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What's the reason that we have a different number of days each month?
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It always was interesting for me to understand the answer for the question:
What's the reason that we have a different number of days each month?
If the month is fixed on the time that the moon circles the earth, then the time of the circling isn't equal each month? And if the month fixed by the time that the earth circles the sun and then divided by 12 (365:12=30.4), why one month has more days and the other month has less days?
Before desktop computers, how did astronomers handle calculations of dates and times accurately, for example two plates taken decades apart, how would an astronomer calculate the time difference precisely?
history time terminology
edited yesterday
Glorfindel
1,9612924
asked yesterday
Ubiquitous StudentUbiquitous Student
19316
New contributor
Ubiquitous Student is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
|
show 3 more comments
$begingroup$
It always was interesting for me to understand the answer for the question:
What's the reason that we have a different number of days each month?
If the month is fixed on the time that the moon circles the earth, then the time of the circling isn't equal each month? And if the month fixed by the time that the earth circles the sun and then divided by 12 (365:12=30.4), why one month has more days and the other month has less days?
Before desktop computers, how did astronomers handle calculations of dates and times accurately, for example two plates taken decades apart, how would an astronomer calculate the time difference precisely?
history time terminology
edited yesterday
Glorfindel
1,9612924
asked yesterday
Ubiquitous StudentUbiquitous Student
19316
New contributor
Ubiquitous Student is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
1
$begingroup$
I've added an extra sentence to keep your question on-topic in Astronomy and not just about the history of calendars and how the month is defined for modern Gregorian calendars.
$endgroup$
– uhoh
yesterday
$begingroup$
only slightly related, calendar history/trivia in VSauce's How Earth Moves
$endgroup$
– uhoh
yesterday
2
$begingroup$
Since the Earth orbits the sun faster in January than it does in July (about 3.4% faster on Perihelion than Aphelion), then a case could be made for the months not being equal. In fact, Nov-April has 181 days (182 on leap years) and May-Oct has 184 days, which corresponds pretty well to how far the earth moves in each 6 month period. I don't know the historical reason for why it worked out that way.
$endgroup$
– userLTK
yesterday
$begingroup$
@userLTK wouldn't that be interesting if it turned out not to be a coincidence?
$endgroup$
– uhoh
yesterday
1
$begingroup$
@userLTK 'winter months are shorter than summer months on average' Hi from the other hemisphere :-)
$endgroup$
– mcalex
11 hours ago
|
show 3 more comments
$begingroup$
It always was interesting for me to understand the answer for the question:
What's the reason that we have a different number of days each month?
If the month is fixed on the time that the moon circles the earth, then the time of the circling isn't equal each month? And if the month fixed by the time that the earth circles the sun and then divided by 12 (365:12=30.4), why one month has more days and the other month has less days?
Before desktop computers, how did astronomers handle calculations of dates and times accurately, for example two plates taken decades apart, how would an astronomer calculate the time difference precisely?
history time terminology
edited yesterday
Glorfindel
1,9612924
asked yesterday
Ubiquitous StudentUbiquitous Student
19316
New contributor
Ubiquitous Student is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
It always was interesting for me to understand the answer for the question:
What's the reason that we have a different number of days each month?
If the month is fixed on the time that the moon circles the earth, then the time of the circling isn't equal each month? And if the month fixed by the time that the earth circles the sun and then divided by 12 (365:12=30.4), why one month has more days and the other month has less days?
Before desktop computers, how did astronomers handle calculations of dates and times accurately, for example two plates taken decades apart, how would an astronomer calculate the time difference precisely?
history time terminology
history time terminology
edited yesterday
Glorfindel
1,9612924
asked yesterday
Ubiquitous StudentUbiquitous Student
19316
New contributor
Ubiquitous Student is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
edited yesterday
Glorfindel
1,9612924
asked yesterday
Ubiquitous StudentUbiquitous Student
19316
New contributor
Ubiquitous Student is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
edited yesterday
Glorfindel
1,9612924
edited yesterday
Glorfindel
1,9612924
edited yesterday
Glorfindel
1,9612924
1,9612924
asked yesterday
Ubiquitous StudentUbiquitous Student
19316
New contributor
Ubiquitous Student is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked yesterday
Ubiquitous StudentUbiquitous Student
19316
asked yesterday
Ubiquitous StudentUbiquitous Student
19316
19316
New contributor
Ubiquitous Student is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
New contributor
Ubiquitous Student is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
Ubiquitous Student is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
1
$begingroup$
I've added an extra sentence to keep your question on-topic in Astronomy and not just about the history of calendars and how the month is defined for modern Gregorian calendars.
