Have you ever seen a picture of a comet or asteroid in the sky against a background of stars? Here let me show you. Can you spot the asteroid? Okay I confess there is no asteroid in the image above, but if there was you’d believe me because an asteroid in this image would be indistinguishable from the stars.  They are all points of light, so how can you tell them apart? There’s something that separates asteroids, comets, planets, and all other solar system objects from background stars in an image. When you’re driving in a car and you look to the...