What is the length of the Vulcan year?
Nobody knows, as far as I know.
However, Vulcan has a sun according to "Operation - Annihlate!"
A sun is an equivalent of Earth's sun, a star close enough to a planet to illuminate and heat it, and usually close enough to appear as a visible disc in the sky of the planet instead of appearing as a mere dimensionless dot in the sky of the planet.
Therefore, Vulcan, being close enough to a star to be warmed by it, must oribt around at least one star, and possibly orbit around two or more stars which are much closer together than the distance between them and Vulcan. Vulcan can either orbit directly around its star(s) or else orbit around some object which orbits around that star, an object like another planet, a brown dwarf, or possibly a star too dim to give Vulcan as much heat and light as the more distance star that is Vulcan's sun.
Since Vulcan must orbit around at least one star, it has an orbital period, which would be a year of Vulcan. Though of course it is possible that the length of the period called a year in a Vulcan calendar could be significantley longer or shorter than its orbital period for some reason.
There is very little evidence of the Vulcan clanendar and time keepling system. In many Star Trek productions Vulcans mentioned years, months, or days, but it is unknown whether they mean Vulcan time units or are using Earth time units, or hypothetical Starfleet, hypothetical Federation, or hypothetical Galactic Standard time units. And it is unkown whether when Vulcans mention time spans in Vulcan time units those are translated into Earth time units for the benefit of the audience.
In Star Trek VI: The Undiscovered Country Captain Sulu of the Excelsior is mkaing a long entry when the klingon moon Praxis explodes.
In a later meeting at Starfleeet Headquarters Spock says.
Two Earth months l seem like areasonable time span for Spock to have initiated diplomatic discussions with the Klingons. During this meeting Kirk also says:
Sometime after the meeting Kirk makes a log entry:
So apparently two months have passed and the stardate got only 1.0 stardate units higher. This indicates that in that era there is aratio of about 0.5 stardate units per month.
After some adventures which may take days or weeks or maybe months the last line in the movie is:
So this is about 7.5 stardate units after the beginning of the movie and about 6.5 stardate units after Kir's first log. At about 0.5 stardate units per month, that is about 13 months after Kirk's earlier log and15 months after Sulu's log at the beginning of the movie. But fi the movie takes less than the three months until Kirk and his senior staff are due to reture, then there would be less than four months in about 6.5 stadate units, or less than 0.6153 (zero point six one five three) months per stardate unit. At a ratio of 0.6153 months per stardate unit, one stardate unit would equal about 1.625 (one point six two five) months. So that fits fairly well.
In the Voyager episode "Flashback", there are flashbacks to events on the starship Excelsior during Star Trek VI: The Undiscovered Country.
I thought that Tuvok said that two days had passed since Excelsior detected the explosion of Praxis. If the stardate is still 9521, days after Sulu said it was stardate 9521.6, there must be fewer than 0.4 stardate units in the two or three days since the explosion of Praxis and thus the ratio of days per stardate unit must be 0.1333 to 0.2, or lower.
If three days (two to four) equal two months (one to three) then there should be about 0.6666 to 4 days in a month. thus it is possible that Spock and Tuvok used tiem units from different planets in their statements. Possibly there are about 0.6666 to 4 Vulcan days in an Earth month, making an Vulcan day equal about t7.5 to 45 Earth days. But if Spock mentioned some other type of months instead of Earth months in star Trek VI: The Undiscovered Country the rleatioon ship between Vulcan days and Earth days would be unkown.
Or posssibly Spack and Tuvok used the same time unit which was translated for Earth audiences as "month" in Star Trek VI: The Undiscovered Country and as "day" in "Flashback".
For example, if Vulcan was a planet sized exomoon of a giant exoplanet, tidal locking would slow down the roatation of Vulcan until Vulcan was tidally locked to the planet.so that one side of Vulcan always faced the giant planet and the other side always faced away from it. Thus the "day" on Vulcan, the period between two successive sunrises, would equal the month Vulcan, the length of Vuclan's orrbit around its planet.
