When the sun rises in the morning in the Chicago around 6:30 am, people in New York are getting ready for work around 7:30 am. People in Los Angeles are probably still sleeping as it is 4:30 am there. People in London might just be finishing lunch because it is 1:30 pm, while people in Japan are getting ready to go to bed as it is 9:30 pm. All of this is happening at the same exact moment that the sun is rising in Chicago. But how does that happen? This is all thanks to time zones!
So what is a time zone?
Time zones are areas that have a certain set time that fits into relation as the sun passes over it. Because there are 24 hours in a day, there are 24 times zones. However, depending on location, there are some time zones that are different by 30 minutes or even 15 minutes. So in total, there are actually about 40 time zones. To see how this works, this map shows where the sun is shining and where the Earth is dark at the exact moment that it is looked at. In the United States, there are actually nine time zones, though most people live within the four time zones of the continental United States. People who live around the eastern coast of the United States live in the Eastern Standard Time (EST) zone, while people who live in between the EST and the Rocky Mountains, live in the Central Standard Time (CST) zone. People who live around the Rocky Mountains live in the Mountain Standard Time (MST) zone, and people who live on the west coast live in the Pacific Standard Time (PST) zone. In Alaska, people live in the Alaskan Standard Time (AKST) and in Hawaii, people live in the Hawaii-Aleutian Standard Time (HST). While other time zones do have special names like the time zone in the United States, some time zones are known just by the number of hours different they are from the Coordinated Universal Time (UTC).
What is Coordinated Universal Time?
On a world map, a little part of England sits at the center part of the map, especially a place called Greenwich. All time zones measure from this town in England. So for example, Chicago would be considered UTC -6, which means that Chicago's time is six hours behind Greenwich's time. On the other hand, Sydney, Australia would be considered UTC +10 or ten hours ahead of Greenwich's time. Because Greenwich is so important for time zones, sometimes the UTC is called Greenwich Meridian Time (GMT) and people will write things like GMT -6 instead of UTC -6. However on the exact opposite side from Greenwich on a globe, there is another line that divides the day. This is called the International Date Line. The International Date Line makes things really confusing because if a person was to walk from UTC +12 to UTC -12 which sit right beside each other, the person would have walked back in time to the day before! Also, some places like in the United States use something called Daylight Savings Time. This means that at a certain time in the year, clocks are changed by an hour to help keep the times the same with the sun. In the Spring, an hour is usually added to the time, and then in the Fall the time goes back an hour, hence the phrase, "Spring forward, Fall back". This became really helpful for farmers who wanted to have more time during the day to work on the farm, and also people were able to enjoy the daylight longer.
How did time zones get started?
Back in olden times, people used sundials to rely on time. And then when clocks were made, people used those, but clocks were still set to the time sundials. So clocks everywhere were a little different from each other. Within towns and local places this kind of practice was okay, and many people had systems that were called "local time" systems. However, when railroads and telegraphs appeared, things started to get kind of confusing. Trains could never be quite on time, because everywhere they went the time was different. If a telegraph was supposed to be sent at a certain time to another place, it could arrive too late simply because the local times were different. Because of this, the first time zone appeared on the island of Great Britain in 1847, and it relied on Greenwich's time. This really helped trains to be more efficient, although many clocks in England still today have an extra hand on their clock that tells the local time that was used in the past. Then in 1883, the United States created four standard time zones to help ease the confusing system of time that the railroads had at the time. Soon after that, the world was divided into hourly time zones which made world-wide communication much easier. This also helped with world-wide travel when planes appeared.
What happens when someone travels between time zones?
When someone travels say from Chicago to New York, which is only different by an hour, not much happens. However as the difference between time zones becomes bigger, so do the effects. For example, someone who travels from New York to Los Angeles, which is a 4 hour difference, may start feeling very sleepy around 6:00 pm because normally for that person, it would be 10:00 pm. And someone who travels from Los Angeles to New York, might still be very awake at midnight, because normally that would only be 8:00 pm for them. However, when someone travels to a new continent, these effects get much worse. So much so that people came up with a name for it, which is jet lag. If someone from the United States traveled to Japan for example, they would want to sleep all day and be unable to sleep at night, even if they are very sleepy. After a while, people eventually adjust to the time differences but the greater the difference in time zones, the longer it takes someone to adjust.
Time zones are really interesting between countries and are really helpful for people to keep time. They make travel and communications much easier to figure out than if there were no time zones, though sometimes time zones can still be confusing. If business people want to communicate with partners around the world, not only do they have to schedule a time that works for them, but also find an appropriate time for their business partners. If someone in Chicago plans a meeting for 1:00 pm, and they meet on the phone with someone in Germany and someone in New Zealand, the partner in Germany would be meeting at 9:00 pm, and the person in New Zealand would be meeting at 7:00 am the next day! So keeping time zones in mind while communicating and traveling is really important.
- Day and Night World Map
- World Time Zone Map
- Time Zone Converter
- A Walk through Time: World Time Scales and Time Zones
- Facts and Figures about Time Zones
- Learn more about the United States time zones
- Universal Time
- What is UTC?
- What is UTC Time?
- Astronomical Times
- Time, what Time?
- A Traveler's Guide to the International Date Line
- Samoa, Tokelau Cross International Dateline
- Daylight Saving Time: Rationale and Original Idea
- Saving Time, Saving Energy
- Economics of Time Zones PDF
- A Brief History of Time Zones
- The Times Reports on "The Day of Two Noons"
- Bristol Time
- Jet Lag
- Jet Lag and Sleep