How many days are in a year?

The orbital period in which the earth moves around the sun in its orbit is known as a year.

One Year


365 Days

The orbital period in which the earth moves around the sun in its orbit is known as a year. The number of days of the Earth’s orbital period is approximated in the calendar year. However, there are different types of a calendar that give a different approximation of the number of days in a year. These include the Gregorian calendar year, Julian year, Sidereal year and tropical year.

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Gregorian Year

According to the Gregorian calendar year, one common year has 365 days, while the leap year has 366 days. Leap years usually occur after every 4 years with an exception of the years that are not divisible by 400 but are divisible by 100. Therefore, the mean length of the Gregorian calendar can be expressed as;

1 mean year = 365 + ¼ - 1/100 + 1/400 = 365.2425 days

Julian Year

According to the definition, a Julian Year is used for astronomical calculations. However, it is not an actual measurement of an astrophysical phenomenon as it became revolutionary when it was introduced by Julius Caesar in 46 B.C. One Julian year is approximated to have 365.25 days, expressed as;

1 Julian year = 365.25 days.

Although the efficacy of the Julian calendar faded over the years, it is still used to define the light-year as a measurement of distance.

Sidereal Year

Most of the astronomers abide by the Sidereal calendar year since their solution is to measure time by the largest and most fixed frame they can find. This is the amount of time the sun takes to return to the same position relative to the most distant (fixed) stars. Thus a Sidereal year has 365 days, 6 hours, 9 minutes and 9 seconds. It can be expressed as;

1 Sidereal year = 365.25636 days

Tropical Year

The time the Earth takes to complete one cycle of the 4 seasons (spring, summer, autumn, and winter), is known as a Tropical calendar year. It is probably the most popular measure of a year that is widely used by people on earth. A tropical year has 365 days, 5 hours, 48 minutes and 46 seconds. It can also be expressed as;

1 Tropical year = 365.2422 days

A tropical year tells you when the seasons will change. However, there is a slight problem with its approximation since the earth wobbles. It means that there is a constant shift in the orientation of the Earth's equator but by a slight margin. You can check out the anomalistic year to determine how long that journey takes.