemisphere, where it is the seasonal equivalent to October in the Southern Hemisphere and vice versa.

December is the twelfth and final month of the year in the Julian and Gregorian calendars. It is also the last of seven months to have a length of 31 days.

December got its name from the Latin word decem (meaning ten) because it was originally the tenth month of the year in the calendar of Romulus c. 750 BC which began in March. The winter days following December were not included as part of any month. Later, the months of January and February were created out of the monthless period and added to the beginning of the calendar, but December retained its name.

In Ancient Rome, as one of the four Agonalia, this day in honour of Sol Indiges was held on December 11, as was Septimontium. Dies natalis (birthday) was held at the temple of Tellus on December 13, Consualia was held on December 15, Saturnalia was held December 17–23, Opiconsivia was held on December 19, Divalia was held on December 21, Larentalia was held on December 23, and the dies natalis of Sol Invictus was held on December 25. These dates do not correspond to the modern Gregorian calendar.

The Anglo-Saxons referred to December–January as Ġēolamonaþ (modern English: "Yule month"). The French Republican Calendar contained December within the months of Frimaire and Nivôse.

September is the ninth month of the year in the Julian and Gregorian calendars, the third of four months to have a length of 30 days, and the fourth of five months to have a length of fewer than 31 days. September in the Northern Hemisphere and March in the Southern Hemisphere are seasonal equivalent.

In the Northern hemisphere, the beginning of the meteorological autumn is on 1 September. In the Southern hemisphere, the beginning of the meteorological spring is on 1 September.　

September marks the beginning of the ecclesiastical year in the Eastern Orthodox Church. It is the start of the academic year in many countries of the northern hemisphere, in which children go back to school after the summer break, sometimes on the first day of the month.

September (from Latin septem, "seven") was originally the seventh of ten months in the oldest known Roman calendar, the calendar of Romulus c. 750 BC, with March (Latin Martius) the first month of the year until perhaps as late as 451 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.

March is the third month of the year in both the Julian and Gregorian calendars. It is the second of seven months to have a length of 31 days. In the Northern Hemisphere, the meteorological beginning of spring occurs on the first day of March. The March equinox on the 20 or 21 marks the astronomical beginning of spring in the Northern Hemisphere and the beginning of autumn in the Southern Hemisphere, where September is the seasonal equivalent of the Northern Hemisphere's March.

November is the eleventh and penultimate month of the year in the Julian and Gregorian Calendars, the fourth and last of four months to have a length of 30 days and the fifth and last of five months to have a length of fewer than 31 days. November was the ninth month of the calendar of Romulus c. 750 BC. November retained its name (from the Latin novem meaning "nine") when January and February were added to the Roman calendar.November is a month of late spring in the Southern Hemisphere and late autumn in the Northern Hemisphere. Therefore, November in the Southern Hemisphere is the seasonal equivalent of May in the Northern Hemisphere and vice versa. In Ancient Rome, Ludi Plebeii was held from November 4–17, Epulum Jovis was held on November 13 and Brumalia celebrations began on November 24. These dates do not correspond to the modern Gregorian calendar.

November was referred to as Blōtmōnaþ by the Anglo-Saxons. Brumaire and Frimaire were the months on which November fell in the French Republican Calendar.

January is the first month of the year in the Julian and Gregorian calendars and the first of seven months to have a length of 31 days. The first day of the month is known as New Year's Day. It is, on average, the coldest month of the year within most of the Northern Hemisphere (where it is the second month of winter) and the warmest month of the year within most of the Southern Hemisphere (where it is the second month of summer). In the Southern hemisphere, January is the seasonal equivalent of July in the Northern hemisphere and vice versa.

Ancient Roman observances during this month include Cervula and Juvenalia, celebrated January 1, as well as one of three Agonalia, celebrated January 9, and Carmentalia, celebrated January 11. These dates do not correspond to the modern Gregorian calendar.

July is the seventh month of the year (between June and August) in the Julian and Gregorian calendars and the fourth of seven months to have a length of 31 days. It was named by the Roman Senate in honour of Roman general Julius Caesar, it being the month of his birth. Before that, it was called Quintilis, being the fifth month of the 10-month calendar.

It is on average the warmest month in most of the Northern Hemisphere, where it is the second month of summer, and the coldest month in much of the Southern Hemisphere, where it is the second month of winter. The second half of the year commences in July. In the Southern Hemisphere, July is the seasonal equivalent of January in the Northern hemisphere.

"Dog days" are considered to begin in early July in the Northern Hemisphere, when the hot sultry weather of summer usually starts. Spring lambs born in late winter or early spring are usually sold before 1 July.

