Articles About Timekeeping (38)
AM and PM Explained
How does the 12-hour clock system work? Is midnight 12 am or 12 pm?
UTC – The World's Time Standard
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.
UTC & GMT – Same Difference?
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.
Daylight Saving Time (DST)
Why do many countries set the clocks back and forth an hour twice a year?
What Is a Time Zone?
A time zone refers to any region where the same standard time is kept. Interactive Time Zone Map for current time zones worldwide.
When Did the 21st Century Start?
When did the 3rd millennium and 21st century begin: on New Year's Day 2000 or 2001? Do we count from year 1 or year 0 AD? What century are we in?
GMT or BST in the UK?
The UK is not on Greenwich Mean Time (GMT) all year. During Daylight Saving Time the correct time zone is British Summer Time (BST).
What Is the International Date Line (IDL)?
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.
International Atomic Time
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.
What Is Solar Noon?
Noon is at 12 o'clock but solar noon can be at a different time. What's the difference between the two?
History of DST
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?
What Is Standard Time?
Standard time is also known as winter time or normal time in some countries.
When Do Decades Start?
Does the year 2020 mark the beginning of a new decade, or do we have to wait until 2021 to celebrate the beginning of the twenties?
Transition to DST
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.
Why UTC – not CUT?
The abbreviation for Coordinated Universal Time is UTC. Why is it not abbreviated as “CUT” or “TUC”?
What Is Universal Time?
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?
1 Hour Ahead or Back?
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).
How Long Is a Day on Earth?
In terms of solar time, most days are a little longer than 24 hours. Exact day length for today and yesterday.
Timekeeping by Stars
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.
What Are Leap Seconds?
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.
Why Do We Have Time Zones?
The expansion of transport and communication during the 19th century created a need for a unified time-keeping system, and time zones were introduced.
How Does an Atomic Clock Work?
Atomic clocks are among the most accurate timekeepers in human history. Just how precise are they and how do they work?
What Is Local Mean Time?
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?
The Never Ending DST Debate
Daylight Saving Time (DST) has been used for more than 100 years. But do the pros really outweigh the cons?
Equation of Time
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?
DST in the United States
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.
What is Internet Time, and how to convert between the time zones and beats.
Daylight Savings or Saving?
“Daylight Saving Time” is the correct term, but “Daylight Savings Time” with an “s” is at least as commonly used.
A Year Is Never 365 Days
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.
The Revised Julian Calendar
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?
What Is a Time Zone?
The term time zone can be used to describe several different things.
Summer Time or DST?
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.
Winter Time Is the Same as Standard Time
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.
The Future of Leap Seconds
Organizations and individuals have for many years argued about abolishing leap seconds for good.
History of Daylight Saving Time in Europe
Daylight Saving Time (DST) was first adopted in Europe by Germany in 1916.
How Leap Seconds Work
Leap seconds have been added to clocks worldwide since 1972. Why are they needed and why the Earth is slowing down?
Alternative Time Systems
Astronomers use other measures of time, such as Terrestrial Time (TT), which is 32.184 seconds ahead of International Atomic Time (TAI).
Length of Tropical Years 1900–2100
Exact length down to the second of tropical years ranging from 1900 to 2100. It is also known as a solar year, astronomical year, or equinoctial year.