Oort cloud
- Astronomy a spherical cloud of small rocky and icy bodies postulated to orbit the sun beyond the orbit of Pluto and up to 1.5 light years from the sun, and to act as a reservoir of comets. Its existence was proposed by J.H. Oort.【天文】奥尔特云（假定在离太阳1.5光年外冥王星轨道外面绕太阳转的由小岩粒和冰粒形成的作为彗星库的球形云团; 荷兰天文学家J·H·奥尔特最先假设存在这种云）。