# The earth and the calendar

The earth is such a beautiful planet. It looks like a blue marble with white swirls. Some parts are brown, yellow, green and white.

The earth is such a beautiful planet. It looks like a blue marble with white swirls. Some parts are brown, yellow, green and white. The blue part is the water. Water covers most of Earth. The white swirls are clouds. The brown, yellow and green parts are land. And the white parts are ice and snow. In addition to this colourful display, answers to many of the intriguing questions can be obtained by studying the earth. For instance, we know that there are different seasons because the earth is tilted and the season depends on whether a place is tilted toward or away from the sun. We know the earth to be round and we know the movement of the earth brings about day and night. However, in this article, we will focus on the earth with the calendar.

We are getting to the end of the year and as you may have noticed, 2020 February had 29 days instead of the usual 28 days. This means that the total number of days in 2020 is 366 instead of the usual 365 days.

Do you remember the famous recital we were taught as we were growing up: 30 days has September, April, June and November, all the rest are 31 except February alone which has 28 days clear or 29 days in each leap year?

It has been acknowledged that for every leap year, an additional day is added. To make the case more sophisticated, Why is a leap day added to February and not the end of the year? Have you ever wondered why some months have more days than others, and also why February has the shortest days in the year? Why does February have 29 days only in a leap year?

As most of us already know, a day is measured as to how long it takes for the earth to rotate/spin on its axis which is equivalent to 24 hours. And we measure a year as to how long it takes for the earth to orbit or revolve around the sun which is also equivalent to 365 days on a calendar. But in reality, it takes 365.24219 days. It means we have an extra 0.24219 days which is roughly 0.25 days which is equivalent to a quarter of a day or 6 hours. So what do we do with this extra 6 hours? (6+6+6+6) 6 hours, four times will give us 24 hours which is equivalent to a day. We add them four times to obtain a day and create a leap phenomenon almost every 4 years. But how? To do that, we have to go back in time.

Once upon a time in the Roman Empire, lived an emperor called King Romulus. He was the first King of Rome, but he had a huge burden. This was because, he had difficulty in keeping tracks of seasons, festivals and numerous ceremonies. Therefore, he ordered to make a 10 months lunar calendar with each month consisting of 30/31, days that commenced in March(Martius) and ended with December. This calendar had a total of 304 days. Regardless, the calendar was not in sync with their 4 seasons(spring, summer, winter and autumn).

Later on, when King Numa Pompilus came into power, he decided to work on the problem by using a different approach. According to Romans, even numbers were a sign of bad luck and so to deal with this, he decided to remove a day from all the months that were even-numbered.

After these changes, the total number of days on their calendar became 298 days. But he was unhappy. He wanted the calendar to be in sync with the 12 phases of the moon.

The moon takes 29.5 days to turn into a new moon. ( A new moon occurs when the moon sits between the sun and the Earth. New moons occur during the day, so you can't see them because of the sun's brightness.)

So, he decided to multiply 29.5 days with the 12 cycles of the moon which gave an even number of 354 days. Because of this even number, he used his power as a King to add an extra day to the calendar to become 355 days. Nevertheless, the problem became even bigger now since the year was short of 57 days. King Numa added 2 more months at the end of the calendar and amassed 29 days to one month which was Jan and 28 days to the other which was February, which became the shortest month of the year.

As time passed, an Emperor named Julius Caesar came into power and brought the solar calendar( A calendar based on the movement of the Earth around the Sun, which defines the year)into picture which had a year made of 365 days.

Remember, the ancient Romans used a calendar based on the moon.

The solar calendar moved January and February to the beginning and made an arrangement by adding extra 10 days to the old calendar to achieve a total of 365 days.

However, since the solar calendar had an extra 6 hours. Recall that it takes the earth 365.24219 days to orbit the sun. Julius Caesar together with astronomer Sosigenes decided to add a day to February every 4 years since it had the shortest days. And that is how the leap year came into existence, and it became known as The Julian Calendar.

Nevertheless, after 1500 years, even The Julian Calendar fell out of sync.

Remember, that a year is short of 0.24219 days and not exactly 0.25 days. Which means that the approximated 6 hours was short of about 11 minutes. Hence, after 1500 years without the 11 minutes being accounted for, the year became short of about 10 days.

Pope Gregory IV decided to work on this problem by replacing the Julian Calendar with the Gregorian calendar which we still use now. So what changes did Pope Gregory IV made?

He decided that we should not have a leap year after every four years.

So how do we know when to add a leap year and to eliminate it?

Here are some rules that guide the decision of whether to add or skip a year.

- A leap year must be divisible by 4. For example, 2020, is a leap year because 2020/4=505.
- A leap year must NOT fall in a year that is divisible by one hundred years ONLY. However, if a year is divisible by BOTH one hundred(100) and four hundred(400), then it a leap year.

Today, the majority of countries in the world use the Gregorian calendar as their sole civil calendar. Countries which do not use the Gregorian calendar include Afghanistan and Iran (which use the Solar Hijri calendar), Ethiopia (Ethiopian calendar), and Nepal (Vikram Samvat).

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