Asteroids—like planets—don’t emit visible light. Planets, asteroids, and meteoroids are illuminated only by the light they reflect from the Sun. Finding asteroids is more difficult, however, since they are so much smaller and therefore dimmer and harder to see. Comets have bright trailing tails and shooting stars are relatively nearby and bright. Asteroids, on the other hand, have no readily apparent features so discovering them was (and is) a challenge.
