The planet circling 47 UMa is about three times the size of Jupiter and orbits its star once every 1,100 days. That puts it about twice as far from its star as Earth is from the sun. Both of these stars can be seen with the naked eye. What we found was a wobble in the star's position that is due to the gravitational pull of the planet. We know they are there because of the effects that they have on their stars.
Gravity holds a star and a planet together.
It is like two kids holding hands and swinging each other around. So when they swing each other, the little kid swings around the most. But the big kid is swung around a little too. We discovered the planets by seeing that the stars are being swung around a little bit. We can even tell how big the planets are and how far away they are by carefully measuring the small movements of the stars.