The length of a year is based on how long it takes a planet to revolve around the Sun. Earth takes about 365.2422 days to make one revolution around the Sun,” Tavernier wrote. “That’s about six hours longer than the 365 days we typically include in a calendar year,” he added. As a result, to align our calendar with the Earth’s orbit, an extra day is added every four years at the end of February, known as Leap Day, accounting for the nearly 24 hours accumulated over that period.
Inquirer.net
Here’s my question: Why 365.2422 days in a year, and not 365 exactly?
With important things like the earth’s rotation around the sun, it should be exact. Right?
I suspect it has something to do with calculations and suppositions.
After all, early scientists no doubt correctly calculated the number of hours in a day, but would they have had the tools to be as precise as they needed to be? Could they have calculated to the 20th decimal place so the hours, days, months and years would work out on their calendars for hundreds or thousands of years?
And did they know about the “mean solar day” which is nearly 4 minutes longer than a “sidereal day”?
Consistency in nature
The earth spins one rotation every “day”, or 24 hours. It is so consistent, that it makes the news when it deviates by 1/500th of a second.
And, according to NASA, the earth’s standard “Sidereal orbit period” is 365.256 days, and its “Tropical orbit period” is 365.242 days.
[The Sidereal orbit period is the time that Earth takes to orbit the Sun once with respect to the fixed stars. The Tropical orbit period is the time it takes for the Sun, as seen from the Earth, to return to the same position along the ecliptic (its path among the stars)]
This is a difference of 0.014 days, or 0.336 hours, or 20.16 minutes…consistently…over years and years and years.
Similarly, as it travels, the earth’s orbital velocity maximums and minimums are 30.29 km/s and 29.29 km/s…a ONE KILOMETER PER SECOND DIFFERENCE.
Is it the calendars and holidays that cause the problems?
NASA gives excellent information about the development of calendar systems in history, as does, appropriately, Calendar.com.
The nature of the Sun brought with it enough calendar history to produce a Calendar. Very few things in this world can be depended on — but the sun is loyal, steady, and true. Its cycle is trustworthy year after year — making its emulation by all people through ages understandable.
“History of the Calendar”, Calendar.com
The Gregorian calendar is the most popular calendar used in the world today. But after studying its history, I started to wonder if all the changes made to it resulted in confusion and errors in attempting to align it with the Earth’s rotation around the Sun.
There are different calendars in different cultures… do they “fix” the “problem” ? Would we be better off with a calendar not based on a “year”, such as the “days elapsed” calendars like the Julian calendar?
The solar or lunisolar calendars requires a Leap Day correction. But what about a lunar-based calendar, such as the Jewish/Hebrew calendar?
The oldest calendar—still being used–is the Jewish/Hebrew calendar from c.3761 BC. I like the following quote from the comments section.
The Pesikta (Chapter 5) writes: “until the Exodus, G-d Himself calculated the months and years…once the Israelites left Egypt, He gave it to them.” In other words, prior to the Exodus, G-d declared the months and dates and told it to those who wished to know that information through Divine insight. I would note that only the forefathers, Abraham, Isaac, and Jacob, really used that information.
Chabad.org, Introduction to the Jewish Calendar
But all the calendars I found required some kind of correction (except the “days elapsed” calendars like the Julian calendar).
I think the significance of the leap year is that it’s a great reminder that the universe is really good at defying our attempts to devise nice and pretty and aesthetically pleasing systems to fit it in.
Jackie Faherty, astronomer at the American Museum of Natural History in New York, npr.org, February 26, 2024
Note to ponder
I’ll end my pondering on a positive note, with this simple, elegant thought from a writer at Teacher Bulletin:
“The leap year can serve as a reminder to evaluate how we are spending our time and whether we are using it in a way that aligns with God’s will for our lives. It is an opportunity to reflect on our priorities, make necessary adjustments, and seek God’s guidance in all that we do. So as we enter this leap year, let us make the most of this extra day and all the days that follow, using them to serve God and others, living a life that is pleasing to Him.”
Happily Writing 