Time fact files
Find out about the many types of time: atomic, universal, civil, local, sidereal and solar.
Harrison's marine timekeepers are the centrepiece of a permanent display at the Royal Observatory.
At 01.00 GMT on the last Sunday in March, UK clocks go forward 1 hour (start of BST), and back on the last Sunday in October.
The seasons are divisions of the year which relate to the annual changes in the weather.
Find out about equinoxes and solstices and why they don't always occur on the same dates every year.
The Road Vehicles Lighting Regulations 1989 make the use of front and rear lamps compulsory on vehicles between sunset and sunrise.
The measurement of time no longer uses sundials but relies on devices, such as clocks, to determine a uniform rate.
A calendar is a system of reckoning the time over extended intervals by combining days into longer groupings.
Times of first sighting and setting of the new crescent moon at the start and end of the Islamic holy month of Ramadan.
Leap years are inserted to bring the average length of the calendar year into line with the tropical year.
Nowadays we can easily find out the time by looking at a watch or clock, but it has not always been so easy.
BBC radio has been broadcasting the six-pip time signal since 1924.
The bright red Time Ball on top of Flamsteed House is one of the world's earliest public time signals.
The earliest known sundial, found in Egypt, dates from at least 3,500 years ago.
The Chinese Year of the Horse starts on 31 January 2014. Find out more about the Chinese luni-solar calendar.
The first day of the Islamic New Year in 2008 is 10 January (1 Muharram, 1429 AH). Find out more about the Islamic (Hijri) lunar calendar...
Easter is usually said to be the first Sunday after the first Full Moon on or after the Vernal Equinox, but the true definition is more...
Answers to all your questions about the start of the new Millennium and the first sunrise of the year 2000.
2007 marked 100 years since British Summer Time was first proposed. But why change the clocks, which way and whose idea was it?