The 1970s weren't just the dark ages of paisley and bell-bottoms. Some people were trying to rise above their tragic circumstances - and go to space. And they wanted to use a quirk of physics to help them live there.

Right now we're looking to the moon or to Mars to set up a settlement, but it wasn't always so. Forty years ago, a group called the L5 Society was looking for something a little less substantial to set up camp on. The "L" in L5 refers to a Lagrange Point, or Lagrangian Point, which in turn gets its name from Joseph-Louis Lagrange. He realized that in any two-body system, like the moon orbiting the Earth, or the Earth orbiting the sun, there are points of equilibrium. These points take into account three forces.

The first force is the pull of gravity from the central body. In this case, it would be the Earth, tugging at whatever is near it. The second force is still gravity, but the gravity of the orbiting object. Plunk an object down between the moon and the Earth at just the right point, and the two gravitational pulls will balance out. If the two bodies were stationary, that would be that.

But the Earth and moon aren't stationary. They move, and that brings into account centrifugal force, which arises solely due to the motion of the objects. It's the difference between being connected to by a string to a parked car and being connected by a string to a car doing donuts. The car may turn and change direction, but your body will attempt to keep going in the same direction as before. You'll feel something like an outward tug, away from the car. It's the same tug that flattens you against the outside wall of a moving vehicle as it goes around the corner. As the Earth and moon move, objects around them feel the same tug, and that shifts the points of equilibrium slightly. The Lagrangian Points are were all the forces cancel out, and the object will travel along with the two bodies using no power of its own.

It's easy to imagine the Lagrange Point between the Earth and the moon, but there's more than just one point of equilibrium in a two body system. There's also one Lagrange Point to the far side of the Earth, away from the moon. And there's one to the far side of the moon, away from the Earth. These three are Lagrange Points are called L1, L2, and L3. Although you can balance something there, it's hard to do. If the objects shifts slightly further away or closer, it will fall out of equilibrium and needs to correct it course.