$endgroup$
– uhoh
yesterday
$begingroup$
only slightly related, calendar history/trivia in VSauce's How Earth Moves
$endgroup$
– uhoh
yesterday
2
$begingroup$
Since the Earth orbits the sun faster in January than it does in July (about 3.4% faster on Perihelion than Aphelion), then a case could be made for the months not being equal. In fact, Nov-April has 181 days (182 on leap years) and May-Oct has 184 days, which corresponds pretty well to how far the earth moves in each 6 month period. I don't know the historical reason for why it worked out that way.
$endgroup$
– userLTK
yesterday
$begingroup$
@userLTK wouldn't that be interesting if it turned out not to be a coincidence?
$endgroup$
– uhoh
yesterday
1
$begingroup$
@userLTK 'winter months are shorter than summer months on average' Hi from the other hemisphere :-)
$endgroup$
– mcalex
11 hours ago
|
show 3 more comments
1
$begingroup$
I've added an extra sentence to keep your question on-topic in Astronomy and not just about the history of calendars and how the month is defined for modern Gregorian calendars.
$endgroup$
– uhoh
yesterday
$begingroup$
only slightly related, calendar history/trivia in VSauce's How Earth Moves
$endgroup$
– uhoh
yesterday
2
$begingroup$
Since the Earth orbits the sun faster in January than it does in July (about 3.4% faster on Perihelion than Aphelion), then a case could be made for the months not being equal. In fact, Nov-April has 181 days (182 on leap years) and May-Oct has 184 days, which corresponds pretty well to how far the earth moves in each 6 month period. I don't know the historical reason for why it worked out that way.
$endgroup$
– userLTK
yesterday
$begingroup$
@userLTK wouldn't that be interesting if it turned out not to be a coincidence?
$endgroup$
– uhoh
yesterday
1
$begingroup$
@userLTK 'winter months are shorter than summer months on average' Hi from the other hemisphere :-)
$endgroup$
– mcalex
11 hours ago
1
1
$begingroup$
I've added an extra sentence to keep your question on-topic in Astronomy and not just about the history of calendars and how the month is defined for modern Gregorian calendars.
$endgroup$
– uhoh
yesterday
$begingroup$
I've added an extra sentence to keep your question on-topic in Astronomy and not just about the history of calendars and how the month is defined for modern Gregorian calendars.
$endgroup$
– uhoh
yesterday
$begingroup$
only slightly related, calendar history/trivia in VSauce's How Earth Moves
$endgroup$
– uhoh
yesterday
$begingroup$
only slightly related, calendar history/trivia in VSauce's How Earth Moves
$endgroup$
– uhoh
yesterday
2
2
$begingroup$
Since the Earth orbits the sun faster in January than it does in July (about 3.4% faster on Perihelion than Aphelion), then a case could be made for the months not being equal. In fact, Nov-April has 181 days (182 on leap years) and May-Oct has 184 days, which corresponds pretty well to how far the earth moves in each 6 month period. I don't know the historical reason for why it worked out that way.
$endgroup$
– userLTK
yesterday
$begingroup$
Since the Earth orbits the sun faster in January than it does in July (about 3.4% faster on Perihelion than Aphelion), then a case could be made for the months not being equal. In fact, Nov-April has 181 days (182 on leap years) and May-Oct has 184 days, which corresponds pretty well to how far the earth moves in each 6 month period. I don't know the historical reason for why it worked out that way.
$endgroup$
– userLTK
yesterday
$begingroup$
@userLTK wouldn't that be interesting if it turned out not to be a coincidence?
$endgroup$
– uhoh
yesterday
$begingroup$
@userLTK wouldn't that be interesting if it turned out not to be a coincidence?
$endgroup$
– uhoh
yesterday
1
1
$begingroup$
@userLTK 'winter months are shorter than summer months on average' Hi from the other hemisphere :-)
$endgroup$
– mcalex
11 hours ago
$begingroup$
@userLTK 'winter months are shorter than summer months on average' Hi from the other hemisphere :-)
$endgroup$
– mcalex
11 hours ago
|
show 3 more comments
1 Answer
1
active
oldest
votes
$begingroup$
You make a great point. The reason behind the discrepancy between the dates is due to a complicated history behind it.
The calendar is based on the calendar created by ancient Romans, which is based on one Moon cycle. One lunar cycle is
29.53 days.
www.universetoday.com/20620/lunar-year/
which does not evenly divide into the 365.25 days of the year.
Note: The Romans borrowed the calendar from the ancient Greeks to develop the idea of a 10-month calendar that left approximately 60 days unaccounted for.
Consequently, the earliest ancient Roman calendars had months that were either 29 or 30 days to account for this discrepancy.
The Romans started using the 10-month calendar in 738 B.C. that included Martius[March], Aprilis[April], Maius[May], Junius[June], Quintilis[July, quin- meaning "5"], Sextilis[August, sex- meaning "6"], September["7"], October["8"], November["9"], and December["10"].
