All your life you have been watching the moon track through its phases. Even if you have not been paying much attention, it’s been there. But because the moon is tidally locked to Earth — meaning it spins on its axis once every orbit around Earth — you have only seen one face of its globe. Every month, it’s the same “man in the moon” dark and light patches. Until the space age began, no one had ever, ever seen the moon’s other face.