Mumbai - It is a common belief that the cycle of day and night is the same. But this belief is a notion only because the duration of day and night keep changing and its result can be seen today (December 22) as Thursday will be the shortest day and the longest night. It simply means that the sun will set early today and starlit night will be seen quite early today. It will be a grand occasion for Mumbaikars who may flock the beaches to witness the sunset on Thursday. As per experts, the distance between sun and earth keep changing. The earth perpetually remains leaning towards the sun. The place of sunrise keeps changing every day. On December 22, the sun enters the North region. The sun rays will reach the earth obliquely and they will be direct in the southern region of this planet. It results into early sunset in some parts of the earth and longer night. Soon after this, the sun starts journey towards the North and it means the earth will gradually start leaning towards south while moving in its own orbit. As a result of this planetary movements, the day and night is of the same duration on March 22 and September 22.