To account for the remaining $pm60$ days, Januarius[January] was added to the beginning of the year and Februarius[February] to the end of the year during Numa's reign around 700 B.C. with a leap year every 4 years.
Leap years were decreed by proclamation the pontifex maximus, in such years an extra month was added to the calendar.
Quoted from PM 2Ring
The calendar stayed in that order until 452 B.C. when a small council of Romans, called the Decemvirs, moved February to follow January.
However,
in the initial 36 years of its adoption leap days were added every 3 years due to a misunderstanding (Romans used inclusive counting),
Quoted from PM 2Ring
so that caused a big problem. In fact, by the start of the reign of Julius Caesar, the previous calendar was off by a whole week!
Julius Caesar noticed this and thus modified the Roman calendar in 46 B.C. to make each month have either 30 or 31 days, with the exception of Februarius[February], which had 29 days, with the three year leap year fixed into a four year leap year. Quintilis[July] was later renamed Julius[July] in his honor. Likewise, Sextilis[August] later became Augustus[August] to honor Augustus (Gaius Octavius, the first Roman Emperor). Augustus[August] was also given an extra day (taken away from Februarius[February]), so that Augustus and Julius would have an equal number of days, representing their equal power. This is the Julian Calendar.
This calendar was extremely accurate, but was still not accurate
enough as it drifts by approximately 3 days every 400 years. So after
a few hundred years, the drift becomes noticeable
(i.e. the seasons don't properly match the calendar), which is
important for farming, and therefore human survival.
quoted from CJ Dennis
Then a pope named Pope Gregory XIII modified the Julian calendar again in October 1582. This is the currently used Gregorian calendar. He made it so that
Every year that is exactly divisible by four is a leap year, except for years that are exactly divisible by 100, but these centurial years are leap years if they are exactly divisible by 400.
https://en.wikipedia.org/wiki/Gregorian_calendar
This calendar is the most accurate calendar currently used, and won't be a single day off until the year of $pm 3200$ AD. It isn't perfect though. Compared to the tropical year, it is 27 seconds too long. This is...
due to astronomical effects (the
rotation of the Earth speeding up and slowing down, etc.) we can't be
more precise than that.
quoted from CJ Dennis
As for your other question, unless the plates taken had accurate dates of when recorded, it would be rather impossible to calculate precisely.
answered yesterday
Max0815Max0815
593216
New contributor
Max0815 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
1
$begingroup$
There are some errors in this answer. Eg, before the adoption of the Julian calendar, leap years were decreed by proclamation the pontifex maximus, in such years an extra month was added to the calendar. In the Julian calendar, there is a leap day every 4 years (with no exception for century years), but in the initial 36 years of its adoption leap days were added every 3 years due to a misunderstanding (Romans used inclusive counting). See en.m.wikipedia.org/wiki/Julian_calendar#Leap_year_error
$endgroup$
– PM 2Ring
yesterday
1
$begingroup$
@CJDennis its 3200 years for 1 day to be off. I checked in my notes from science class.
$endgroup$
– Max0815
yesterday
8
$begingroup$
This calendar is the most accurate calendar there is. Not so. It's the most accurate calendar in popular usage. Other ancient calendars were slightly more accurate than ours (by seconds in centuries). Our current one is accurate enough.
$endgroup$
– CJ Dennis
yesterday
2
$begingroup$
@CJDennis Not just ancient calendars. The Revised Julian Calendar used by some Orthodox churches is more accurate than the Gregorian calendar (and is identical to the Gregorian calendar until the year 2800). en.wikipedia.org/wiki/Revised_Julian_calendar
$endgroup$
– Mike Scott
yesterday
2
$begingroup$
An interesting aside, to effect the switch to Gregorian calendar a papal bull was used that specified a precise algorithm to compute the calendar dates, leap years, and adjust the dates from julian precisely. These efforts were done to have the most accurate estimate of easter, but now define the Gregorian calendar. This canon law is an early example of a law based on an algorithm.
$endgroup$
– crasic
20 hours ago
|
show 5 more comments
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1 Answer
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1 Answer
1
active
oldest
votes
active
oldest
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active
oldest
votes
$begingroup$
You make a great point. The reason behind the discrepancy between the dates is due to a complicated history behind it.
The calendar is based on the calendar created by ancient Romans, which is based on one Moon cycle. One lunar cycle is
29.53 days.
www.universetoday.com/20620/lunar-year/
which does not evenly divide into the 365.25 days of the year.
Note: The Romans borrowed the calendar from the ancient Greeks to develop the idea of a 10-month calendar that left approximately 60 days unaccounted for.
