Despite being related to the word "four" (4), 40 is spelled "forty", not "fourty". The reason is that etymologically (even in accents without the horse-hoarse merger), the words have different vowels, "forty" containing a contraction in the same way that "fifty" contains a contraction of "five". The letters of the word "forty" are in alphabetical order; this is the only number that has this linguistic property in English.
Negative forty is the temperature at which the Fahrenheit and Celsius scales correspond; that is, −40°F = −40°C. It is referred to as either "minus forty" or "forty below".
Astronomy
The planet Venus forms a pentagram in the night sky every eight years with it returning to its original point every 40 years with a 40 day regression (some scholars believe that this ancient information was the basis for the number 40 becoming sacred to Jews, Christians, and Muslims).
solar eclipse series which began on -1653 May 28 and ended on -373 July 4. The duration of Saros series 40 was 1280.1 years, and it contained 72 solar eclipses.
lunar eclipse series which began on -1387 February 12 and ended on -71 April 12. The duration of Saros series 40 was 1316.2 years, and it contained 74 lunar eclipses.
In religion
The number 40 is significant in Jewish, Christian, Islamic, and other Middle Eastern traditions. It can represent an estimate, or many of something.
Rain fell for "Forty days and forty nights" during Noah's flood
Spies explored the Promised Land for "Forty days." (Numbers 13)
Israel wandered in the wilderness for "Forty years". This period of years represents the time it takes for a new generation to arise.
Moses' life is divided into three 40-year segments, separated by his fleeing from Egypt, and his return to lead his people out.
Several Israelite leaders and kings are said to have ruled for "forty years", that is, a generation. (Examples: Eli, Saul, David, Solomon.)
Moses spent three consecutive periods of "forty days and forty nights" on Mount Sinai:
He went up on the seventh day of Sivan, after God gave the Torah to the Jewish people, in order to learn the Torah from God, and came down on the seventeenth day of Tammuz, when he saw the Jews worshiping the Golden Calf and broke the tablets
He went up on the eighteenth day of Tammuz to beg forgiveness for the people's sin and came down without God's atonement on the twenty-ninth day of Av
He went up on the first day of Elul and came down on the tenth day of Tishrei, the first Yom Kippur, with God's atonement
Amikvah consists of 40 se'ah (approximately 200 gallons) of water
40 lashes is one of the punishments meted out by the Sanhedrin, though in actual practice only 39 lashes were administered.
Jesus was presented at the Temple forty days after his birth.
Before the temptation of Christ, Jesus fasted "Forty days and forty nights" in the wilderness.
In modern Christian practice, Lent consists of the 40 days preceding Easter. In much of Western Christianity Sundays are excluded from the count; in Eastern Christianity Sundays are included.
The dead are usually mourned for forty days in Muslim cultures.
Masih ad-Dajjal roams around the Earth in forty days, a period of time that can be as many as forty months, forty years, and so on.[citation needed]
Khadijah was forty years old when she married Muhammad.
Muhammad was forty years old when he first received the revelation delivered by the archangel Gabriel.
The Quran says that a person is only fully grown when they reach the age of 40.
In the Yazidi faith, The Chermera temple (meaning “40 Men” in the Yazidi dialect) is so old that no one remembers how it came to have that name but it is believed to derive from the burial of 40 men on the mountaintop site.
Some Russians believe that ghosts of the dead linger at the site of their death for forty days.
InHinduism, some popular religious prayers consist of forty shlokasordohas (couplets, stanzas). The most common being the Hanuman Chalisa (chaalis is the Hindi term for 40).
In other fields
Forty is also:
To understand a people, you must live among them for 40 days. ~Arabic proverb[1][2]
the caliber of the bullet in the .40 S&W handgun cartridge
the A40 and M40, important highways in the UK. The A40 is a trunk road in England and Wales, connecting LondontoFishguard. The M40 motorway is the second motorway in the British transport network to connect London to Birmingham
In tennis, the number 40 represents the third point gained in a game. A score of 40-40 (three points each) is called "deuce", at which time a player must score two consecutive points to win the game.
In the song "Billie Jean" by Michael Jackson, the lyrics state that "For forty days and for forty nights / the law was on her side" in reference to the Genesis story of Noah.