May is the fifth month of the year in the Julian and Gregorian calendars and the third of seven months to have a length of 31 days.

May is a month of spring in the Northern Hemisphere and autumn in the Southern Hemisphere. Therefore, May in the Southern Hemisphere is the seasonal equivalent of November in the Northern Hemisphere and vice versa. Late May typically marks the start of the summer vacation season in the United States (Memorial Day) and Canada (Victoria Day) that ends on Labor Day, the first Monday of September.

May (in Latin, Maius) was named for the Greek Goddess Maia, who was identified with the Roman era goddess of fertility, Bona Dea, whose festival was held in May. Conversely, the Roman poet Ovid provides a second etymology, in which he says that the month of May is named for the maiores, Latin for "elders," and that the following month (June) is named for the iuniores, or "young people" (Fasti VI.88).

Mayovka, in the context of the late Russian Empire, was a picnic in the countryside or in a park in the early days of May, hence the name. Eventually, "mayovka" (specifically, "proletarian mayovka") came to mean an illegal celebration of May 1 by revolutionary public, typically presented as an innocent picnic.

Special devotions to the Virgin Mary take place in May. See May devotions to the Blessed Virgin Mary.

Eta Aquariids meteor shower appears in May. It is visible from about April 21 to about May 20 each year with peak activity on or around May 6. The Arietids shower from May 22 – July 2, and peaks on June 7. The Virginids also shower at various dates in May.

August is the eighth month of the year in the Julian and Gregorian calendars, and the fifth of seven months to have a length of 31 days. Its zodiac sign is Leo and was originally named Sextilis in Latin because it was the 6th month in the original ten-month Roman calendar under Romulus in 753 BC, with March being the first month of the year. About 700 BC, it became the eighth month when January and February were added to the year before March by King Numa Pompilius, who also gave it 29 days. Julius Caesar added two days when he created the Julian calendar in 46 BC (708 AUC), giving it its modern length of 31 days. In 8 BC, it was renamed in honor of Emperor Augustus. According to a Senatus consultum quoted by Macrobius, he chose this month because it was the time of several of his great triumphs, including the conquest of Egypt. Commonly repeated lore has it that August has 31 days because Augustus wanted his month to match the length of Julius Caesar's July, but this is an invention of the 13th century scholar Johannes de Sacrobosco. Sextilis in fact had 31 days before it was renamed, and it was not chosen for its length.

In the Southern Hemisphere, August is the seasonal equivalent of February in the Northern Hemisphere. In the Northern Hemisphere, August falls in the season of summer. In the Southern Hemisphere, the month falls during the season of winter. In many European countries, August is the holiday month for most workers. Numerous religious holidays occurred during August in ancient Rome.

Certain meteor showers take place in August. The Kappa Cygnids take place in August, with the dates varying each year. The Alpha Capricornids meteor shower takes place as early as July 10 and ends at around August 10, and the Southern Delta Aquariids take place from mid-July to mid-August, with the peak usually around July 28–29. The Perseids, a major meteor shower, typically takes place between July 17 and August 24, with the days of the peak varying yearly. The star cluster of Messier 30 is best observed around August.

Among the aborigines of the Canary Islands, especially among the Guanches of Tenerife, the month of August received in the name of Beñesmer or Beñesmen, which was also the harvest festival held this month.

October is the tenth month of the year in the Julian and Gregorian calendars and the sixth of seven months to have a length of 31 days. The eighth month in the old calendar of Romulus c. 750 BC, October retained its name (from the Latin and Greek ôctō meaning "eight") after January and February were inserted into the calendar that had originally been created by the Romans. In Ancient Rome, one of three Mundus patet would take place on October 5, Meditrinalia October 11, Augustalia on October 12, October Horse on October 15, and Armilustrium on October 19. These dates do not correspond to the modern Gregorian calendar. Among the Anglo-Saxons, it was known as Ƿinterfylleþ, because at this full moon (fylleþ) winter was supposed to begin.

October is commonly associated with the season of spring in parts of the Southern Hemisphere, and autumn in parts of the Northern Hemisphere, where it is the seasonal equivalent to April in the Southern Hemisphere and vice versa.

February is the second month of the year in the Julian and Gregorian calendars. The month has 28 days in common years or 29 in leap years, with the 29th day being called the leap day. It is the first of five months not to have 31 days (the other four being April, June, September, and November) and the only one to have fewer than 30 days.

February is the third and last month of meteorological winter in the Northern Hemisphere. In the Southern Hemisphere, February is the third and last month of meteorological summer (being the seasonal equivalent of what is August in the Northern Hemisphere).