Decimal Time Explained - What is Decimal Time?

Time keeps on ticking. It was ticking before Earth existed and it will continue after Earth is gone. The time between "ticks" (we may think of as a Second on our watch) is just something we make up to help us time events.

We live on a planet called "Earth".
It takes exactly "1 Day" for the Earth to rotate on its axis so that a point on the surface is in alignment with the Sun we orbit (travel around).
It takes exactly "1 Earth Year" for Earth to orbit our Sun (also known as "Sol").
There is approximately 365.25 Earth Days in one Year.

How we divide up the day (into Hours, Minutes & Seconds) has no planetary bearing; we can divide it up into whatever periods are most useful to us to go about and refer to our business.

24 hour clock

You are probably aware of the system where a Day is divided up into 24 equal Hours. 12 hours are before Noon, we call these "AM" or "Morning"; the 12 hours are after Noon we call "PM" or "Afternoon". Each hour is divided into 60 equal Minutes. Each Minute is divided into 60 equal Seconds. There are therefore 86,400 seconds in a day.

With the 24 hour clock we write a date and time in Year, Month, Day, Hour, Minute, Second format (also known as "ISO 8601" which was published in 1988 by the International Standard Organisation): 2020-02-05 18:00:00
In the UK dates are often written least significant first followed by time most significant first: 5/2/2020 18:00:00 (5th of Feb 2020 at 1800 hours)
In the USA dates are often written 2/5/2020 (totally messed up!)
ISO 8601 simply defines the most significant (largest) part of the date/time is written first, just like with other numeric forms.

You may be asking why 24 hours in a day in the first place?

Egyptians used to observe a set of 36 stars to measure the passage of time at night. Around 1310 BC duodecimal (base 12) and sexagesimal (base 60) were common counting bases so they changed from a set of 36 stars to 24 stars. They divided the day into two 12 hour parts (day and night), and then divided each into 60 minutes then further divided each into 60 seconds. The numbers 12, and in particular 60, are great in terms of the number of factors they have (1,2,3,4,5,6,10,12,15,20,30,60); 20 minutes is 1/3 of an hour. Today most people count in base 10, and not many people tell the time at night by looking at the stars. Some people will make the point that a decimal hour cannot easily be represented when divided into 3; but why would we want to when we can say 10/15/20/25/40/50/70/80 minutes? (there are more Seconds in a day with Decimal Time)

Decimal Time

With Decimal Time, each Day has 10 equal Hours. The first 5 hours we call "AM" (Ante Meridiem meaning before midday) or "Morning", the later 5 we call "PM" (Post Meridiem meaning after midday) or "Afternoon". Each Hour is divided into 100 equal Minutes. Each Minute is divided into 100 equal Seconds. There is therefore 100,000 seconds in a day.

It is very easy to add and subtract Decimal Times which is why it is commonly used in Accounting and Time Logging systems.

When using Decimal Time we write the Year number followed by a Decimal Day number since the start of the Year: 2020-36.75000
In this case we are 3/4 of the way through Day 36 of the Year 2020.

The current Decimal Time is: Tuesday 2020-62.09299
Format: <yyyy-d.hmmss>
Description: yyyy = Year, d = Day (0-365), h = Hour (0-9), mm = Minute (00-59), ss = Second (00-59)

Typically we don't write the second (just the hour and minute) so we write: Tuesday 2020-62.092

Decimal seconds simply introduces a sixth / seventh... digit.
The following shows the current decimal time accurate to a micro decimal second (μs).

Tuesday 2020-62.09299308430

  • Decimal seconds are more precise
  • Decimal datetime is shorter to write
  • Decimal times can easily be added or subtracted
  • In the modern era people are used to working in Base10; we live in a Metric (decimal) world

Standard business hours would be from 3 to 7 (200 minutes in the morning and 200 minutes in the afternoon).

Benefits of Decimal Time

  • Very easy to add and subtract dates and times
  • A Second is more accurate
  • Decimal seconds are simply extra decimal places to the Day number
  • Year and Day are planetary based (an actual physical thing), the length of a Second is adjusted based on the planet we are referring to / living on.

So why doesn't modern society use Decimal Time?

As with any new "weird" but sensible idea, the majority of people see it as crazy until it is explained to them in simple terms. Some industrial sectors switch over first, then it slowly becomes the norm. People do not like to change without reason or understanding; unless they are in politics, in which case the total opposite must be the better way forward. Decimal Time will become more possible as more people learn and understand it, and are introduced to the concept at an early age; it is the children of today that will ensure that ISO 8601 representation becomes the norm, and then their children's children that use Decimal Time in daily life.

What about Months?

A day is how long it takes for a planet to spin on its axis.

A year is defined by the time it takes a planet to travel around its Sun. The time it takes the Moon to travel around the Earth should be ignored when it comes to our day-to-day calendar.

We used to have 10 months in a year. Two months were added into the centre of the calendar in the Roman era to honour Gaius Julius Caesar and his successor Gaius Octavius (AKA Imperator Caesar Divi filius Augustus).

There are 365.25 days in an Earth year. When talking about our Lunar cycles we should be talking about Moon date/time. When talking about Ocean Leap and Neap tides we should use a combination of Earth and Lunar times. Our calendar should not attempt to roughly line up with our Moon Phases.

Other labels

"Week" is a lifestyle label (5 business days & 2 weekend days)
"Weeks in a year" is "365.25/7"

"Day Name" is kind of useful because lifestyles tend to be Week based.

"Months" and "Seasons" are just other labels to split the 365.25 days into smaller pieces; they have no place in date/time notations.

"Daylight Saving Time (DST)", where some countries change their clocks by 1 hour twice per year, has always been a stupid idea. Moving the working/school/farming day back or forth by 1 or 2 hours is sensible depending on your Latitude, but changing the "time" is a silly idea; fortunately March 2020 is the last time clocks will be put forward 1 hour, countries have the option to put clocks back in October or not.

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