# Time isn't What you Think it is – How the Earth Moves

If you have made it this far in life, you probably know that the earth spins counterclockwise and that it orbits around the Sun. You may also know that one full rotation of the earth is equivalent to one day, and a full orbit around the Sun is a full year. Well, you would be right, mostly. A day isn't actually 24 hours, it is 24.0000006 hours, and a year isn't actually 365 days, it's 365.2421891 days. You might have expected that these measurements were a little off, but did you also know that September of 1752 was missing 11 days in the British Empire? Timekeeping isn't absolute, and this impressive video below takes us through all of the anomalies of time. It is quite long, but due to its incredible graphics and vastness of information, it's worth the watch.

Long ago, human civilization realized that if everyone kept track of time based on their orientation to the sun, communicating time would be impossible. For example, where you are right now has a meridian, or vertical line stretching to the Earth's poles. When the Sun crosses that meridian during the day it is called 'local apparent solar noon.' This noon is only true for the exact meridian you are on, and people saw the problem with this. Eventually, time zones came about to standardize how people kept track of time.

Let's talk about days. Looking at the Earth's rotation, it makes a full rotation about every 23.9 hours when observed from a distant point, called a sidereal day. However, as you probably know, our days aren't 23.9 hours, they are 24, and this is because the Earth rotates around the Sun. In order for a point on Earth to make a full rotation with the beginning and end at the same point in front of the Sun, it takes on average 24 hours. This is where we get the 24 hour day, but this number is only an average. Since the earth doesn't orbit the sun in a perfect circle, each day changes depending upon location in Earth's orbit. These inaccuracies in actual time meant that programming accurate clocks would be close to impossible. Since clocks kept constant interval time, scientists derived an equation of time to calculate real solar time from actual clock time.

You probably know that a year is around 365.25 days, and this is because that is the precise number of rotations the Earth makes every time it makes a complete orbit around the Sun. This is also why we have leap years. Leap days aren't actually giving you extra days in your life, they are just adjustments on the manmade calendar so that eventually summer doesn't come a season too early, and so on. If America didn't keep leap days when they founded themselves in 1776, then the USA's calendar would be a full 2 months off of the correct solar date.

[Image Source: Wikimedia]

So, time wasn't what you thought it was? Maybe you already knew all this, but either way, the math and theory behind how modern time came about aren't as simple as addition and subtraction. What did you find most surprising to learn about how timekeeping works? Let us know in the comments.