The Future of Leap Seconds

@10u8 writes "Since 1972 precision clocks around the world have ticked using atomic seconds, but earth rotation is slowing down. Leap seconds have been inserted in order to keep noon happening at noon, but they upset some timekeepers. Recent discussions have considered discontinuing leap seconds in UTC, and a colloquium in Torino next month will present results. It is a matter of international significance."

Comments

Why?

[k-0s]

I can't see why they hate leap second. I'll be damned if I am going to eat lunch at what is called 8:00 in the morning because they don't want to keep leap second. Grow up, we have leap years and human time keeping is not an exact science as the Earth tends to spin the way IT wants not the way we want.

Re:Why?

[Bob Fr]

There is time as used by humans vs other measures. Its purpose was to define the time that the trains ran on and is very convenient and has only passing relationshipt to the position of the sun -- those at the edges of timezones can be off by an hour or two or more.

Leap seconds are a fine correction for gear that, unlike humans, cares about nanosecond accuracy.

The serious problem with leapseconds is that they make minutes context sensitive and essentially all computer software presumes seconds are not context sensitive.

The simple fix is to keep leap seconds as a correction factor but not confuse it with the time that humans and their computers use for normal use.

The leap second is the kind of bug that appears when you have experts who know too much and are totally clueless about any usage other than what the care about.

It was simply a stupid mistake to foist it on humans and there. They should apologize and simply keep their mitts of social mechanisms like the clock.

Re:Why?

[Guppy06]

One word: Longitude. Generally speaking, you determine your longitude by comparing what the local solar time is (determined by looking at the position of the sun in the sky) and comparing it to the time in some reference point (say, the Prime Meridian). Every hour's difference is 15 degrees of longitude.

Obviously, there have been all sorts of tweaks and modifications to this formula in the past 200+ years or so, but the basics are the same: You need to know what time it is to know where you are. Your precious little GPS receivers wouldn't work if they could get as accurate a time measurement as possible from the US Naval Observatory.

(Some historians have suggested that the US won the war in the Pacific because US ships had more accurate clocks.)

What are leap seconds?

[Phroggy]

Leap years work like this:

One year = the time it takes for the Earth to revolve around the Sun.
One day = the time it takes for the Earth to rotate on its axis.

The problem is, there are really about 365-1/4 days in a year - it doesn't work out evenly to 365 days. So, every four years we add an extra day (Feb. 29), and then it all averages out. Otherwise, if we only had 365 days in a year, over many years seasons would start getting earlier and earlier on the calendar.

One day = the time it takes for the Earth to rotate on its axis
One second = the time it takes for Cesium 133 to oscilate about 9.19 billion times (because it's something constant we can measure)

The problem, again, is that there aren't exactly 86400* seconds in a day. So, we add leap seconds periodically to account for it. As I understand it, this isn't necessarily done at fixed intervals, but rather whenever it's decided that it needs to be done. The Network Time Protocol used to synchronize clocks over the Internet supports leap seconds; they can be announced over NTP in advance, so everybody adds them at the correct moment.

Why is it important? It's not important to most people, but computers like things to be precise and accurate for various reasons, and that means we have to agree on exactly what time it is.

* BIND now lets you write "1d" in a zone file, but how many of you still have this number memorized? ;-)