Time fact files

Time

Find out about the many types of time: atomic, universal, civil, local, sidereal and solar.
John Harrison and the Longitude problem

Harrison's marine timekeepers are the centrepiece of a permanent display at the Royal Observatory.
The Seasons

The seasons are divisions of the year which relate to the annual changes in the weather.
British Summer Time (BST)

At 1.00 am GMT on Sunday 25 October 2009 the clocks will move back by an hour. Find out more about BST in our fact file.
Lighting-up time, sunrise/sunset and twilights

The Road Vehicles Lighting Regulations 1989 make the use of front and rear lamps compulsory on vehicles between sunset and sunrise.
Equinoxes and solstices

Find out about equinoxes and solstices and why they don't always occur on the same dates every year.
The equation of time

The measurement of time no longer uses sundials but relies on devices, such as clocks, to determine a uniform rate.
The calendar

A calendar is a system of reckoning the time over extended intervals by combining days into longer groupings.
The date of Ramadan

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 and leap seconds

Leap years are inserted to bring the average length of the calendar year into line with the tropical year.
What's the time?

Nowadays we can easily find out the time by looking at a watch or clock, but it has not always been so easy.
The 'six pips' and digital radios

BBC radio has been broadcasting the six-pip time signal since 1924.
The Greenwich Time Ball

The bright red Time Ball on top of Flamsteed House is one of the world's earliest public time signals.
Sundials

The earliest known sundial, found in Egypt, dates from at least 3,500 years ago.
Chinese New Year and the Chinese calendar

The traditional Chinese luni-solar calendar is used for religious purposes and for agriculture.
The date of Easter

The simple definition of Easter is that it is the first Sunday after the Full Moon that occurs on or after the Vernal Equinox.
Al Hijra and the Islamic 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 in our fact file.
The new millennium

Answers to all your questions about the start of the new Millennium and the first sunrise of the year 2000.
Spring Forward: 100 years of British Summer Time

2007 marked 100 years since British Summer Time was first proposed. But why change the clocks, which way and whose idea was it?

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