The convention of designating the middle of the day as "noon" and the middle of the night as "midnight" starting at 12 instead of 1 has historical roots and is primarily based on practical and cultural considerations.
The system of dividing the day into 24 hours has been used for thousands of years and can be traced back to ancient civilizations. The Babylonians, who were among the earliest civilization known to use a base-60 numeral system, divided the day and night into 12 equal parts each. The numbering system they used had a base of 60, which is divisible by many factors, making calculations easier for them. The adoption of a 12-hour system was also influenced by the ancient Egyptians and Greeks.
When mechanical clocks were introduced in medieval Europe, they initially followed the same 12-hour system. These clocks had only one hand, which made it difficult to distinguish between the hours of day and night. To overcome this ambiguity, the clock faces were marked with two sets of numerals: 1 to 12 for the daytime hours and another set from 1 to 12 for the nighttime hours. The numbering for the nighttime hours started from 12, and that convention carried over to the modern clock faces we use today.
Regarding the specific question of why noon and midnight start at 12 instead of 1, it is largely a matter of convention and practicality. Since noon is defined as the time when the sun is at its highest point in the sky, it was natural to assign it to the middle of the day. Similarly, midnight, being the midpoint of the night, was designated as the beginning of a new day.
By starting the numbering at 12, it ensured that the hour preceding noon would be 11, maintaining consistency with the 12-hour clock system and making it easier for people to understand and use. Shifting the starting point to 1 would have required adjusting the entire system of timekeeping, which would have been more complex and less intuitive.
In summary, the convention of starting noon and midnight at 12 instead of 1 has its roots in ancient civilizations and the historical development of timekeeping systems. It has been maintained for practical and cultural reasons, ensuring consistency and ease of use in timekeeping.