Why a day has only 24 hours?Why shouldn't we make it 48 hours by decreasing number of minutes per hour to 30?What made them choose 60 seconds per minute, 60 minutes per hour,24 hours per day?What is the reason behind choosing this UNIQUE NUMBER?
The numbers 12 and 60 were considered special by the ancient Greeks.
The number 10 is an obvious base for numbers as we have 10 fingers and thumbs.
The number 12 is also related to the human hand. Each finger has three joints. This means that there are 12 finger joints on a hand. So, you can count to 12 on one hand by touching each of the finger joints is turn with the thumb. This is why 12 is common in measurement.
The reason for the 24 hour day is that the ancient Greeks divided the hours of daylight into 12 hours. They also divided the night into 12 hours giving 24 hours in total. People still use the 12 hour clock where a day is 2 times 12 hours.
The number 60 was chosen for angles and minutes and seconds because if has a lot of factors. 60 is divisible by 1, 2, 3, 4, 5, 6, 10, 12, 15, 20 and 30. In particular it is the smallest number divisible by the numbers 1-6. This means that many fractions of 60 are whole numbers which makes it convenient.