When we celebrate the passing of “a year,” what is really being measured is how long it’s taken the Earth to make a full rotation around the sun. Four seasons have passed and we increase the year’s date by one. – Happy New Year!
The reason why so many people consider January 1st to be the start of the New Year is simply because that was the date chosen when the Gregorian calendar was adopted in 1582, and the Gregorian calendar and its January 1st New Year stuck with many people! A different date could have been chosen, and then we’d be wearing party hats and proclaiming “Happy New Year” every year on March 12 or July 29 or November 7 or any other random date!
Throughout history, people all around the world have followed a variety of calendar systems with different dates for the new year, such as the spring or fall equinox or the winter solstice. In some places, calendars other than the Gregorian calendar are still used and different new year dates are still followed!