Consequently, the earliest ancient Roman calendars had months that were either 29 or 30 days to account for this discrepancy.
The Romans started using the 10-month calendar in 738 B.C. that included Martius[March], Aprilis[April], Maius[May], Junius[June], Quintilis[July, quin- meaning "5"], Sextilis[August, sex- meaning "6"], September["7"], October["8"], November["9"], and December["10"].
To account for the remaining $pm60$ days, Januarius[January] was added to the beginning of the year and Februarius[February] to the end of the year during Numa's reign around 700 B.C. with a leap year every 4 years.
Leap years were decreed by proclamation the pontifex maximus, in such years an extra month was added to the calendar.
Quoted from PM 2Ring
The calendar stayed in that order until 452 B.C. when a small council of Romans, called the Decemvirs, moved February to follow January.
However,
in the initial 36 years of its adoption leap days were added every 3 years due to a misunderstanding (Romans used inclusive counting),
Quoted from PM 2Ring
so that caused a big problem. In fact, by the start of the reign of Julius Caesar, the previous calendar was off by a whole week!
Julius Caesar noticed this and thus modified the Roman calendar in 46 B.C. to make each month have either 30 or 31 days, with the exception of Februarius[February], which had 29 days, with the three year leap year fixed into a four year leap year. Quintilis[July] was later renamed Julius[July] in his honor. Likewise, Sextilis[August] later became Augustus[August] to honor Augustus (Gaius Octavius, the first Roman Emperor). Augustus[August] was also given an extra day (taken away from Februarius[February]), so that Augustus and Julius would have an equal number of days, representing their equal power. This is the Julian Calendar.
This calendar was extremely accurate, but was still not accurate
enough as it drifts by approximately 3 days every 400 years. So after
a few hundred years, the drift becomes noticeable
(i.e. the seasons don't properly match the calendar), which is
important for farming, and therefore human survival.
quoted from CJ Dennis
Then a pope named Pope Gregory XIII modified the Julian calendar again in October 1582. This is the currently used Gregorian calendar. He made it so that
Every year that is exactly divisible by four is a leap year, except for years that are exactly divisible by 100, but these centurial years are leap years if they are exactly divisible by 400.
https://en.wikipedia.org/wiki/Gregorian_calendar
This calendar is the most accurate calendar currently used, and won't be a single day off until the year of $pm 3200$ AD. It isn't perfect though. Compared to the tropical year, it is 27 seconds too long. This is...
due to astronomical effects (the
rotation of the Earth speeding up and slowing down, etc.) we can't be
more precise than that.
quoted from CJ Dennis
As for your other question, unless the plates taken had accurate dates of when recorded, it would be rather impossible to calculate precisely.
answered yesterday
Max0815Max0815
593216
New contributor
Max0815 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
1
$begingroup$
There are some errors in this answer. Eg, before the adoption of the Julian calendar, leap years were decreed by proclamation the pontifex maximus, in such years an extra month was added to the calendar. In the Julian calendar, there is a leap day every 4 years (with no exception for century years), but in the initial 36 years of its adoption leap days were added every 3 years due to a misunderstanding (Romans used inclusive counting). See en.m.wikipedia.org/wiki/Julian_calendar#Leap_year_error
$endgroup$
– PM 2Ring
yesterday
1
$begingroup$
@CJDennis its 3200 years for 1 day to be off. I checked in my notes from science class.
$endgroup$
– Max0815
yesterday
8
$begingroup$
This calendar is the most accurate calendar there is. Not so. It's the most accurate calendar in popular usage. Other ancient calendars were slightly more accurate than ours (by seconds in centuries). Our current one is accurate enough.
$endgroup$
– CJ Dennis
yesterday
2
$begingroup$
@CJDennis Not just ancient calendars. The Revised Julian Calendar used by some Orthodox churches is more accurate than the Gregorian calendar (and is identical to the Gregorian calendar until the year 2800). en.wikipedia.org/wiki/Revised_Julian_calendar
$endgroup$
– Mike Scott
yesterday
2
$begingroup$
An interesting aside, to effect the switch to Gregorian calendar a papal bull was used that specified a precise algorithm to compute the calendar dates, leap years, and adjust the dates from julian precisely. These efforts were done to have the most accurate estimate of easter, but now define the Gregorian calendar. This canon law is an early example of a law based on an algorithm.
$endgroup$
– crasic
20 hours ago
|
show 5 more comments
$begingroup$
You make a great point. The reason behind the discrepancy between the dates is due to a complicated history behind it.
The calendar is based on the calendar created by ancient Romans, which is based on one Moon cycle. One lunar cycle is
29.53 days.
www.universetoday.com/20620/lunar-year/
which does not evenly divide into the 365.25 days of the year.
