On September 23, all towns in the northern hemisphere experience

On September 23, all towns in the northern hemisphere experience equal length of day and night. This is because September 23 marks the autumnal equinox, which is one of two days in a year when the tilt of the Earth's axis is neither towards nor away from the sun. This means that the duration of daylight and darkness is almost equal across the entire planet, giving an equal length of day and night in most parts of the world, including the northern hemisphere.