Since the orbital period of a planet sized exomoon around its griant exoplanet might last between about 1.5 to 15 Earth days, it would be possible for Vulcan to have a day/month between about 7.5 and 45 Earth days long.
But as Timo pointed out in another thread, the Vulcan month of Tasmeen has at least twenty days, so Vulcan can't have month and a day of the same length.
Fans have often wondered about the large orbs seen in the Vulcan sky in various productions. Any particular orb seen in the Vulcan sky either was gravitationally bound to Vulcan or was not. If an world was gravitationally bound to Vulcan, it could be a moon of Vulcan, or the other planet in a double planet with Vulcan, or else it could be the planet which Vulcan orbited as a moon.
In the TOS episode "The Man Trap" Uhura and Spock have a discussion:
So that seems to make it impossible for any of the orbs seen in the Vulcan sky to be a moon of Vulcan.
If Vulcan and one of the orbs seen in the sky are sister planets of roughly similar size and mass forming a double planet, Vulcan would probably be tidally locked to the sister planet. Thus the Vulcan day would equal the length of one complete orbital peirod of the two planets around their common center of mass.
And it is pssible, though unlikely, that the two planets would be close enough that their orbital period, and thus the day of Vulcan, would be about one to two Earth days long.
What about when two orbs are seen in the Vulcan sky at the same time? The smaller orb could be a moon of the other planet in the double planet. It would be rather improbable, though not impossible, for one of the planets in a double planet to have a moon in a stable orbit.
Or maybe the smaller orb could be a moon that orbits both planets in the double planet at several times the distance that they orbit around their common center. Just a a triple star often has two stars that orbit each other closely and a third star which orbits farther away.
And the "planet" Vulcan could actually be a giant, planet sized moon of a giant planet. Thus the other orbs seen the Vulcan sky could be other large moons of the giant planet. One or more might obit the giant planet farther out than Vulcan did, but at least one would orbit the giant planet closer than Vulcan did, since most editions of Star Trek: The Motion Picture have a scene where a smaller astronomical object passes in front of a larger astronomical orbject.. The larger astronomical object would be the giant planet which Vulcan orbits and the smaller astronomical object would presumably be another moon orbiting closer to the giant planet.
There is one other possibility for the smaller astronomical object passing in front of the larger one. This little script describes what it might be. The is at Vulcan for resupply, and Spock is down on Vulcan on business one night when Uhura accosts him"
Uhura: "Spock! There you are!"
Spock: Yes. You seem upset, Lieutenant."
Uhura: "Damn right I'm upset! We've been at Vuclan for a couple of days, and I didn't bother to come down with my boyfriend because I thought Vulcan wasn't a romantic place to visit, even since you lied and said that Vulcan has no moon!
spock: Vulcan has no moon, Miss Uhura.
Uhura (pointing at the sky): What's that? I could have enjoyed a romantic evening with a friend, but you said that Vulcan has no moon!
Spock: That is T'Khut. T'khut is not a moon, it is a giant planet that Vulcan orbits, thus making Vulcan a moon.
Uhura: Arggh! Why are you so pedantic? I could have enjoyed a romantic night just as well by planet light as by moon light. So what is that smaller object, another moon of T'Khut?
Spock: No. TMhut is not a moon, it orbits around Vulcan.
Uhura: So T'Mhut is a moon of Vulcan! You lied.
Spock: According to planetary science definitions, any object large enough to have a spheriodal shape counts as a planet. Thus "Tkhut, Vulcan, and T'Mhut are all planets according to Planetary science. According to astronomical definitions, T'Khut is a planet because it orbits a star, Vulcan is a moon because it orbits the planet T'Khut, and T'Mhut is a moon of a moon or a submoon because it orbits the moon Vulcan. So T'Mhut is not a moon by either definition.
Uhura drops to her knees and pounds on the ground.
Uhura: Aaaash!
Passing Vulcan child: She is emotional, isn't she.
A subsatelllite or submoon or moonmoon is possible but rather unlikely to have a stable orbit.
https://en.wikipedia.org/wiki/Subsatellite
Since Vulcan has no moon, a Vulcan month could not be the orbital period of a moon around Vulcan. But possibly the synodic period for the orbits of Vulcan and another moon of a giant planet to line up in the same configuration again might be a period in the Vulcan calendar that could be translated as a month.
