The actual moment in time of noon indicated in this way will vary for people only a few miles apart. Observed time of noon is when the sun is at its highest point in the sky. The term observed time refers to a different method of ascertaining the time that relies on physical observation of things such as the sun, moon or stars, and is not really used these days. It's also possible to convert that to a wall time in another location, such as San Francisco, where someone looking at their computer's time display at the same time would have seen Fri 10 Jun 22:10. If I apply knowledge about how that time relates to UTC (in my case, adjusting by one hour to account for British Summer Time) I can convert that to the incremental time 1465621816590. So, for example, while writing the previous section I may have glanced at the time displayed by my computer and seen Sat 11 Jun 06:10. However, incremental time is not usually seen directly by users, but is typically mapped to a field-based time format for interchange or for human consumption. Most programming languages and operating environments provide or use incremental time for working with time values.
Other systems use different units and/or epochs.įor example, at one point while writing this paragraph the incremental time for JavaScript in my browser was 1465621816590 (ie. Java (and many other systems) count time as the number of milliseconds since midnight (00:00 a.m.) on Januin UTC (less all of the intervening leap seconds). Incremental time is a way of representing time in computers that is based on a progression of fixed integer units that increase monotonically from a specific point in time (called the "epoch").
#Etc utc time zone iso
The formats described by the ISO 8601 standard are field-based. Field-based times are also typically tied to a specific calendar (such as the Gregorian calendar). Contrast this with an alternative way to express the same time, 1465621816590, which is not field-based and is rather hard to read.įield-based times may or may not be tied to either UTC or the local time zone – or they may be indeterminate. When you write a time using a field-based format you divide the date and/or time into separate field values such as year, month, day, hour, minute, second, etc. UTC is often indicated in field-based formats using Z. Among other things, it provides a common baseline for converting between incremental and local time. Universal Coordinated Time (UTC) is the basis for modern timekeeping. There are some subtle differences between the two, but none that the average person would notice. UTC is also known as GMT (Greenwich Mean Time). The document Working with Time Zones provides greater detail on each of these topics, as well as guidelines on handling of times and dates on the Web. This article gently introduces the concepts behind some basic terminology you will encounter when reading other articles that deal with time zones and handling of dates and times on the Web.
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