What time is it on Mars? Just as on Earth, the time of day on Mars depends on where you are on the planet. When NASA’s two Mars Exploration Rovers, Spirit and Opportunity, land on the red planet a few days from now, they’ll be able to tell us the time there using a system that is thousands of years old here on Earth: the sundial. You’ll be able to watch these first-ever “MarsDials,” and many more sundials all across our own planet, thanks to a project called EarthDial. If you like, you can even join in by making your own sundial for everyone on the Web to see.