Gene Roddenberry and D.C. Fontana wrote "No Moon" on a sketch of Vulcan for the TAS epiosode "Yesteryear", but the artists depicted a moon like object in the Vuclan sky anyway. If Roddenberry and Fontana didn't want Vulcan to have a moon, why did Fontana write in the script - and Roddenberry accept - mention of a Vulcan month?
Maybe they forgot that without a moon, Vulcan couldn't have a month like Earth does. Or maybe they decided that the Vulcan calendar divided the Vulcan year into periods that translated into Engish as months, even though they had nothing to do with the orbit of any moon around Vuclan.
In "Yesteryear" years are mentioned several times, but the type of year is specified only once. Use of the Guardian of forever accidentially causes Spock to die aged seven years of an unspecified type.
That happened twenty to thirty Vulcan years earlier.
So in "Yesteryear" Spock should be aged twenty to thirty Vulcan years plus seven Vulcan or Earth or other years.
And the Vuclan calendar has months, and at least one Vulcan month, Tasmeen, has at least twnty days.
Spock goes back in time to rescue his younger self, telling the Guardian of Forever:
So Tasmeen is definitly translated as a month and not has a season, depite Vulcan not having a moon.
If the Guardian sent Spock thirty Vulcan years into the past, Spock would be aged thirty Vulcan years plus seven years of unspecified type, possibly Vulcan or Earth years.
Note that Dorothy Fontana's script for "Journey to Babel" had a description of Amanda as being 58 years, and The Making of Star Trek, 1968, describes Amanda as 58 years old, and Doroth Fontana's script for "Yesteryear" describes Amanda as being thirty when Spocks goes thirty years in the past. Anyway, Amanda doesn't look terribly old in "Journey to Babel"
On the other hand, Spock could not be too young in TOS since "The Menagerie" is thirteen yeas after the mission to Talos IV, when Spock was already senior enough to be third in command of the Enterprise.
So Spock should be about thirty five to forty during TOS. And if Spock's age in Vulcan years is about thirty seven in "Yesteryear", that would mean that Vulcan years are approximately as long as Earth years.
If Spock went back in tieme thirty Earth years to a period in the time span of twenty to thirty Vulcan years past, that would make a Vulcan year about 0.967 (zero point nine six seven) to 1.55 (one point five five zero) Earth years long. Or approximately 353.196 (three hundred fifty three point one nine six) to 566.137 (five hundred sixty three point one three seven).Earth days.
I think that is all the evidence for the length of Vulcan years in Star Trek canon. Humans who travel to Vulcan comment on the heat and the thin air. In Amok time:
And when Spock is affected by a rapid aging conditionin "The Deadly Years":
But apparently nobody comments on the length of Vulcan days, months, years, or other time periods.
Of course there are some references to the length of Vulcanyears in non canon sources.
Another piece of evidence for the length of the Vulcan year is Gene Roddenberry's novelization of Star Trek: The Motion Picture .
IN Chapter Two, Spock is on the plateau of Gol, undergoing Kolinahr to purge him of all emotions.
This claims that Vulcan is in a double or multiple star system.
And a note explains:
Nobody would write nine seasonws if the actualy time wa less than eight or more than ten seasons. Nobody wouuld write 2.8 years if the actual time was less than 2.7 years or more than 2.9. Therefore.a Vulcan season should be between 0.27 (zero point two seven) and 0.3625 (zero point three six two five) Earth years long.
On Earth, the meteorological season in different places can vary in number and duration. But there are four astronomical seasons of equal length,
If Vulcan also has four astronomical seasons of equal length in a Vulcan year, a Vulcan year should equal 1.08 (one point zero eight) to 1.45 (one point four five) Earth years, or approximately 394.47 (three hundred ninety four point four seven) to 529.6125 (five hundred twenty nine point six one two five) Earth days.
So I wonder whether anyone can think of any other canon or non canon evidence for the length of Vulcan years.
