Supermoon! Blue moon! Full moon! People do get excited about this, at least if media coverage and social media posts are any indication. Do I? Well, a full moon means I can see to put the garbage out more easily at night time.
A full moon does allow you to see all of the Earth-facing side all at once, and it is an impressive sight.
https://upload.wikimedia.org/wikipedia/commons/thumb/1/10/Supermoon_Nov-14-2016-minneapolis.jpg/220px-Supermoon_Nov-14-2016-minneapolis.jpg
But can you see any depth here, any three-dimensionality? The illumination is as though you shone a lamp—in this case the sun—directly down onto a surface. There are no shadows, no sense of how deep the craters are, or how high the mountains.
By contrast, when the moon is partially illuminated, the shadows along the terminator, the line that separates day and night—they are long and very revealing. Take a look at this
https://i.pinimg.com/originals/14/92/db/1492dba19d1127cd837131be0d8e2a11.jpg
Those craters along the terminator have depth. If you look closely, you may see a light dot in the middle of these dark crater floors. That is a central peak formed when the crater formed. Think of the impact of a meteorite melting the lunar rock, and then that molten rock “freezing” and preserving the shape of that resulting ripple. This slow-motion video of a drop striking water’s surface is a good analogy.
https://thumbs.gfycat.com/DecentGrossDotterel-size_restricted.gif
And this is the result in the lunar crater Tycho.
https://upload.wikimedia.org/wikipedia/commons/thumb/5/55/Tycho_LRO.png/800px-Tycho_LRO.png
If you were standing on the moon when it was full, what would you see of the Earth?
https://griffithobservatory.org/wp-content/uploads/2021/03/moon_panel_left_rightgraphic.jpg
The Earth would be “new”, that is, unilluminated. And standing on the surface of a new moon, you would see a full Earth. Moon phases as seen from the Earth are mirror images of Earth phases as seen from the moon.
When the moon is a very thin sliver of a crescent, the Earth appears to a lunar observer as almost full, almost completely illuminated. The Earth is very bright. It’s bigger than the moon, and much more reflective. Standing in the dark unilluminated part of the moon, you would be flooded with Earthlight.
And that’s what we see during my favorite lunar phase.
https://images.immediate.co.uk/production/volatile/sites/25/2019/02/IMG_7204-35aee7f.jpg
You can see the part of the moon unilluminated by the sun, by the light of…the Earth.
I’ll leave the light of the full moon to the headline writers and werewolves. Give me a three day old lunar phase any day.
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