宇宙速度yǔzhòu sùdù物体能够克服地心引力的作用离开地球进入星际空间的速度。宇宙速度分为三级,即第一宇宙速度、第二宇宙速度、第三宇宙速度。{cosmic velocity; velocity at which an object can leave the earth and enter the outer space by overcoming the effect of the terrestrial gravity. The cosmic velocity is classified into three grades: first cosmic velocity or circular velocity; second cosmic velocity or earth escape velocity; and third cosmic velocity or solar escape velocity.}