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Day redirects here. For the Bajoran Field Colonel, see Day Kannu.


A millennium was a period of one thousand years.

In 2000, Henry Janeway expressed his belief that he'd been born in the wrong millennium. (VOY: "11:59")

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A century was a period of one hundred rotations around the sun.

Human and Vulcan centuries were not equivalent to Lactran centuries. (TAS: "The Eye of the Beholder")

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Decade Edit

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A decade was a period of ten years.

According to Trip Tucker in the mirror universe, a Human lost a decade off their life expectancy for every year spent working near a warp core. (ENT: "In a Mirror, Darkly")

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Year Edit

A year was the amount of time it took for a planet to orbit its sun. If the planet had an axial tilt, this resulted in seasons, like winter, spring, summer, and fall.

Vulcan year: In Gene Roddenberry's novelization of The Motion Picture he indicated that nine Vulcan seasons were equal to 2.8 Earth years. This would make Vulcan's year 456 ± 33 Earth days long.
The term "turn", used in the episode "Sins of the Father", was, according to the Star Trek Encyclopedia (3rd ed., p. 528), "the English translation of the Klingon term for year, as in one turn (or revolution) of a planet around its sun."

With a warp three engine, a cargo freighter could cut down a five year cargo run down to six months. (ENT: "Fortunate Son")

Nausicaan pirates were attacking freighters in a specific sector for years until 2151. (ENT: "Fortunate Son")

Standard UFP solar year Edit

Standard UFP solar years were mentioned in the Treaty of Armens. (TNG: "The Ensigns of Command", okudagram)

Earth year Edit

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One Earth year was equal to 365.2425 Earth days in the Gregorian calendar. To compensate for the fraction of a day, a leap day was added to every year whose number was divisible by four, unless it was a century, unless it was divisible by 400. These leap years consisted of adding an extra day to the month of February. Instead of the usual 28 days, there would be 29.

Scientists usually used a Julian year of 365.25 days for measurements and scientific comparisons.

According to Doctor Phlox, Travis Mayweather was twenty-six Earth years during his autopsy in 2152. (ENT: "Dead Stop")

The mean solar year was 365.242190419 days in 2000 AD, and will be shorter still by the 23rd century.
There was a reference to "terrestrial years" in dialogue in the revised final draft script of TOS: "The Conscience of the King". In the final version of that episode, however, this reference doesn't include the term "terrestrial".

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Month Edit

A month was usually the amount of time it took for a moon to orbit its planet. This was usually a portion of a year, and a large number of days (in which case it may be broken down into weeks).

On planets without moons, a month could either A) not exist, B) be equal to a season, or C) be a fractional division of a season. For example, Vulcan "has no moon", so it is unknown what portion of a year is represented by the "month" of Tasmeen. The novelization of The Motion Picture could be read to imply that Vulcan's "months" are whole seasons.

On Earth a month was originally the length of the lunar cycle (29.53 days). Most calendars at some point made the month one twelfth of a solar year (30.44 days). In Earth's most common calendar, the months are either 30 or 31 days long, with one shorter month (February) having 28 or 29 days depending on the year.

In August of 2151, Matthew Ryan told Travis Mayweather he ate his last steak eighteen months ago. (ENT: "Fortunate Son")

On an uninhabited planet it only gets night four days a month due to its binary stars. (ENT: "The Catwalk")

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A fortnight was a period of time lasting two weeks (14 days).

In 2376, Seamus claimed that Timothy Ryan had been dead for a fortnight. (VOY: "Fair Haven")

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A week was small number days grouped together as part of a calendar system. It could be a portion of a month or an unrelated grouping.

On Earth a week was seven days.

Seven days was a close approximation to one fourth of a lunar month. When months became one twelfth of a solar year the connection was broken, and one month was now about 4.35 weeks long.

In August of 2151, Enterprise NX-01 was sent to assist the Earth Cargo Service freighter ECS Fortunate as the nearest Starfleet vessel would need three weeks to arrive but Enterprise would only need one day and a half at maximum warp. (ENT: "Fortunate Son")

Takret only needed to sleep once a week. (ENT: "The Catwalk")

Travis Mayweather and his father once took shelter in the ship's core to protect against a class 3 neutronic storm. They were there for six weeks. (ENT: "The Catwalk")

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Day Edit

A day was the amount of time it takes for a planet to spin once on its own axis. This resulted in a day/night cycle (with day in this second case meaning the sunlit portion of the full day).

