But this new planet wasn't in our solar system—it was orbiting another star. If you thought it was hard to remember the names of our own planets, try all the planets, with names like HD 189733b. Telescopes have a limited resolving power—the smallest angular size they can “see.” For the Hubble Space Telescope that’s 0.05 arc second, which is incredibly tiny—about 1/72,000 of a degree. Sure, Jupiter is easy to see in our own night sky, because of the sunlight reflecting off its surface. When we’re looking at the light from a star, the planets around it just aren’t bright enough to be discernible.