Editing Greenwich Time Signal (section)

==Structure==

{{Listen|filename=Gts_ (bbc)_pips.ogg|title=Greenwich Time Signal|description=The five pips and one beep}}

There are six pips (short beeps) in total, which occur on each of the 5&nbsp;seconds leading up to the hour and on the hour itself. Each pip is a 1 [[SI prefix|k]][[Hertz|Hz]] tone (about a fifth of a semitone above musical [[Scientific pitch notation#Table of note frequencies|B5]]) the first five of which last a tenth of a second each, while the final pip lasts half a second. The actual moment when the hour changes – the "on-time marker" – is at the very beginning of the last pip.<ref>{{cite web|title=What's the time?|url=http://www.rmg.co.uk/explore/astronomy-and-time/time-facts/what%27s-the-time|work=Astronomy & Time|publisher=Royal Museums Greenwich|access-date=5 February 2014|archive-url=https://web.archive.org/web/20140222055748/http://www.rmg.co.uk/explore/astronomy-and-time/time-facts/what%27s-the-time|archive-date=22 February 2014}}</ref>

When a [[leap second]] occurs (exactly one second before midnight [[UTC]]), it is indicated by a seventh pip. In this case the first pip occurs at 23:59:55 (as usual) and there is a sixth short pip at 23:59:60 (the leap second) followed by the long pip at 00:00:00.<ref>{{cite web |title=Leap second: Keeper of the pips |website=BBC News |date=30 December 2008 | url=http://news.bbc.co.uk/1/hi/sci/tech/7791709.stm |access-date=5 February 2014}}</ref> The possibility of an extra pip for the leap second thus justifies the final pip being longer than the others, so that it is always clear which pip is on the hour. Before leap seconds were conceived in 1972, the final pip was the same length as the others.<ref>{{cite web |title=The comforting tone of the hourly radio pips |url=https://www.bbc.co.uk/news/blogs-magazine-monitor-26052087 |website=BBC News (Magazine Monitor) |date=5 February 2014 |access-date=5 February 2014}}</ref> Although "negative" leap seconds can also be used to make the year shorter, this has never happened in practice.<ref>{{cite web|title=Leap years and leap seconds|url=http://www.rmg.co.uk/explore/astronomy-and-time/time-facts/leap-years|publisher=Royal Museums Greenwich|archive-url=https://web.archive.org/web/20140222055800/http://www.rmg.co.uk/explore/astronomy-and-time/time-facts/leap-years|archive-date=22 February 2014}}</ref><ref>{{cite web|title=Adjusting after a 'long' weekend at the Royal Observatory – Precision clocks and the leap second|url=http://blogs.rmg.co.uk/collections/2012/07/06/adjusting/|publisher=Royal Museums Greenwich|access-date=5 February 2014|archive-url=https://web.archive.org/web/20140222055748/http://blogs.rmg.co.uk/collections/2012/07/06/adjusting/|archive-date=22 February 2014}}</ref>

Although normally broadcast only on the hour by BBC domestic radio, [[BBC World Service]] uses the signal at other times as well. The signal is generated at each quarter-hour and has on occasion been broadcast in error.<ref>{{Cite web |title=Greenwich Time Signal - the 'pips' |url=https://www.bbc.com/historyofthebbc/anniversaries/february/the-pips |access-date=2023-03-03 |website=www.bbc.com |language=en}}</ref>