On Earth, a full day was divided up into twenty-four hours, whereas on Deep Space 9, a full day was divided into twenty-six hours. (DS9: "Afterimage")

Doctor Phlox estimated that the treatment of Captain Jackson Keene by using cortical regeneration would last two days, maybe three. Enterprise NX-01 was sent to assist the ECS Fortunate as it was the nearest and fastest Starfleet ship, at maximum warp at the scene in one day and a half. (ENT: "Fortunate Son")

On an uninhabited planet that Enterprise NX-01 explored in 2152, night was only available on four days a month due to the planet's binary stars. (ENT: "The Catwalk")

In 2263 of the alternate reality, USS Enterprise Captain James T. Kirk told Doctor Leonard McCoy, shortly after Kirk returned from an unsuccessful away mission to the planet Teenax, that it was "just another day in the fleet." Kirk subsequently made a log entry in which he reported that the Enterprise was on its 966th day in deep space, and that telling where one day ended and the next one began was increasingly difficult. This was around a couple of days before his thirtieth birthday. (Star Trek Beyond)

A day was divided into time units including morning, afternoon, evening, and night. Midnight was a specific time on a day. (ENT: "The Catwalk"; DS9: "The Nagus", "The Storyteller", "Defiant"; VOY: "Resistance")

Vice admiral Maxwell Forrest called Captain Jonathan Archer at four in the morning on one day in August of 2151. As Archer assumed not to talk about the data of Archer's Comet but to call Enterprise back to assist the ECS Fortunate. (ENT: "Fortunate Son")

Standard UFP solar day Edit

Standard UFP solar days were mentioned in the Treaty of Armens. (TNG: "The Ensigns of Command", okudagram)

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Hour Edit

An hour was a portion of a day, this could be a decimal tenth of a day, or some other fractional portion of a day.

On Earth an hour was an SI unit of time that was approximately 1/24 of a day, and was divided up into 60 minutes.

Though never fully explained on screen, Deep Space Nine episodes continue to refer to days in 26 hour cycles.

A chasm on the surface of Archer's Comet needed less than an hour to recrystallize when moving out of direct sunlight. (ENT: "Breaking the Ice")

A shapeshifter had to regenerate after sixteen hours in solid form. (DS9: "The Forsaken")

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Minute Edit

A minute was a portion of an hour, this could be a decimal hundredth of an hour, or some other fractional portion of an hour.

On Earth a minute was 1/60 of an hour, and was divided up into 60 seconds.

A common Earth slang was the question, "Do you have a minute?" (ENT: "Fortunate Son")

Commander Trip Tucker needed fourty minutes to synthesize new valve seals. (ENT: "Fortunate Son")

In colloquial speech, a minute can also mean an undefined short amount of time, as in "I'll be just a minute". (DS9: "Playing God")

The crew of Enterprise NX-01 would be dead within three minutes when exposed to the radiolytic isotopes of a neutronic storm. (ENT: "The Catwalk")

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Second Edit

A second was a portion of a minute, this could be a decimal hundredth of a minute, or some other fractional portion of a minute.

On Earth a second was 1/60 of a minute, and was usually divided up decimally.

The second is now precisely defined based on the atomic behavior of cesium, and the lengths of minutes, hours, and days are now defined in these seconds. This means that these other times are no longer exactly the same as their solar equivalents based on actual planetary motion.

Matthew Ryan told Travis Mayweather, he heard that for a split second you can actually feel yourself in both places at once during the use of a transporter. (ENT: "Fortunate Son")

Taking a neural toxin would kill the Denobulan Phlox in only a few seconds. (ENT: "Regeneration")

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Nanosecond Edit

A nanosecond was one billionth of a second.

In 2365, the USS Yamato was destroyed by a plasma vent that lasted T+2.25 nanoseconds. (TNG: "Contagion")

To attract the attention of the Crystalline Entity, the USS Enterprise-D emitted five-nanosecond graviton emissions at one pulse per second. (TNG: "Silicon Avatar")

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Main article: Stardate

In the 23rd century, stardates were not directly related to Earth's calendar. Beginning in 2323, stardates were changed to be 1,000 per Earth year.

The measurement of 1,000 stardate units per year was never explicitly stated on-screen, but can be inferred from numerous conversations. There are some apparent errors, or variations, however, in stardate calculation. One example is Annika Hansen's birth date being given as stardate 25479, and the year being given as 2350. If that is counted back, it would give the beginning year of 24th century stardates as 2325, which contradicts the Star Trek Chronology.
It is unknown exactly how many days are equal to 1,000 stardate units in the 24th century; it could be 365.25, 365.2425, or just 365.