When you cross the IDL, the day and date change. If you cross it traveling westward, the day goes forward by one, and the date increases by one. If you cross it traveling eastward, the opposite occurs.

The International Date Line

The International Date Line (IDL) is an imaginary line that runs from the North Pole to the South Pole, mostly along the 180° longitude line in the Pacific Ocean. It serves as the demarcation line between two consecutive calendar days. The purpose of the IDL is to account for the Earth's rotation and to ensure that each day begins and ends at the same time across the globe.

Time and Date Changes

As a person crosses the International Date Line, there are significant changes in both time and date. These changes occur due to the difference in longitude.

Eastward Travel
When moving eastward across the IDL, the clock moves ahead by 24 hours. This means that if it is Thursday in the western hemisphere, it will be Friday on the other side of the line. The day and date skip ahead by one day.

For example, if a person leaves Honolulu, Hawaii, on a Tuesday morning and travels eastward towards Japan, they will cross the International Date Line. As a result, they will lose a day, and when they arrive in Tokyo, it will be Wednesday.

Westward Travel
On the other hand, when traveling westward across the IDL, the clock moves back by 24 hours. This means that if it is Friday in the western hemisphere, it will be Thursday on the other side of the line. The day and date move back by one day.

For instance, if a person departs from Tokyo, Japan, on a Monday morning and travels westward towards Honolulu, Hawaii, they will cross the International Date Line. As a consequence, they will gain a day, and when they arrive in Hawaii, it will still be Monday.

Effects on Travel and Communication
The International Date Line can have significant effects on travel and communication. For example:
- It can cause confusion for travelers, as they may need to adjust their schedules and plans due to the time and date changes.
- It can lead to situations where a person celebrates their birthday twice or skips it altogether, depending on the direction of their travel.
- It can impact international business transactions, as parties in different time zones may need to coordinate their activities carefully.
- It can affect real-time communication, such as phone calls or video conferences, as individuals on opposite sides of the IDL may be experiencing different days.

In conclusion, the International Date Line marks the transition between calendar days. When crossing the line, time and date changes occur, with the clock moving ahead when traveling eastward and moving back when traveling westward. These changes can have various implications for travel, communication, and daily routines.

If you go east to west of the IDL you gain day


If you go west to east of the IDL you loss night