12pm doesn't exist

[backontrack]

Technically, you could say that there is no such thing as time itself, and you could explain this by saying that it's just something humans invented to measure what has happened or to plan things...but that gets very confusing, so I wouldn't recommend it.

Although, going down that path, creating and using a time system that utilises values that don't actually exist is just typical of humanity. :roll:

 

[backontrack]

2400 should not be used for the simple reason of the seconds that follow. If 24:00.00 is valid then it's followed by 24:00.01, .02, etc and by convention there aren't more than 86400 seconds in a day.

Actually, a full day on Earth is actually more like 23 hours and 56 minutes I think - so we round it up, presumably because that's much more sensible than faffing around with completely new measurements.

 

[najaB]

Actually, a full day on Earth is actually more like 23 minutes and 56 seconds I think - so we round it up, presumably because that's much more sensible than faffing around with completely new measurements.

Yeah. That's why I said 'by convention' - the 24 hour day is 'close enough' for most people.

 

[edwin_m]

Actually, a full day on Earth is actually more like 23 minutes and 56 seconds I think - so we round it up, presumably because that's much more sensible than faffing around with completely new measurements.

I'm assuming you mean 23 hours and 56 minutes, but even then the clocks would need adjusting every couple of weeks to prevent sunrise and sunset drifting noticeably out of sync with when the clock says they should be.

In actual fact a "leap second" is added to keep clocks in synchrony with the earth, but it's only needed every few years. I think there is provision to deduct a second as well but it's never been needed. The rotation of the earth is very gradually slowing so the modern definition of time units (chosen to match historical values) is ever so slightly shorter than it would be if we were defining them from the earth's motion today.

According to Wikipedia the leap second is added at midnight and displayed on clocks as 23:59:60. Which opens up a whole new can of worms...

https://en.wikipedia.org/wiki/Leap_second

 

[Peter Mugridge]

It's the leap year every four years which keeps that rogue 4 minutes a day in check; the occasional leap second is just fine tuning applied when required.

 

[adrock1976]

It's the leap year every four years which keeps that rogue 4 minutes a day in check; the occasional leap second is just fine tuning applied when required.

Of course, another variable is regarding leap years is that for years that end in a hundred, there is no leap year unless it is also divisible by 400 as well as 4.

For example, the years 2016 and 2020 are clearly divisible by 4, so are leap years. The years 1900 and 2100 although are divisible by 4, they are however not divisible by 400, so are not leap years. On the other hand, the year 2000 is divisible by both 4 and by 400, so was a leap year.

 

[me123]

Mathematician Matt Parker has a great video about leap years, and a proposal to refine the system even further.

[youtube]qkt_wmRKYNQ[/youtube]

 

[tony_mac]

It's the leap year every four years which keeps that rogue 4 minutes a day in check; the occasional leap second is just fine tuning applied when required.

No, the leap year is because there aren't exactly 365 days in a year; it has nothing to do with the length of a day itself. If we didn't adjust the length of the day, then it would eventually be light at midnight etc. adding a whole day doesn't change that.

A day is only 23 hours and 56 relative to some fixed point. Because the earth is also moving around the sun, it takes 24 hours for the same point to be facing the sun (it varies throughout the course of the year, but is almost exactly 24 hours on average, hence the relative lack of leap seconds)

 

[edwin_m]

A day is only 23 hours and 56 relative to some fixed point. Because the earth is also moving around the sun, it takes 24 hours for the same point to be facing the sun (it varies throughout the course of the year, but is almost exactly 24 hours on average, hence the relative lack of leap seconds)

Ah yes, I knew that came from somewhere. I think it's known as a sidereal day, and is used by astronomers because it's when that star they were looking at last night will be in the same place again.

 

[cb a1]

Many years ago I worked in an office for a large bakery. A manual clock in / clock out machine and someone had to work out how many hours and minutes the staff worked a week. This was still done manually and frequently given to me to do. Whilst I became a dab hand at calculating the number of minutes and hours worked for something like: In 08:42 Out 12:06 In 13:11 Out 17:02, I wished that decimal time existed.

Thanks to Wikipedia I discovered ... decimal time. I propose we adopt this and stop the confusion

 

[Muzer]

It seems to be fashionable to count from zero these days - makes sense with time but when counting items it seems to have the major defect that if you count to five you've actually counted six things!

Counting from zero (or more correctly, indexing from zero — counting is still done as it always was) is common in computer science. I'm not sure if that has spread into the real world from technical people or if it's another issue. But it does make sense from a computer science perspective — the classic example is that a series of data items can be represented by the memory address of the first item as well as an index. Then, adding the index times the size of a data item will give you the address of the item at the given index — but since the memory address is that of the first item, this only works when the indices start from zero, as you need to add zero to the memory address of the first item to get back the memory address of the first item!

 

[edwin_m]

British Rail was obviously an early pioneer of computer science. Pre-TOPS the first of class was generally given a number ending in zero whether steam or diesel. But when TOPS was introduced all numbers within a class started from 1. If the first of class still existed it was given a convenient vacant number or became the last in the number series.

 

[tsr]

As an aside, I am aware of at least one permanent schedule for a train which shows a stop as having a departure time of 00.00 on crew diagrams (but sometimes not on websites using open source data).

However, it's a set-down-only stop and therefore it shouldn't result in public confusion. In fact, it's actually usually indicated as 00D00, where "D" means set-down-only, but that's probably irrelevant.

 

[Mutant Lemming]

Will the increasing heat from the sun effect the speed of which this planet moves around it and thus affect our current timings ? ..and would it make any difference to the Thameslink timetable or their ability to produce 4 car trains for the height of the peak hour ?

 

[najaB]

Will the increasing heat from the sun effect the speed of which this planet moves around it and thus affect our current timings ?

No. But the Moon moving away from the Earth will. As it moves away it robs the Earth of some angular momentum.

 

[Mutant Lemming]

No. But the Moon moving away from the Earth will. As it moves away it robs the Earth of some angular momentum.

Will it stretch 4 car 319s in to 8 cars though ?

 

[najaB]

Will it stretch 4 car 319s in to 8 cars though ?

Sadly, no. Not even astrophysics* can manage that one.

*Yes, I know it's orbital mechanics but astrophysics sounds cooler

 

[Mutant Lemming]

Sadly, no. Not even astrophysics* can manage that one.

*Yes, I know it's orbital mechanics but astrophysics sounds cooler

...and here was I was hoping to meet the Jetsons one day on the 06:52 to St.Pancras

 

[najaB]

Just realised another 'problem' with 2400 being valid - it breaks the world. If you're standing on the International Date Line then 2400.00 breaks the calendar as it would be the same day on both sides of the line.

 

[Strat-tastic]

"Nothing happens at midnight on the Railways"

is an old saying that I've heard quoted a few times.

Try reading the 'Are Our Railways Hanuted?' thread!

 

[Bertie the bus]

12pm means noon as you well know.

If you're so correct and it's pedant o'clock (pm), why aren't you using colons? You're portraying numbers/pricing, not time.

I have to say I also considered this thread a pointless pedantic rant until I visited Liverpool South Parkway and the Scousers seem to agree, 12 PM doesn’t exist, but there are two 12 AMs.