Note: The Romans borrowed the calendar from the ancient Greeks to develop the idea of a 10-month calendar that left approximately 60 days unaccounted for.
Consequently, the earliest ancient Roman calendars had months that were either 29 or 30 days to account for this discrepancy.
The Romans started using the 10-month calendar in 738 B.C. that included Martius[March], Aprilis[April], Maius[May], Junius[June], Quintilis[July, quin- meaning "5"], Sextilis[August, sex- meaning "6"], September["7"], October["8"], November["9"], and December["10"].
To account for the remaining $pm60$ days, Januarius[January] was added to the beginning of the year and Februarius[February] to the end of the year during Numa's reign around 700 B.C. with a leap year every 4 years.
Leap years were decreed by proclamation the pontifex maximus, in such years an extra month was added to the calendar.
Quoted from PM 2Ring
The calendar stayed in that order until 452 B.C. when a small council of Romans, called the Decemvirs, moved February to follow January.
However,
in the initial 36 years of its adoption leap days were added every 3 years due to a misunderstanding (Romans used inclusive counting),
Quoted from PM 2Ring
so that caused a big problem. In fact, by the start of the reign of Julius Caesar, the previous calendar was off by a whole week!
Julius Caesar noticed this and thus modified the Roman calendar in 46 B.C. to make each month have either 30 or 31 days, with the exception of Februarius[February], which had 29 days, with the three year leap year fixed into a four year leap year. Quintilis[July] was later renamed Julius[July] in his honor. Likewise, Sextilis[August] later became Augustus[August] to honor Augustus (Gaius Octavius, the first Roman Emperor). Augustus[August] was also given an extra day (taken away from Februarius[February]), so that Augustus and Julius would have an equal number of days, representing their equal power. This is the Julian Calendar.
This calendar was extremely accurate, but was still not accurate
enough as it drifts by approximately 3 days every 400 years. So after
a few hundred years, the drift becomes noticeable
(i.e. the seasons don't properly match the calendar), which is
important for farming, and therefore human survival.
quoted from CJ Dennis
Then a pope named Pope Gregory XIII modified the Julian calendar again in October 1582. This is the currently used Gregorian calendar. He made it so that
Every year that is exactly divisible by four is a leap year, except for years that are exactly divisible by 100, but these centurial years are leap years if they are exactly divisible by 400.
https://en.wikipedia.org/wiki/Gregorian_calendar
This calendar is the most accurate calendar currently used, and won't be a single day off until the year of $pm 3200$ AD. It isn't perfect though. Compared to the tropical year, it is 27 seconds too long. This is...
due to astronomical effects (the
rotation of the Earth speeding up and slowing down, etc.) we can't be
more precise than that.
quoted from CJ Dennis
As for your other question, unless the plates taken had accurate dates of when recorded, it would be rather impossible to calculate precisely.
answered yesterday
Max0815Max0815
593216
New contributor
Max0815 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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1
$begingroup$
There are some errors in this answer. Eg, before the adoption of the Julian calendar, leap years were decreed by proclamation the pontifex maximus, in such years an extra month was added to the calendar. In the Julian calendar, there is a leap day every 4 years (with no exception for century years), but in the initial 36 years of its adoption leap days were added every 3 years due to a misunderstanding (Romans used inclusive counting). See en.m.wikipedia.org/wiki/Julian_calendar#Leap_year_error
$endgroup$
– PM 2Ring
yesterday
1
$begingroup$
@CJDennis its 3200 years for 1 day to be off. I checked in my notes from science class.
$endgroup$
– Max0815
yesterday
8
$begingroup$
This calendar is the most accurate calendar there is. Not so. It's the most accurate calendar in popular usage. Other ancient calendars were slightly more accurate than ours (by seconds in centuries). Our current one is accurate enough.
$endgroup$
– CJ Dennis
yesterday
2
$begingroup$
@CJDennis Not just ancient calendars. The Revised Julian Calendar used by some Orthodox churches is more accurate than the Gregorian calendar (and is identical to the Gregorian calendar until the year 2800). en.wikipedia.org/wiki/Revised_Julian_calendar
$endgroup$
– Mike Scott
yesterday
2
$begingroup$
An interesting aside, to effect the switch to Gregorian calendar a papal bull was used that specified a precise algorithm to compute the calendar dates, leap years, and adjust the dates from julian precisely. These efforts were done to have the most accurate estimate of easter, but now define the Gregorian calendar. This canon law is an early example of a law based on an algorithm.
$endgroup$
– crasic
20 hours ago
|
show 5 more comments
$begingroup$
You make a great point. The reason behind the discrepancy between the dates is due to a complicated history behind it.