Nobody knows, as far as I know.
However, Vulcan has a sun according to "Operation - Annihlate!"
A sun is an equivalent of Earth's sun, a star close enough to a planet to illuminate and heat it, and usually close enough to appear as a visible disc in the sky of the planet instead of appearing as a mere dimensionless dot in the sky of the planet.
Therefore, Vulcan, being close enough to a star to be warmed by it, must oribt around at least one star, and possibly orbit around two or more stars which are much closer together than the distance between them and Vulcan. Vulcan can either orbit directly around its star(s) or else orbit around some object which orbits around that star, an object like another planet, a brown dwarf, or possibly a star too dim to give Vulcan as much heat and light as the more distance star that is Vulcan's sun.
Since Vulcan must orbit around at least one star, it has an orbital period, which would be a year of Vulcan. Though of course it is possible that the length of the period called a year in a Vulcan calendar could be significantley longer or shorter than its orbital period for some reason.
There is very little evidence of the Vulcan clanendar and time keepling system. In many Star Trek productions Vulcans mentioned years, months, or days, but it is unknown whether they mean Vulcan time units or are using Earth time units, or hypothetical Starfleet, hypothetical Federation, or hypothetical Galactic Standard time units. And it is unkown whether when Vulcans mention time spans in Vulcan time units those are translated into Earth time units for the benefit of the audience.
In Star Trek VI: The Undiscovered Country Captain Sulu of the Excelsior is mkaing a long entry when the klingon moon Praxis explodes.
In a later meeting at Starfleeet Headquarters Spock says.
Two Earth months l seem like areasonable time span for Spock to have initiated diplomatic discussions with the Klingons. During this meeting Kirk also says:
Sometime after the meeting Kirk makes a log entry:
So apparently two months have passed and the stardate got only 1.0 stardate units higher. This indicates that in that era there is aratio of about 0.5 stardate units per month.
After some adventures which may take days or weeks or maybe months the last line in the movie is:
So this is about 7.5 stardate units after the beginning of the movie and about 6.5 stardate units after Kir's first log. At about 0.5 stardate units per month, that is about 13 months after Kirk's earlier log and15 months after Sulu's log at the beginning of the movie. But fi the movie takes less than the three months until Kirk and his senior staff are due to reture, then there would be less than four months in about 6.5 stadate units, or less than 0.6153 (zero point six one five three) months per stardate unit. At a ratio of 0.6153 months per stardate unit, one stardate unit would equal about 1.625 (one point six two five) months. So that fits fairly well.
In the Voyager episode "Flashback", there are flashbacks to events on the starship Excelsior during Star Trek VI: The Undiscovered Country.
I thought that Tuvok said that two days had passed since Excelsior detected the explosion of Praxis. If the stardate is still 9521, days after Sulu said it was stardate 9521.6, there must be fewer than 0.4 stardate units in the two or three days since the explosion of Praxis and thus the ratio of days per stardate unit must be 0.1333 to 0.2, or lower.
If three days (two to four) equal two months (one to three) then there should be about 0.6666 to 4 days in a month. thus it is possible that Spock and Tuvok used tiem units from different planets in their statements. Possibly there are about 0.6666 to 4 Vulcan days in an Earth month, making an Vulcan day equal about t7.5 to 45 Earth days. But if Spock mentioned some other type of months instead of Earth months in star Trek VI: The Undiscovered Country the rleatioon ship between Vulcan days and Earth days would be unkown.
Or posssibly Spack and Tuvok used the same time unit which was translated for Earth audiences as "month" in Star Trek VI: The Undiscovered Country and as "day" in "Flashback".
For example, if Vulcan was a planet sized exomoon of a giant exoplanet, tidal locking would slow down the roatation of Vulcan until Vulcan was tidally locked to the planet.so that one side of Vulcan always faced the giant planet and the other side always faced away from it. Thus the "day" on Vulcan, the period between two successive sunrises, would equal the month Vulcan, the length of Vuclan's orrbit around its planet.
Since the orbital period of a planet sized exomoon around its griant exoplanet might last between about 1.5 to 15 Earth days, it would be possible for Vulcan to have a day/month between about 7.5 and 45 Earth days long.
