我们知道,光源是指能自行发光的物体.因此要判断一个物体是不是光源,要看它是否满足两个条件:首先必须为发光体;其次光是从它自身发出.据此很容易知道,象熄灭的电灯,没点燃的蜡烛,正在放电影时的银幕,月亮,行星(水星、金星、地球、火星、木星、土星、天王星、海王星、冥王星),它们不发光或自身 We know that light sources are self-illuminating objects. Therefore, to determine whether an object is a light source, it depends on whether it satisfies two conditions: first it must be a light body; second light is emitted from itself. It is easy to know accordingly. Like extinguished lights, unlit candles, movies, moons, planets (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto), they don’t shine or