How many days are there in one year? The average person will say 365 days, NASA said it's 365.26 days long, the National Institute of Standards Technology said it's 365.242196, and some physicists say it's 365.26. These are all facts given by scientists but it seems that they couldn't agree what the exact time is. In order to find out what is the most precise number of days in a year, we need to look at the four principal years that are in use today.
The Julian year was introduced by Julius Caesar in 46 B.C with 365.25 days. However, it is not very precise because there was a counting error that occurred when during its first early use making the third year a leap year. This is also the reason why some holidays and fixed dates are not in sync with each other.
However, Julius Caesar ordered that it it will be the standard calendar at that time because the priests abused the calculations to manipulate the politics in Rome.
This time measurement is based on the number of days it takes Earth to reach the closest point to the sun, which is 365.259636 days. However, there is a problem with the anomalistic year because the Earth's orbit is different every year. Thanks to Jupiter which makes the ellipse where the Earth revolves around is imperfect. Therefore, if calculations are based on this point, you will get a wrong calculation as well.
The tropical year is based on the span of time from spring equinox to another spring equinox, which is approximately 365.2422 days. This is also the most common measure of year used by people. However, just like the anomalistic year, the tropical year has a problem - the Earth wobbles like a spinning top making the equator shift slightly which, in turn, changes the equinox as well.
The sidereal real is around 365.26 days long and based on the entire cosmos making it the most fixed frame you can use to measure time. It is also shorter by four minutes to the regular 24-hour time we use. However, this is what NASA and the astronomers use although it is imperfect as well.
Jonathan McDowell of the Harvard-Smithsonian Center for Astrophysics said that although the so-called fixed stars do not really stay permanently where they are, they just use it to point their telescopes to the same spot every day.
He also added that if you view time in light of the theory of relativity, it passes differently on Earth compared to other regions of the universe. Thus, no one really knows what the precise time is yet.
