Supposedly, the amount of one mili-Helen beauty is sufficient to launch a ship. This witticism derives from the play ’Doctor Faustus’ by Christopher Marlowe, and it is based on Homer’s depiction of Helen of Troy, who had ’the face that launched a thousand ships.’ Specifically, if Helen was the measure of beauty which launches ships, then one ship could be launched by thousand smaller amounts, i.e. mili-Helen.
This Marlowe’s idea may sound like a nerdy joke plot, but in reality, there is no reason why a measurement scale for the amount of something like ’amount of beauty sufficient to launch a ship’ should not be linked to a unit called Helena. There is no reason as well why it should not be converted into decimals such as deci, centi, and millihelens.
Almost all measurement scales are similarly defined – by an arrangement, or a convention, starting with the way we measure a ’conventional’ unit, such as temperature, to the way we measure something we consider a natural process, which is the passing of time.
Although from the 21st-century point of view, they seem so common, seconds, minutes and hours are only intervals which humans chose to keep time for historical reasons. However, time could have been measured in completely different intervals. In Soviet Russia and during the French Revolution, calendars with a completely different organization of the number of months and days of the week were devised. Additionally, even one day could be divided differently – say, for example, into 10 smerlings, so each smerling counts 10 turdnarks, which could be divided into 100 remlins or perhaps 100 zomogloas.
Instead of these weird names, we use well-known seconds as the basic unit of keeping time. However, if we peek into the definitions of measuring units in the SI system, we see that a second, although a measuring unit we are used to, is not exactly defined in an obvious way.
As the time standard, the second is a time interval lasting 9.192.631.770 periods of the radiation corresponding to the transition between the two hyperfine levels of the fundamental unperturbed ground state of the caesium-133 atom. This awkward definition by which atomic clocks measure the exact time, although precise and based on a natural phenomenon, is accepted as a part of a convention which is upheld by the International Committee for Weights and Measures (CIPM) seated at the Pavillon de Breteuil, near Paris.
However, if we speak about measures within one year, there is a genuine measurement based on a natural phenomenon, and hypothetically, it is not part of a convention. It is an average day length, the time required for the Earth to rotate about its axis, i.e. the time required for the Sun to seemingly make one circuit around the planet.
The so-called sidereal day, the time required for the Earth to rotate once relative to ‘fixed stars’, calculated in the basic unit, lasts 86,164 seconds. When you think about it, this is an inconvenient number, without a deeper meaning whatsoever, and aside from the fact that it is ‘astronomical’, the real day was supposed to align with the tradition of dividing it into 24 parts, which are then divided into 60 minutes, and then into 60 parts to get seconds.
The definition, in addition to it being inconvenient, is inadequate, when taking into account how the day is really defined, how long it lasts, and that atomic clocks annually lose a second, according to the current definition, which needs to be added as a ‘leap’ one, pursuant to an extra convention.
This stems from the fact that things were defined in reverse order – a day is not only more natural but also a much older concept than seconds or hours. In not-so-ancient history, before mechanical clocks, time was actually measured temporally – the length of an hour was adapted so that there were 12 of them between the sunrise and the sunset.
At the time of sundials, a day was already divided into 24 parts, from midnight to midnight. In practice, they were not equal parts, since daytime is longer in summer, and each single hour lasted longer. The 24-part division is an older concept than the term hour, and the word originated from a Greek name for ‘ part of a day.’
By all accounts, such division of a day came from the ancient Sumerians, but actually, the exact reason is not known. There are several hypotheses on the subject. According to one, lunar phases are the reason. If the ancient people observed that 30 days elapsed between two lunar phases, and that there are 12 lunar phases during the year, they could similarly divide daytime into 12, i.e. 24 parts. However, Romans were the ones who strictly defined a year into 12 months, therefore, this explanation is rather flimsy, to say the least.
Another explanation is related to the 12 constellations of the Zodiac, which in a year rotate on the celestial sphere so that they return to the same position. However, if you have ever observed the night sky, you will quickly learn that the choice of constellations was not so ambiguous and that the popularity of the number 12 in ancient Babylon had probably an impact on the number of constellations.
One of the explanations is linked to a human hand which allegedly induced the Sumerians to divide a day into 12 parts. If you flex your thumb and look at the insides of your hand, you notice that each of the four fingers is divided into three parts, so you have 12 equal parts in front of you. This made the counting of hours easier, and the day got to be divided into 12 parts.
This is accompanied by the convenience of the number 24 being divisible by 2, 3, 4, 6, 8 and 12, so it is much easier to calculate with it than with the numbers 10 or 100 when required to divide it into parts. Nevertheless, there are no compelling arguments to accept or reject any of these hypotheses, and it might be that all the stated reasons contributed to a day being divided into 24 hours. Be that as it may, if (when) we meet an extra-terrestrial civilization, the first thing they won’t understand about us is why we count time in twenty-fourths of a planet’s rotation. And we worry so much when they go by so quickly.
S.B.
Photo: Depositphotos/Pietus