Misconceptions of noon?

A plea for consistent and coherent labelling of times

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Keith S. Taber

Stardate: -297795.016615931

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To call noon either 'before noon' (a.m.) or 'after noon' (p.m.) is a crime against good nomenclature.

I saw a reference to a webinar for teachers, 'Teaching Organic Chemistry with videos', on a social media site, and thinking it looked useful was tempted to retweet the message. However, I thought I should do some due diligence first in case I was about to promote somethings dodgy. (That sounds a little paranoid, but as I routinely get invited to contribute to dubious 'predatory' conferences and journals, I try not to take anything on-line at face value).

Checking the website, I found the webinar was being offered several times to suit people in different parts of the world – which seemed very useful.

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However, I then noticed that two of the sessions were scheduled for 12 PM in their local time zones. But what is 12 PM? Perhaps that is pretty basic and everybody (apart from me) knows. To my mind the term 12 PM must mean 12 midnight (as I explain below), but that seemed as unlikely choice of webinar time. Checking some websites, it seems the conventional take is that 12 PM means 12 noon: but that is both an inconsistent, and indeed self-contradictory, idea.

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The 24 hour clock

Of course all such uncertainty is avoided by using the 24 hour clock. The hours then run sensibly through 00.00, 01.00, 02.00, 03.00…10.00, 11.00, 12.00, 13.00, 14.00…21.00, 22.00, 23.00, (24.00 which re-sets as) 0.00.

The 24 hour clock avoids ambiguity, unlike the 12 hour version which runs twice a day. Often there will be enough context in communication for this not to be problematic…

• meet me at 11 of the clock (11 o'clock) for morning coffee
• shall we lunch at 1 o'clock
• the after-work meeting will start at 6 o'clock
• I'll be getting home from work about seven-thirty

…unless you do not realise your interlocutor works night shifts!

But in this era of the global village, a colleague from the other side of the world who tells you they will be contacting you at seven o'clock could easily mean either seven in the morning or seven in the evening. So, distinguishing 07.00 from 19.00 is useful.

Now, it might seem that the 24 clock is not needed if we always specify whether a time is a.m. or p.m. – ante meridiem or post meridiem. Well, perhaps, but as I argue below I really do not think that can work for 12 noon. ('Meridiem' comes from the Latin for noon or midday.)

We might wonder why we run the hours twice in a day, and do not simply use a single count each day. And here, we need to be careful to acknowledge potential ambiguity in the word 'day 'itself – which often means a 24 period, but is also used in contrast to night, as in the idiom "like day and night" *. And in terms of that ambiguity, we might note that traditionally there were 12 hours in the day. For our double daily cycle of hours is historically contingent – that is, it is a hang over from a different time (sic).

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12 hours of daylight, 12 hours of nighttime, 12 hours of sunset

These days we (nearly) all have 24 hour electricity ¹, so it can be as bright as we like any time of day or night. But only a few centuries ago the ambient light levels affected people's lives much more. Even if a fire gave off light inside the home, there were no streetlights, and so being outside at night was more of an event.

Students of British social history will have heard of the Lunar Society that operated around Birmingham at the time when the industrial revolution was underway, and that included such luminaries (luniaries?) as the chemist Joseph Priestley, the potter and industrialist Josiah Wedgwood (grandfather of Charles Darwin), Matthew Boulton and James Watt (producers of Boulton & Watt steam engines), and the physician, poet, and evolutionary speculator Erasmus Darwin (the other grandfather of Charles Darwin).

The group were not called the Lunar Society from astrological sensibilities, but because they met on the day of the full moon each month – for the perfectly pragmatic reason that before street lighting it was very easy to have accidents travelling after dark, and the night of the full moon had the best chance (British weather notwithstanding) of a safe level of natural illumination.

So, for most of human history (and all of its prehistory) the distinction between day and night was even more significant than it is today. So it became common to keep time separately in these two periods. The 'day' was divided into 12 equal parts – hours, and the night was also divided into twelve equal hours. That involves a very different organisation to that we are familiar with today.

The day began at dawn, and after twelve hours of day, night begins at dusk, and then after twelve hours of nighttime another dawn brings the new day. Measuring the start of a new day by the rising or setting of the sun is still practiced today in some communities – so the Jewish and Islamic day starts at nightfall. (In the Biblical account of the creation evening is mentioned before morning, suggesting a mythical first day started with the evening).

But clearly, with this system, the day and night are only of equal duration at the equinoxes. During the Summer the daylight hours last much longer than the nighttime hours and in the Winter the nighttime hours last much longer than the daytime hours (given that there are twelve of each). That is possible because an hour was not directly tied to the Earth's rotation (1 hour = ¹/₂₄ of a day) but was one twelfth of the daytime, or of the nighttime, at that particular point in the year.

