Few sights in the night sky are more eye-catching than a conjunction between the Moon and Venus. And we get to enjoy such a meeting both tonight and tomorrow night. Venus is the brilliant “evening star.” It’s well above the Moon this evening, but much closer to it tomorrow night.

We’ve explored both worlds in detail. But more missions are being planned – especially to the Moon. Some day, swarms of people and machines might be on the surface or in orbit. Scientists are thinking about ways to time all that activity. So they’re trying to develop a new timekeeping system for the Moon.

You might think that a lunar version of GPS might do the trick. And it could. But time passes at different rates for objects on the surface and in orbit. And neither of those rates matches the passage of time on Earth.

That’s all because of relativity. Clocks in orbit tick a little slower because they’re moving faster than those on the ground. But they tick faster because they don’t feel as strong a gravitational pull. If GPS didn’t account for those effects on Earth, the whole system would become worthless in a few days.

But you can’t use the same numbers at the Moon. The Moon’s gravity is weaker than Earth’s, and orbiting satellites move more slowly. Clocks also have to account for the fact that the Moon is orbiting Earth.

So scientists are working out the details of lunar clocks – perhaps leading to a GPS system for our satellite world.

Script by Damond Benningfield