The calendar is based on the calendar created by ancient Romans, which is based on one Moon cycle. One lunar cycle is
29.53 days.
www.universetoday.com/20620/lunar-year/
which does not evenly divide into the 365.25 days of the year.
Note: The Romans borrowed the calendar from the ancient Greeks to develop the idea of a 10-month calendar that left approximately 60 days unaccounted for.
Consequently, the earliest ancient Roman calendars had months that were either 29 or 30 days to account for this discrepancy.
The Romans started using the 10-month calendar in 738 B.C. that included Martius[March], Aprilis[April], Maius[May], Junius[June], Quintilis[July, quin- meaning "5"], Sextilis[August, sex- meaning "6"], September["7"], October["8"], November["9"], and December["10"].
To account for the remaining $pm60$ days, Januarius[January] was added to the beginning of the year and Februarius[February] to the end of the year during Numa's reign around 700 B.C. with a leap year every 4 years.
Leap years were decreed by proclamation the pontifex maximus, in such years an extra month was added to the calendar.
Quoted from PM 2Ring
The calendar stayed in that order until 452 B.C. when a small council of Romans, called the Decemvirs, moved February to follow January.
However,
in the initial 36 years of its adoption leap days were added every 3 years due to a misunderstanding (Romans used inclusive counting),
Quoted from PM 2Ring
so that caused a big problem. In fact, by the start of the reign of Julius Caesar, the previous calendar was off by a whole week!
Julius Caesar noticed this and thus modified the Roman calendar in 46 B.C. to make each month have either 30 or 31 days, with the exception of Februarius[February], which had 29 days, with the three year leap year fixed into a four year leap year. Quintilis[July] was later renamed Julius[July] in his honor. Likewise, Sextilis[August] later became Augustus[August] to honor Augustus (Gaius Octavius, the first Roman Emperor). Augustus[August] was also given an extra day (taken away from Februarius[February]), so that Augustus and Julius would have an equal number of days, representing their equal power. This is the Julian Calendar.
This calendar was extremely accurate, but was still not accurate
enough as it drifts by approximately 3 days every 400 years. So after
a few hundred years, the drift becomes noticeable
(i.e. the seasons don't properly match the calendar), which is
important for farming, and therefore human survival.
quoted from CJ Dennis
Then a pope named Pope Gregory XIII modified the Julian calendar again in October 1582. This is the currently used Gregorian calendar. He made it so that
Every year that is exactly divisible by four is a leap year, except for years that are exactly divisible by 100, but these centurial years are leap years if they are exactly divisible by 400.
https://en.wikipedia.org/wiki/Gregorian_calendar
This calendar is the most accurate calendar currently used, and won't be a single day off until the year of $pm 3200$ AD. It isn't perfect though. Compared to the tropical year, it is 27 seconds too long. This is...
due to astronomical effects (the
rotation of the Earth speeding up and slowing down, etc.) we can't be
more precise than that.
quoted from CJ Dennis
As for your other question, unless the plates taken had accurate dates of when recorded, it would be rather impossible to calculate precisely.
answered yesterday
Max0815Max0815
593216
New contributor
Max0815 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
You make a great point. The reason behind the discrepancy between the dates is due to a complicated history behind it.
The calendar is based on the calendar created by ancient Romans, which is based on one Moon cycle. One lunar cycle is
29.53 days.
www.universetoday.com/20620/lunar-year/
which does not evenly divide into the 365.25 days of the year.
Note: The Romans borrowed the calendar from the ancient Greeks to develop the idea of a 10-month calendar that left approximately 60 days unaccounted for.
Consequently, the earliest ancient Roman calendars had months that were either 29 or 30 days to account for this discrepancy.
The Romans started using the 10-month calendar in 738 B.C. that included Martius[March], Aprilis[April], Maius[May], Junius[June], Quintilis[July, quin- meaning "5"], Sextilis[August, sex- meaning "6"], September["7"], October["8"], November["9"], and December["10"].
To account for the remaining $pm60$ days, Januarius[January] was added to the beginning of the year and Februarius[February] to the end of the year during Numa's reign around 700 B.C. with a leap year every 4 years.
Leap years were decreed by proclamation the pontifex maximus, in such years an extra month was added to the calendar.
Quoted from PM 2Ring
The calendar stayed in that order until 452 B.C. when a small council of Romans, called the Decemvirs, moved February to follow January.
However,
in the initial 36 years of its adoption leap days were added every 3 years due to a misunderstanding (Romans used inclusive counting),
Quoted from PM 2Ring
so that caused a big problem. In fact, by the start of the reign of Julius Caesar, the previous calendar was off by a whole week!
