终切 meaning in English

egress

Even with the much closer venus , the observations were tricky ; it was crucial to know the exact geographic positions of the observing stations and to accurately time the four “ contacts ” between venus and the sun . ( the first and second contacts occur at ingress , when venus ' s disk touches the sun ' s from first the outside and then the inside ; the third and fourth contacts occur at egress . ) but the potential payoff from the observations would be enormous
即使是距离近得多的金星，这个测量也不容易；必须要知道观测站确实的地理位置，且要能准确测定凌日时金星和太阳发生四次接触的时间（第一和第二次接触发生在初切，即金星的盘面由外然后再内接触到太阳盘面；第三和第四次接触发生于终切）。