Strange things happen to time when

Strange things happen to time when you travel, because the earth is divided into twenty-four parts, ___ ___ a part. You can have days with more or fewer than twenty-four hours, and weeks with more or fewer than seven days. Your ship goes into ___ ___ time part every day if you make a five-day journey across the Atlantic Ocean. As you go into each part, the time ______ one hour. Traveling west, you set your clock back; traveling east, you let it ahead. Each day of your journey has either twenty-five or twenty-three hours. If you travel by ship across the Pacific, you ______ the International Date Line. This is the point where a new day ______. When you go across the line, you change your calendar one full day, back or ahead.