AM and PM Explained
How does the 12-hour clock system work? Is midnight 12 am or 12 pm? more
How does the 12-hour clock system work? Is midnight 12 am or 12 pm? more
Daylight Saving Time (DST) is the practice of setting the clocks forward one hour from standard time during the summer months, and back again in the fall, in order to make better use of natural daylight. more
Coordinated Universal Time (UTC) is the basis for civil time today. This 24-hour time standard is kept using highly precise atomic clocks combined with the Earth's rotation. more
History of Daylight Savings Time (DST). Who invented it and in what year? What is the purpose of having a time change every year and when did Daylight Saving Time start? more
Which way do the clocks go? "Spring forward or fall back" is just one way to remember which way set the clocks for Daylight Saving Time (DST). more
Greenwich Mean Time (GMT) is often interchanged or confused with Coordinated Universal Time (UTC). But GMT is a time zone and UTC is a time standard. more
Daylight Saving Time (DST) has been used for more than 100 years. But do the pros really outweigh the cons? more
The UK is not on Greenwich Mean Time (GMT) all year. During Daylight Saving Time the correct time zone is British Summer Time (BST). more
Standard time is also known as winter time or normal time in some countries. more
When Daylight Saving Time starts, we lose an hour. When it ends, we gain an hour. So what hour repeats? What time is it before & after? Explanation with DST example. more
The International Date Line (IDL) is an imaginary line on Earth's surface located at about 180 degrees east (or west) of the Greenwich Meridian. more
A time zone refers to any region where the same standard time is kept. Interactive Time Zone Map for current time zones worldwide. more
International Atomic Time (TAI) is one of the main components of Coordinated Universal Time (UTC), the time scale used to determine local times around the world. more
In most of the USA, Daylight Saving Time starts on the 2nd Sunday in March and ends on the 1st Sunday in November—but there are exceptions. more
“Daylight Saving Time” is the correct term, but “Daylight Savings Time” with an “s” is at least as commonly used. more
Daylight Saving Time (DST) was first adopted in Europe by Germany in 1916. more
Noon is at 12 o'clock but solar noon can be at a different time. What's the difference between the two? more
The expansion of transport and communication during the 19th century created a need for a unified time-keeping system, and time zones were introduced. more
Why doesn't the year's earliest sunset occur on the winter solstice, even though it is the shortest day of the year in terms of daylight? more
Summer time is often used to describe Daylight Saving Time (DST), especially the United Kingdom. Winter time instead of standard time is also a common variation. more
Universal Time is a solar time standard used in astronomy and to define time on Earth. How is it measured? What's the difference between UT, UT0, UT1, UT2, and UTC? more
In terms of solar time, most days are a little longer than 24 hours. Exact day length for today and yesterday. more
The abbreviation for Coordinated Universal Time is UTC. Why is it not abbreviated as “CUT” or “TUC”? more
The term time zone can be used to describe several different things. more
When did the 3rd millennium and 21st century begin: on New Year's Day 2000 or 2001? Did the anno domini time reckoning start with year 1 or year zero AD? more
Atomic clocks are among the most accurate timekeepers in human history. Just how precise are they and how do they work? more
Use a sundial to determine the time of day and you will probably be off by a few minutes. That's where LMT comes into play. How is it measured and what is it used for? more
Every now and then a leap second is added to Coordinated Universal Time (UTC) in order to synchronize clocks worldwide with the Earth's ever-slowing rotation. more
Out and about at night without a watch or a smartphone readily available? If you are in the Northern Hemisphere use the Big Dipper and the North Star to tell the time. more
Organizations and individuals have for many years argued about abolishing leap seconds for good. more
The Revised Julian calendar is one of the most accurate calendar systems ever developed. How does it work, and why don't we use it? more
The definition of a tropical year is the time it takes the Earth to complete a full orbit around the Sun. It is approximately 365.242189 days long. more
Leap seconds have been added to clocks worldwide since 1972. Why are they needed and why the Earth is slowing down? more
Astronomers use other measures of time, such as Terrestrial Time (TT), which is 32.184 seconds ahead of International Atomic Time (TAI). more
Winter time is often used to describe the time of year when a country is not on Daylight Saving Time (DST). It is officially known as standard time. more
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