What Are Time Zones?

You may be wondering what time zones really are? They are actually just areas of the earth used to sync time.So, time zones designate the time for a specific area of the planet.

Before time zones, everyone kept their own time. Some areas had different times altogether due to when they set their clocks to begin. There was no standardization to how it was done. So, someone in one country had no real way to determine the time in another country to the east or west.

Say we set a universal time for the entire earth. Since the sun travels around the planet, bringing the light of day to different parts of the world at different times, one country would be in complete darkness during the day. When it was noon for them, it would be midnight for people halfway around the world. Meanwhile, people in another part of the world would see full noon when it was  midnight for them.

So, it is necessary to set times that match daylight and nighttime hours. Otherwise, a farmer in one part of the world, might have his clock set to 6:00 AM right when the sun rose on the day before harvets. While another person might set it for 8:00 PM when the sun sets. If they each set  their clocks on different days, their clocks would not sync up. They would not be able to catch trains, or make appointments! Among other issues.

So, a standard time that is set for each part of the country, allowing time to reflect daylight and nighttime hours is a necessity. Enter the time zone.

How are Time Zones Defined?

There are 25 time zones in the world. Each one is 15 degrees of longitude apart. There are 360 degrees of longitude around the globe. Divide 360 by 15 and you get 25.

Any country or city that falls within that 15 degrees of longitude is considered to be in that time zone.

In some cases, towns or cities that border longitudinal lines can set up their own time zones to avoid common problems with crossing a time zone. This limits confusion and makes life easier for people.

For instance, if your city overlaps two time zones, or is right on that 15 degree longitude line separating a time zone, your city may opt to choose one or the other.

Some countries use time zones with offsets of 30 nd 45 minutes. This is often used to conserve daylight and ensure people are not in the dark at early morning times, or have extra daylight in the winter. There can be other political reasons as well.

How Are Time Zones Named?

Time zones are named in many ways, so there is no single name for any time zone. Each country, some organizations like the Army and Military, and the Aviation Industry, use them in different ways. Learn about how the military names time zones.

The military names time zones with letters. Civilians and other organizations, name time zones with numbers sequentially from -12 to -1,  and 0 – +12. Greenwich Mean Time or GMT, is given the designation of 0, or GMT + 0. It is also called Universal Time, or UTC. Others refer to it as the zero meridian time zone. 

Each time zone is given a sequential number based on how far behind or ahead of GMT or UTC it is. So, each is numbered plus or minus UTC or GMT.

Time zones east of UTC have an incrementally (decreasing by one) negative number. For instance GMT – 1, GMT – 2, and on. This is because each subsequent time zone east is an hour behind Universal Time Zone 0, or Greenwich time.

Each time zone west of GMT is sequentially numbered like GMT +1, GMT +2, etc. since they are an hour ahead.

Why Are Time Zones Numbered with Positive and Negative Numbers (+1, -2. -5 etc.)

Ever received an email with a time stamp like 1:00:00 GMT -5? Wonder what that is?

Time zones are numbered by positive and negative numbers starting at GMT, UTC or the zero meridian time zone, for a reason. It is easy for someone to calculate the time in that area based on the number of the time zone (+ or -).

Let’s say you get an email from someone in Cape Verde, which is UTC -1. It will have a time stamp like 01:01:01 UTC-1:00. Or, 01:01:01 GMT-1:00, depending on which name the server uses. If your time zone is ET (North American Eastern Time), you know your time is UTC-5:00. So, you know they are 4 hours behind you. You can subtract four hours from the time in their email to find your local time they sent that email.