The Moon’s phases change regularly due to its orbit around the Earth and the changing angle of sunlight hitting its surface. Ancient humans observed this predictable cycle to mark time. A new moon to full moon and back takes about 29.5 days, forming the basis of lunar months. People used these phases to create calendars and plan agriculture, festivals, and religious events. Scientific understanding now explains this through the relative positions of the Earth, Moon, and Sun. This knowledge also helps predict eclipses and tides. Hence, observation of celestial patterns using scientific methods influenced early timekeeping and continues to shape our routines.