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Unequal hours – an alternative conception ²

These 'unequal', 'temporal' or 'seasonal' hours were then not of a fixed duration. At an equinox an hour was much like our modern hour. So, at the vernal equinox the hours all matched up. But the daytime hours then got longer as the Summer solstice approached, with a corresponding shortening of the nighttime hours. Then the daytime hours shortened, with a corresponding lengthening of the nighttime hours, till at the autumnal equinox they were again matched; but the shift continued to Winter solstice when the daytime hours were at their shortest (and the nighttime hours their longest).

Now clearly such a system is geographically linked – as the amount of daytime one gets depends where on the globe one lives (latitude) – so each location could have its own version of unequal hours starting from its own determination of when the day started (depending on longitude). Up here ³ in the U.K. where the the contrast in 'day' length between Summer and Winter is quite stark, we can imagine a mid-summer day having daylight hours twice as long as nighttime hours – and the converse in Winter. Further North, up ³ near Arctic circle, if the convention was ever adopted there, the situation would get even more extreme!

That notion of local time survived long after the fixed-duration (equal) hour was established. Today we have time zones that often encompass vast areas, but once each town made its own determination of high noon when the sun reached its highest point in the sky, which would vary with longitude. This practice changed with the advent of personal timepieces and fast transportation. When it took several days to ride from London to Bristol, with a portable sundial in the pocket, it was of little import that the difference in longitude led to a different local timezone.

But once people could get on a train in one location, with their watch set to the town clock, and get off in another town a few hours later, the importance of a consistent time zone mattered more than the sun being at its highest point at midday wherever you lived in the country.⁴ With easy and quick international travel, the adoption of some kind of agreed global standard also become important. So although today there are different time zones, they are all referenced to Coordinated Universal Time (which aligns with GMT, Greenwich Mean Time). So, even if travel disorientates the body clock, you will know how to reset your watch when you arrive at your destination. If you fly from London to Vancouver you will know that local time is 7 hours displaced from GMT.

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"Twelve hours of sunset, six thousand miles
Illusions and movies, far away smiles
Twelve hours of sunset, half a day in the skies
I'll see you tomorrow as the steel crow flies
Oh, how time flies"

(From the lyrics of 'Twelve hours of sunset' by Roy Harper)

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AM or PM?

So, nowadays, we have 24 hours in a day, and they are all equal  – of the same duration – regardless of the time of year or where we live. But we commonly keep the 2 x 12 labelling, and sometimes we distinguish the two 7 o'clocks as 7 a.m. and 7 p.m. And the same with the two 3 o'clocks and the two 8.15s and the two 11.30s. Which is fine – but I think this runs into trouble when we get to noon.

By noon, I mean what is sometimes called midday as it comes halfway through the 24 day. But I do not think we should call it 12 p.m. I have two reasons to object to this.

One is simply continuity. If we call noon '12 p.m.', then something very odd happens with our hours: we pass from

• …9 a.m. to 10 a.m. to 11 a.m. to 12 p.m. to 1 p.m. to 2 p.m. to 3 p.m….

That surely is bonkers!

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If, instead, we were to call noon '12 a.m.' then we would have a much more sensible progression of hours:

• …9 a.m. to 10 a.m. to 11 a.m. to 12 a.m. to 1 p.m. to 2 p.m. to 3 p.m….

Which seems to work much better. Until we think about minutes – as 12.01 afternoon has a different denotation (p.m.) to 12.00:

• 11.57 a.m. to 11.58 a.m. to 11.59 a.m. to 12.00 a.m. to 12.01 p.m. to 12.02 p.m. to 12.03 p.m….

Perhaps this does not matter? It could be avoided by keeping the a.m. designation till we shift from 12 back to 1:

• 12.57 a.m. to 12.58 a.m. to 12.59 a.m. to 1.00 p.m. to 1.01 p.m. to 1.02 p.m. to 1.03 p.m….

In many ways, that works much better- at least in terms of the flow of numbers and the resetting back to the hour 1. In the UK we have 'British Summer Time' (BST) for half of the year, and during BST (which is an hour ahead of GMT) noon is actually closer to 1 o'clock anyway, so in one sense this would correct for switching to daylight saving time. ⁴

So, if we have to designate noon as a.m. or p.m., I would prefer that system. But clearly whatever is used has to be used by everyone for it to be workable.

And there is another good reason to avoid both of these conventions.

12 a.m. and 12 p.m. should both be midnight

That is, that to call noon either 12 a.m. or 12 p.m. is internally inconsistent (and one thing we do not like in science is inconsistencies: we do not like them when they arise from relating two areas of science, and we really do not like them when they are inherent within a single field).

12. a.m. means 12 ante meridian, that is 12 hours, before noon. And 12 hours before noon is midnight. 12 p.m. means 12 post meridiem, that is 12 hours, after noon. And 12 hours after noon is midnight (the next midnight after the 12 a.m.).

To call noon either 'before noon' (a.m.) or 'after noon' (p.m.) is a crime against good nomenclature. So, I really do not think we should use either 12 a.m. or 12 p.m. to describe 12 noon. (And if 12 p.m. is midnight, is that the midnight at the end of the day, and 12 a.m. the midnight at the start of the day? In which case, is 12 p.m. Thursday the same as 12 a.m. Friday?)