But as Timo pointed out in another thread, the Vulcan month of Tasmeen has at least twenty days, so Vulcan can't have month and a day of the same length.
Fans have often wondered about the large orbs seen in the Vulcan sky in various productions. Any particular orb seen in the Vulcan sky either was gravitationally bound to Vulcan or was not. If an world was gravitationally bound to Vulcan, it could be a moon of Vulcan, or the other planet in a double planet with Vulcan, or else it could be the planet which Vulcan orbited as a moon.
In the TOS episode "The Man Trap" Uhura and Spock have a discussion:
So that seems to make it impossible for any of the orbs seen in the Vulcan sky to be a moon of Vulcan.
If Vulcan and one of the orbs seen in the sky are sister planets of roughly similar size and mass forming a double planet, Vulcan would probably be tidally locked to the sister planet. Thus the Vulcan day would equal the length of one complete orbital peirod of the two planets around their common center of mass.
And it is pssible, though unlikely, that the two planets would be close enough that their orbital period, and thus the day of Vulcan, would be about one to two Earth days long.
What about when two orbs are seen in the Vulcan sky at the same time? The smaller orb could be a moon of the other planet in the double planet. It would be rather improbable, though not impossible, for one of the planets in a double planet to have a moon in a stable orbit.
Or maybe the smaller orb could be a moon that orbits both planets in the double planet at several times the distance that they orbit around their common center. Just a a triple star often has two stars that orbit each other closely and a third star which orbits farther away.
And the "planet" Vulcan could actually be a giant, planet sized moon of a giant planet. Thus the other orbs seen the Vulcan sky could be other large moons of the giant planet. One or more might obit the giant planet farther out than Vulcan did, but at least one would orbit the giant planet closer than Vulcan did, since most editions of Star Trek: The Motion Picture have a scene where a smaller astronomical object passes in front of a larger astronomical orbject.. The larger astronomical object would be the giant planet which Vulcan orbits and the smaller astronomical object would presumably be another moon orbiting closer to the giant planet.
There is one other possibility for the smaller astronomical object passing in front of the larger one. This little script describes what it might be. The is at Vulcan for resupply, and Spock is down on Vulcan on business one night when Uhura accosts him"
Uhura: "Spock! There you are!"
Spock: Yes. You seem upset, Lieutenant."
Uhura: "Damn right I'm upset! We've been at Vuclan for a couple of days, and I didn't bother to come down with my boyfriend because I thought Vulcan wasn't a romantic place to visit, even since you lied and said that Vulcan has no moon!
spock: Vulcan has no moon, Miss Uhura.
Uhura (pointing at the sky): What's that? I could have enjoyed a romantic evening with a friend, but you said that Vulcan has no moon!
Spock: That is T'Khut. T'khut is not a moon, it is a giant planet that Vulcan orbits, thus making Vulcan a moon.
Uhura: Arggh! Why are you so pedantic? I could have enjoyed a romantic night just as well by planet light as by moon light. So what is that smaller object, another moon of T'Khut?
Spock: No. TMhut is not a moon, it orbits around Vulcan.
Uhura: So T'Mhut is a moon of Vulcan! You lied.
Spock: According to planetary science definitions, any object large enough to have a spheriodal shape counts as a planet. Thus "Tkhut, Vulcan, and T'Mhut are all planets according to Planetary science. According to astronomical definitions, T'Khut is a planet because it orbits a star, Vulcan is a moon because it orbits the planet T'Khut, and T'Mhut is a moon of a moon or a submoon because it orbits the moon Vulcan. So T'Mhut is not a moon by either definition.
Uhura drops to her knees and pounds on the ground.
Uhura: Aaaash!
Passing Vulcan child: She is emotional, isn't she.
A subsatelllite or submoon or moonmoon is possible but rather unlikely to have a stable orbit.
https://en.wikipedia.org/wiki/Subsatellite
Since Vulcan has no moon, a Vulcan month could not be the orbital period of a moon around Vulcan. But possibly the synodic period for the orbits of Vulcan and another moon of a giant planet to line up in the same configuration again might be a period in the Vulcan calendar that could be translated as a month.