Julius Caesar noticed this and thus modified the Roman calendar in 46 B.C. to make each month have either 30 or 31 days, with the exception of Februarius[February], which had 29 days, with the three year leap year fixed into a four year leap year. Quintilis[July] was later renamed Julius[July] in his honor. Likewise, Sextilis[August] later became Augustus[August] to honor Augustus (Gaius Octavius, the first Roman Emperor). Augustus[August] was also given an extra day (taken away from Februarius[February]), so that Augustus and Julius would have an equal number of days, representing their equal power. This is the Julian Calendar.
This calendar was extremely accurate, but was still not accurate
enough as it drifts by approximately 3 days every 400 years. So after
a few hundred years, the drift becomes noticeable
(i.e. the seasons don't properly match the calendar), which is
important for farming, and therefore human survival.
quoted from CJ Dennis
Then a pope named Pope Gregory XIII modified the Julian calendar again in October 1582. This is the currently used Gregorian calendar. He made it so that
Every year that is exactly divisible by four is a leap year, except for years that are exactly divisible by 100, but these centurial years are leap years if they are exactly divisible by 400.
https://en.wikipedia.org/wiki/Gregorian_calendar
This calendar is the most accurate calendar currently used, and won't be a single day off until the year of $pm 3200$ AD. It isn't perfect though. Compared to the tropical year, it is 27 seconds too long. This is...
due to astronomical effects (the
rotation of the Earth speeding up and slowing down, etc.) we can't be
more precise than that.
quoted from CJ Dennis
As for your other question, unless the plates taken had accurate dates of when recorded, it would be rather impossible to calculate precisely.
answered yesterday
Max0815Max0815
593216
New contributor
Max0815 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
edited 23 hours ago
answered yesterday
Max0815Max0815
593216
New contributor
Max0815 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
answered yesterday
Max0815Max0815
593216
answered yesterday
Max0815Max0815
593216
593216
New contributor
Max0815 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
New contributor
Max0815 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
Max0815 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
1
$begingroup$
There are some errors in this answer. Eg, before the adoption of the Julian calendar, leap years were decreed by proclamation the pontifex maximus, in such years an extra month was added to the calendar. In the Julian calendar, there is a leap day every 4 years (with no exception for century years), but in the initial 36 years of its adoption leap days were added every 3 years due to a misunderstanding (Romans used inclusive counting). See en.m.wikipedia.org/wiki/Julian_calendar#Leap_year_error
$endgroup$
– PM 2Ring
yesterday
1
$begingroup$
@CJDennis its 3200 years for 1 day to be off. I checked in my notes from science class.
$endgroup$
– Max0815
yesterday
8
$begingroup$
This calendar is the most accurate calendar there is. Not so. It's the most accurate calendar in popular usage. Other ancient calendars were slightly more accurate than ours (by seconds in centuries). Our current one is accurate enough.
$endgroup$
– CJ Dennis
yesterday
2
$begingroup$
@CJDennis Not just ancient calendars. The Revised Julian Calendar used by some Orthodox churches is more accurate than the Gregorian calendar (and is identical to the Gregorian calendar until the year 2800). en.wikipedia.org/wiki/Revised_Julian_calendar
$endgroup$
– Mike Scott
yesterday
2
$begingroup$
An interesting aside, to effect the switch to Gregorian calendar a papal bull was used that specified a precise algorithm to compute the calendar dates, leap years, and adjust the dates from julian precisely. These efforts were done to have the most accurate estimate of easter, but now define the Gregorian calendar. This canon law is an early example of a law based on an algorithm.
$endgroup$
– crasic
20 hours ago
|
show 5 more comments
1
$begingroup$
There are some errors in this answer. Eg, before the adoption of the Julian calendar, leap years were decreed by proclamation the pontifex maximus, in such years an extra month was added to the calendar. In the Julian calendar, there is a leap day every 4 years (with no exception for century years), but in the initial 36 years of its adoption leap days were added every 3 years due to a misunderstanding (Romans used inclusive counting). See en.m.wikipedia.org/wiki/Julian_calendar#Leap_year_error
$endgroup$
– PM 2Ring
yesterday
1
$begingroup$
@CJDennis its 3200 years for 1 day to be off. I checked in my notes from science class.
$endgroup$
– Max0815
yesterday
8
$begingroup$
This calendar is the most accurate calendar there is. Not so. It's the most accurate calendar in popular usage. Other ancient calendars were slightly more accurate than ours (by seconds in centuries). Our current one is accurate enough.
$endgroup$
– CJ Dennis
yesterday
2
$begingroup$
@CJDennis Not just ancient calendars. The Revised Julian Calendar used by some Orthodox churches is more accurate than the Gregorian calendar (and is identical to the Gregorian calendar until the year 2800). en.wikipedia.org/wiki/Revised_Julian_calendar
$endgroup$
– Mike Scott
yesterday
2
$begingroup$
An interesting aside, to effect the switch to Gregorian calendar a papal bull was used that specified a precise algorithm to compute the calendar dates, leap years, and adjust the dates from julian precisely. These efforts were done to have the most accurate estimate of easter, but now define the Gregorian calendar. This canon law is an early example of a law based on an algorithm.