Midnight is equally (that is 12 hours) ante meridiem and post meridiem so even if calling 12 midnight a.m. or p.m. is not strictly self-contradictory, it does not seem especially clear and helpful. So, it seems labelling 12 o'clock, either of the daily 12 o'clocks, with a.m. or p.m. is simply inviting confusion.

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There are two 12s in the day – 12 midnight and 12 noon (or midday). So, we should stick to those terms and use a.m. and p.m. for all the other times that clearly can be seen to reasonably be labelled as before noon or after noon on a particular day.

…9 a.m. to 10 a.m. to 11 a.m. to 12 noon to 1 p.m. to 2 p.m. to 3 p.m…. …9 p.m. to 10 p.m. to 11 p.m. to 12 midnight to 1 a.m. to 2 a.m. to 3 a.m…

I hope we can all agree to that simple convention – or just use the 24 hour clock.

I am pleased that is now sorted. Next we have do away the disruptive twice yearly time-shifts moving to and from so-called daylight saving time and stick to G.M.T. (or even B.S.T. – or any other option as long as we keep to it all year round) – and then I will be a lot happier.

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Notes:

* One could avoid that problem by using different terms or suffixes – but both meanings of 'day' are so well accepted I will avoid distinguishing them as, say, day_solar for the time for a full rotation of the earth compared to the Sun, as from one noon to the next; and day_light for the period between dawn and dusk. Day_solar is also called nycthemeron, but that is not a term I've heard a lot in public discourse.

It actually takes the earth about 23 hours 56' 4" to rotate once on its axis as measured by the distant stars – day_sidereal – but it needs to turn a little more to "catch up with the sun" due to the effect of the Earth's orbit around the Sun.

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¹ I am only too aware that I am writing these words at a time when the people of Gaza have had their electricity supplies stopped as a tactic of the Israeli's state's genocidal war against the Palestinian people, with its declared aim to destroy Hamas. The extensive destruction of Gaza, including the deliberate targeting of journalists, hospitals, refuge camps, ambulances, international aid workers; and the killing and maiming (and orphaning) of many, many thousands of completely innocent children, is supposedly in part justified by acts of terrorism against Israeli people which are just as evil and equally deserving of condemnation. The torturing, raping and murdering of fellow humans is just as despicable and an affront to humanity (and God, for those who believe) regardless of the ethnicity, nationality or religion of the oppressors or victims.

The genocide continues despite the international outcry, including condemnation by many Jewish people from around the world, and, indeed, by many Israeli citizens. Just as the Gazans should not all be treated as guilty of terrorism, neither the Jewish people, nor Israeli citizens, should be collectively identified with the ongoing war crimes of the Israeli state.

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² We commonly use the term 'alternative conception' to imply a wrong idea inconsistent with the canonical conception – a 'misconception'. However two different conceptions of the same target phenomena may both be incorrect, or there may be situations were alternative conceptions are not right or wrong just different. So deciding an hour would be ¹/₁₂ of the night or daytime (and so would change in duration during the year) or be ¹/₂₄ of the whole daily cycle (and so be of constant duration) is a choice of which option is most convenient, clear or practical rather than being right or wrong.

Our labelling of times cannot be 'wrong' as it is a convention, but I think I had an alternative conception of 12 p.m. as I have always assumed that must mean midnight. Perhaps I was taught differently as a child, but just rejected the idea that anyone would think to designate noon as 12 p.m. as just too illogical and unlikely.

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³ 'Up' given the convention that North comes at the top of the map, which is completely arbitrary. If we assume visitors from outside this solar system would chart earth and put the equator half way down their map (another arbitrary choice – William Gilbert's representations of the Earth is his classic 'On the magnet' – arguably the first full length science book – showed the equator vertically), there is a 50:50 chance of which way up they would present the Earth – with Mercator or McArthur.

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⁴ The actual time of high noon varies a little day to day on a system where we have fixed day lengths (rather than days being of slightly different lengths at different times of year) and a fixed 'hour' duration: so solar noon can actually be up to about a quarter of an hour before or after 12.00 GMT (13.00 BST) – even if you live in Greenwich. So, nominal 'midday' is usually not quite exactly midday, even living on the Greenwich meridian. We can either work with a system that matches natural patterns, or one that has consistent fixed points and fixed duration. These days we find the latter option more attractive.

So, to sum up, one could choose to align the clocks with the daily cycle of nature and still define noon as when the sun is seen to be at its zenith (highest point in the sky that day according to an observer in some place), but some days would be slightly shorter and some slightly longer, and your time would not match that of someone living in a town or city to the West or East of your position.

Instead, 12 noon GMT is based on an averaging for when the sun is at its zenith (over Greenwich) that keeps all days as of equal duration and means everyone in the time zone agrees on the time – and someone in another time zone has a different time by a constant and known differential. Well, in principle, anyway.

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