That is why UTC defines offsets, so we can have 12 AM with an offset of +4 hours from UTC. I’ve explained what UTC is and how it allows us to define dates and times, but countries like to have their wall time noon match with the solar time for noon, so the sun is at the top of the sky at 12 PM. As POSIX time does not handle leap seconds (nor does Python), some companies have defined their own way of handling time by smearing the leap second across the time around it through their NTP servers (see Google time as an example). In Unix-like systems, the most common way to measure time is by using POSIX time, which is defined as the number of seconds that have elapsed the Unix epoch (Thursday, January 1, 1970), without taking leap seconds into account. While the computer doesn’t have an atomic clock inside but uses an internal clock synchronized with the rest of the world via Network Time Protocol ( NTP). With all this background, you should now be able to understand how the operating system is serving time at any given moment. How all this plays together on your computer This allows for accurate measurement of time while introducing leap seconds to ensure that the time does not deviate from UT1 by more than 0.9 seconds. UTC uses the measurement of a second as defined by TAI. That led to the development of Coordinated Universal Time ( UTC), which brought together the best of the both units. This means that we will eventually have our clock noon deviate substantially from the solar noon. This precision is both a blessing and a curse as TAI is so exact that it deviates from UT1 (or what we call civil time). Using atomic clocks in multiple laboratories across the earth, we get the most accurate and constant measure of the second, which allows us to compute time intervals with the highest accuracy. TAIĪs a result, the International Atomic Time ( TAI) was designed to be as precise as possible. GPS triangulation is a good example of a time-sensitive process, in which being a second off results in a completely different location on the globe.
Although this is not a problem for most applications, it becomes a non-trivial problem when we require really precise measurements. Even if this seems precise enough, it still has issues due to the gravitational pull of the moon, tides, and earthquakes, the days change length all year long.
#24 hour utc clock full#
Today, we use stars and quasars to measure how long it takes for the Earth to perform a full rotation around the sun. This gave birth to Universal Time ( UT1), the successor of GMT (Greenwich Mean Time). One of the simplest ways to measure a second is as a fraction of the day, given that we can reliably guarantee the sun will rise and set every day (in most places). We can then use other time references-such as days, weeks, or years-using a calendar standard as multiples of the second (see Gregorian Calendar as an example).
The same way we have standards to measure weight or length that define kilograms or meters, we need an accurate way to define what a ‘ second’ means. The first concept to grasp when working with time is a standard that defines how we can measure units of time. Otherwise, given the complexity of date- and time-related issues, introducing unexpected bugs is easy. datetime is one of those APIs that seems easy to use, but requires the developer to have a deep understanding of what a few things actually mean. When trying to make things work with the datetime module, most Python users have faced a point when we resort to guess-and-check until the errors go away.
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