<p>The Gregorian calendar is designed to approximate the average tropical year, that is the average length of time from one spring equinox to the next.</p>
<p>The actual average length of a tropical year is 365.2422 days.  The average length of a Gregorian year is 365.2425 days</p>
<p>So although it isn't perfect, it would take many thousands of years for the discrepancy to become noticeable. From year to year, the date of the spring equinox will move a little, it will always stay close to March 21st. (for generations to come) This is not a huge error; it is a tiny error that you will never notice in your life time.</p>
<p>It would be possible to design a calendar that started the year exactly on the spring equinox, (or winter solstice, for example)  But then the clocks would not be aligned to the day time, which would be very inconvenient.</p>

CC BY-SA 4.0
2023-09-16T09:33:32.707Z
FWIW, the March equinox tropical year is (currently) slightly longer than the mean tropical year. See https://en.wikipedia.org/wiki/Tropical_year#Different_tropical_year_definitions
PM 2Ring
CC BY-SA 4.0
2023-09-19T00:09:32.797Z
For any calendar reformers here, the shortest-cycle approximation accurate to 7 significant digits is 31 leap years every 128 years, giving an average of 365.2421875 days per year.
dan04
CC BY-SA 4.0
2023-10-27T23:44:18.717Z
You mean 11111₂ leap years every 10000000₂ years  (clearly the solar system is a simulation)
James K
CC BY-SA 4.0
2023-09-15T21:05:45.107Z
2023-09-15T21:05:45.107Z
James K
<p>While Gregorian calendar is a solar year it always start on 00:00 each year. But for sure the Earth completes each orbit around the Sun on different times each year.</p>
<p>So if we put January 1 as the start of the year we should calculate the exact time when the Earth completes its orbit around the Sun the Jan 1 of the next year.</p>
<p>So why does Gregorian calendar insists on celebrating each year on 00:00? Doesn't it cause a huge error in the future?</p>

CC BY-SA 4.0
2023-09-15T20:18:28.890Z
The Gregorian Calendar year is based on a calculated mean year  The main concern was that the March 20th be the date that the March Equinox happens on,  year over year., and a reasonable, human-computable formula for the number of days in each year. It was more important that the length of years be regular and predictable, than a specific astronomical event be used to pin the start of the year.
notovny
<sidereal-period><synodic-period><period>
Doesn't Gregorian Calendar being started each year on 00:00 cause a huge error in the future?
Snack Exchange
# Doesn't Gregorian Calendar being started each year on 00:00 cause a huge error in the future?

(Asked by: username_0 on 2023-09-15)

While Gregorian calendar is a solar year it always start on 00:00 each year. But for sure the Earth completes each orbit around the Sun on different times each year.

So if we put January 1 as the start of the year we should calculate the exact time when the Earth completes its orbit around the Sun the Jan 1 of the next year.

So why does Gregorian calendar insists on celebrating each year on 00:00? Doesn't it cause a huge error in the future?

**Tags:** sidereal-period, synodic-period, period

> **Comments:**
> **username_1**: The Gregorian Calendar year is based on a calculated mean year  The main concern was that the March 20th be the date that the March Equinox happens on,  year over year., and a reasonable, human-computable formula for the number of days in each year. It was more important that the length of years be regular and predictable, than a specific astronomical event be used to pin the start of the year.  

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## 1 answers

### Answer by username_2 on 2023-09-15. Score: 6 | Accepted answer

The Gregorian calendar is designed to approximate the average tropical year, that is the average length of time from one spring equinox to the next.

The actual average length of a tropical year is 365.2422 days. The average length of a Gregorian year is 365.2425 days

So although it isn't perfect, it would take many thousands of years for the discrepancy to become noticeable. From year to year, the date of the spring equinox will move a little, it will always stay close to March 21st. (for generations to come) This is not a huge error; it is a tiny error that you will never notice in your life time.

It would be possible to design a calendar that started the year exactly on the spring equinox, (or winter solstice, for example) But then the clocks would not be aligned to the day time, which would be very inconvenient.

> **Comments:**
> **username_3**: FWIW, the March equinox tropical year is (currently) slightly longer than the mean tropical year. See https://en.wikipedia.org/wiki/Tropical_year#Different_tropical_year_definitions  
> **username_4**: For any calendar reformers here, the shortest-cycle approximation accurate to 7 significant digits is 31 leap years every 128 years, giving an average of 365.2421875 days per year.  
> **username_2**: You mean 11111₂ leap years every 10000000₂ years  (clearly the solar system is a simulation)  

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