Gene Roddenberry and D.C. Fontana wrote "No Moon" on a sketch of Vulcan for the TAS epiosode "Yesteryear", but the artists depicted a moon like object in the Vuclan sky anyway. If Roddenberry and Fontana didn't want Vulcan to have a moon, why did Fontana write in the script - and Roddenberry accept - mention of a Vulcan month?
Maybe they forgot that without a moon, Vulcan couldn't have a month like Earth does. Or maybe they decided that the Vulcan calendar divided the Vulcan year into periods that translated into Engish as months, even though they had nothing to do with the orbit of any moon around Vuclan.
In "Yesteryear" years are mentioned several times, but the type of year is specified only once. Use of the Guardian of forever accidentially causes Spock to die aged seven years of an unspecified type.
That happened twenty to thirty Vulcan years earlier.
So in "Yesteryear" Spock should be aged twenty to thirty Vulcan years plus seven Vulcan or Earth or other years.
And the Vuclan calendar has months, and at least one Vulcan month, Tasmeen, has at least twnty days.
Spock goes back in time to rescue his younger self, telling the Guardian of Forever:
So Tasmeen is definitly translated as a month and not has a season, depite Vulcan not having a moon.
If the Guardian sent Spock thirty Vulcan years into the past, Spock would be aged thirty Vulcan years plus seven years of unspecified type, possibly Vulcan or Earth years.
Note that Dorothy Fontana's script for "Journey to Babel" had a description of Amanda as being 58 years, and The Making of Star Trek, 1968, describes Amanda as 58 years old, and Doroth Fontana's script for "Yesteryear" describes Amanda as being thirty when Spocks goes thirty years in the past. Anyway, Amanda doesn't look terribly old in "Journey to Babel"
On the other hand, Spock could not be too young in TOS since "The Menagerie" is thirteen yeas after the mission to Talos IV, when Spock was already senior enough to be third in command of the Enterprise.
So Spock should be about thirty five to forty during TOS. And if Spock's age in Vulcan years is about thirty seven in "Yesteryear", that would mean that Vulcan years are approximately as long as Earth years.
If Spock went back in tieme thirty Earth years to a period in the time span of twenty to thirty Vulcan years past, that would make a Vulcan year about 0.967 (zero point nine six seven) to 1.55 (one point five five zero) Earth years long. Or approximately 353.196 (three hundred fifty three point one nine six) to 566.137 (five hundred sixty three point one three seven).Earth days.
I think that is all the evidence for the length of Vulcan years in Star Trek canon. Humans who travel to Vulcan comment on the heat and the thin air. In Amok time:
And when Spock is affected by a rapid aging conditionin "The Deadly Years":
But apparently nobody comments on the length of Vulcan days, months, years, or other time periods.
Of course there are some references to the length of Vulcanyears in non canon sources.
Another piece of evidence for the length of the Vulcan year is Gene Roddenberry's novelization of Star Trek: The Motion Picture .
IN Chapter Two, Spock is on the plateau of Gol, undergoing Kolinahr to purge him of all emotions.
This claims that Vulcan is in a double or multiple star system.
And a note explains:
Nobody would write nine seasonws if the actualy time wa less than eight or more than ten seasons. Nobody wouuld write 2.8 years if the actual time was less than 2.7 years or more than 2.9. Therefore.a Vulcan season should be between 0.27 (zero point two seven) and 0.3625 (zero point three six two five) Earth years long.
On Earth, the meteorological season in different places can vary in number and duration. But there are four astronomical seasons of equal length,
If Vulcan also has four astronomical seasons of equal length in a Vulcan year, a Vulcan year should equal 1.08 (one point zero eight) to 1.45 (one point four five) Earth years, or approximately 394.47 (three hundred ninety four point four seven) to 529.6125 (five hundred twenty nine point six one two five) Earth days.
So I wonder whether anyone can think of any other canon or non canon evidence for the length of Vulcan years.
Last edited:
One more take on Vulcan:
