But just as biologists can fairly claim to know all the major types of, say, land mammals, astronomers are on the verge of identifying all the major classes of light-emitting objects.

• 但就像生物学家所宣称，他们能够认识陆生哺乳动物所有的主要类别，天文学家也几乎可以辨识发光天体的所有主要类型。