Process of Science: Your friend hypothesizes that the phases of the Moon are produced by Earth's shadow being cast on the Moon's surface. Devise an experiment to prove your friend wrong

Question

Describe an observation you will make (time of day/night, location in sky) and describe what you will see that will clearly demonstrate that your friend's idea cannot be correct.

Answer 1

If you observe any time when the Moon and Sun are both in the sky (e.g., in the daytime during a crescent Moon), you can clearly see that Earth's shadow cannot be cast on the Moon, as it is on the other side of Earth, where the Moon is not. Similarly, an observation of the full Moon shows the opposite: no Earth shadow at all, though the alignment would favor one. If the full Moon occurred when Earth's shadow could not hit it, it should be seen in the daytime, not at night—and then it would have no light source.