$endgroup$
– crasic
20 hours ago
1
1
$begingroup$
There are some errors in this answer. Eg, before the adoption of the Julian calendar, leap years were decreed by proclamation the pontifex maximus, in such years an extra month was added to the calendar. In the Julian calendar, there is a leap day every 4 years (with no exception for century years), but in the initial 36 years of its adoption leap days were added every 3 years due to a misunderstanding (Romans used inclusive counting). See en.m.wikipedia.org/wiki/Julian_calendar#Leap_year_error
$endgroup$
– PM 2Ring
yesterday
$begingroup$
There are some errors in this answer. Eg, before the adoption of the Julian calendar, leap years were decreed by proclamation the pontifex maximus, in such years an extra month was added to the calendar. In the Julian calendar, there is a leap day every 4 years (with no exception for century years), but in the initial 36 years of its adoption leap days were added every 3 years due to a misunderstanding (Romans used inclusive counting). See en.m.wikipedia.org/wiki/Julian_calendar#Leap_year_error
$endgroup$
– PM 2Ring
yesterday
1
1
$begingroup$
@CJDennis its 3200 years for 1 day to be off. I checked in my notes from science class.
$endgroup$
– Max0815
yesterday
$begingroup$
@CJDennis its 3200 years for 1 day to be off. I checked in my notes from science class.
$endgroup$
– Max0815
yesterday
8
8
$begingroup$
This calendar is the most accurate calendar there is. Not so. It's the most accurate calendar in popular usage. Other ancient calendars were slightly more accurate than ours (by seconds in centuries). Our current one is accurate enough.
$endgroup$
– CJ Dennis
yesterday
$begingroup$
This calendar is the most accurate calendar there is. Not so. It's the most accurate calendar in popular usage. Other ancient calendars were slightly more accurate than ours (by seconds in centuries). Our current one is accurate enough.
$endgroup$
– CJ Dennis
yesterday
2
2
$begingroup$
@CJDennis Not just ancient calendars. The Revised Julian Calendar used by some Orthodox churches is more accurate than the Gregorian calendar (and is identical to the Gregorian calendar until the year 2800). en.wikipedia.org/wiki/Revised_Julian_calendar
$endgroup$
– Mike Scott
yesterday
$begingroup$
@CJDennis Not just ancient calendars. The Revised Julian Calendar used by some Orthodox churches is more accurate than the Gregorian calendar (and is identical to the Gregorian calendar until the year 2800). en.wikipedia.org/wiki/Revised_Julian_calendar
$endgroup$
– Mike Scott
yesterday
2
2
$begingroup$
An interesting aside, to effect the switch to Gregorian calendar a papal bull was used that specified a precise algorithm to compute the calendar dates, leap years, and adjust the dates from julian precisely. These efforts were done to have the most accurate estimate of easter, but now define the Gregorian calendar. This canon law is an early example of a law based on an algorithm.
$endgroup$
– crasic
20 hours ago
$begingroup$
An interesting aside, to effect the switch to Gregorian calendar a papal bull was used that specified a precise algorithm to compute the calendar dates, leap years, and adjust the dates from julian precisely. These efforts were done to have the most accurate estimate of easter, but now define the Gregorian calendar. This canon law is an early example of a law based on an algorithm.
$endgroup$
– crasic
20 hours ago
|
show 5 more comments
Ubiquitous Student is a new contributor. Be nice, and check out our Code of Conduct.
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1
$begingroup$
I've added an extra sentence to keep your question on-topic in Astronomy and not just about the history of calendars and how the month is defined for modern Gregorian calendars.
$endgroup$
– uhoh
yesterday
$begingroup$
only slightly related, calendar history/trivia in VSauce's How Earth Moves
$endgroup$
– uhoh
yesterday
2
$begingroup$
Since the Earth orbits the sun faster in January than it does in July (about 3.4% faster on Perihelion than Aphelion), then a case could be made for the months not being equal. In fact, Nov-April has 181 days (182 on leap years) and May-Oct has 184 days, which corresponds pretty well to how far the earth moves in each 6 month period. I don't know the historical reason for why it worked out that way.
$endgroup$
– userLTK
yesterday
$begingroup$
@userLTK wouldn't that be interesting if it turned out not to be a coincidence?
$endgroup$
– uhoh
yesterday
1
$begingroup$
@userLTK 'winter months are shorter than summer months on average' Hi from the other hemisphere :-)
$endgroup$
– mcalex
11 hours ago