How Time Zones Are Coordinated?
Around this time of year, many places in the Northern Hemisphere "spring forward" into daylight saving time, moving their clocks ahead one hour to realize sunnier skies in their evening times. On different days throughout the Southern Hemisphere, many similarly wind back their clocks to brace for the winter months ahead. While this annual ritual is standard for many, some locations this year won't adopt daylight saving time as they previously did, and other places will do it differently than before.
One of the most fascinating aspects of these time changes is that for many people they are fully automatic. Billions of devices around the world will automatically change without their users lifting a finger. Airline schedules will instantly adapt, calendar invites will silently adjust. The sleep-deprived will probably see "01:59" one minute, and "03:00" the next.
How is it possible for all these changes to happen seamlessly? The Time Zone Database, part of the Internet Assigned Numbers Authority (IANA) responsibilities of ICANN, is a community collaboration that forms the foundation of this synchronicity. Let's explore how it works.
What is the Time Zone Database?
The Time Zone Database is fundamentally a machine-readable description of the time zones used in locales across the world, including when transitions to and from daylight saving time occur. It contains an exhaustive set of mathematical rules that govern these transitions. Users of computers, phones, and web applications either select their location in their time settings, or sometimes find themselves automatically geolocated, and based on that location these rules do the rest of the work.
The rules cover not just the current time, but historical time adjustments and projected adjustments in the future. The database also records leap seconds, which are small adjustments made to account for irregularities in the Earth's rotation. The formal scope of the project is to faithfully record times from the year 1970 onward, so you can find out, for example, exactly when the 1985 Live Aid concert started for someone watching from Rio de Janeiro. However, the database contains historical data from before then as well.
How is the database maintained?
While IANA hosts the project, and is responsible for distributing the data, the curation of the time zone data is performed by a community of experts and interested observers convened through an IANA discussion forum. This group evaluates reports of changes to time zone policy, assesses the provenance of any proclamations, and if an update to the database is necessary, makes sure the changes are accurately recorded.
This group is led by volunteer Time Zone Coordinators, who organize the editorial reviews and make any final adjudications based on the group's review. The entire project originated with Arthur David Olson, who served in this role for many years. Today, Dr Paul Eggert and Tim Parenti lead this group.
How are time zone policies changed?
The time zone in any given location is essentially the time that people in that area set their clocks to. The time zone database seeks to reflect this "ground truth" through documenting sufficient evidence to confirm what time people adhere to. In most situations, this ground truth is set through applicable laws and regulations, which are defined by governments.
In addition to providing a home for the database, IANA also plays an educational role for policymakers. Through ICANN's global engagement capabilities, IANA helps educate policymakers on the need to make time zone changes in a way that minimizes potential negative technical impacts.
One of the important facets of this work is recognizing that, even if the Time Zone Database is updated with a new policy, propagation of the updated data can take many months, even up to a year or two. Most devices do not immediately retrieve the updated mathematical rules directly from IANA. Instead, software vendors retrieve the data, implement the changes into their software, and then distribute it to their customers through software updates. The latest changes may not be available to you until you install the latest system update to your computer or phone.
Because of this propagation time, it is crucial that policymakers provide a year or more advance notice to IANA before changes to their time zone policies take effect. Without this lead time it is almost guaranteed there will be great confusion caused by the use of inconsistently distributed time zone data.