Eastern Time Zone
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Eastern Time Zone (ET) is a time zone used in the eastern regions of North America, including parts of the United States, Canada, and some countries in the Caribbean and Central America. Standard time (Eastern Standard Time, EST) is UTC−05:00, meaning the time is five hours behind Coordinated Universal Time (UTC).
Most areas in this zone observe Eastern Daylight Time (EDT) during summer, which is UTC−04:00. This change is known as daylight saving time: clocks are set one hour forward in June and returned to standard time in the fall. Major cities in this zone include New York, Washington, Toronto, and Montréal.
Geographic boundaries
Within the United States, the zone covers Atlantic coastal states such as New York, Pennsylvania, Virginia, Georgia, and much of Florida, as well as some inland states such as Ohio and Michigan. In Canada, it covers much of Ontario and Québec. The zone's boundary does not follow meridian lines precisely; states and provinces adjust their borders to suit commerce and transportation needs.
Scientific basis
The zone is based on the meridian at 75 degrees west, which is five hours behind the Greenwich meridian (0°). The time zone system emerged from railroad operations in the nineteenth century, when railway companies and governments needed a uniform schedule to replace the local solar time that varied by city.
Technical use
Computer systems identify this zone using IANA database names such as "America/New_York" and "America/Toronto". These names encode the history of time changes, allowing software to calculate past times accurately.