Time interval from Sun rise to Sun set on a given day is called as Dinmaan of that particular day in Indian Vedic Astrology or Jyotish. As the time of sun rise and the time of sun set keeps on changing throughout the year on different days when observed from some particular place on earth due to revolution of earth around the sun in an elliptical orbit and due to inclination of earth's axis (as we know axis of earth is not vertical but its inclined at an angle of nearly 24° with the vertical.