The dark side of the Moon

Ask a friend to sit in a chair as the Earth. (Ideally they should be spinning on a swivel chair, but let's keep this simple). Stand facing them. You are the Moon. Now stay facing them, but shuffle off sideways in an orbit round them. Face them all the time. Make a complete circuit.

Now you have orbited - but have you rotated? Well, yes you have. You have faced - in turn - every wall in the room. You could only do that by rotating. You didn't spin on the spot, but you did turn.

Incidentally, if your face is lit up by a bright window as you orbit, your partner will see the changing phases of the Moon, as you are first lit full-face (full Moon) then part-lit (waxing and waning) and finally not lit at all (new Moon). But notice that the back of your head is not i darkness all the time. The "dark side" of the Moon isn't always dark!

Day and night Finally, understand more about day and night by experiencing Mount Nose. Face a bright window. Now your head is the Earth. Your nose is a mountain. For a person on Mount Nose, where is the Sun in the sky? Straight overhead, in the middle of their day. Now turn left, and stop when your right ear faces the Sun. Where would the Sun be now? And what would the time be? For the person on Mount Nose, the Sun would be low on the horizon as the Earth turns towards night.

Turn your back to the Sun. Where is the Sun now, and what is the time on Mount Nose? Midnight. One more move to the left and the Sun is rising on Mount Nose. The last quarter turn brings you back to midday.

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