I was alerted to an animation by this tweet:
If the Moon were only a few hundred km away, it would look AMAZING… but you’d be way too dead to notice.
An animation artist has arted an animation of what it would look like if the moon were about 420km above the earth’s surface. That’s about the same altitude as the International Space Station. And yes, it does look amazing:
Here’s the cool stuff:
If the Moon were that close — 420 km (260 miles) over the surface of the Earth — it would be over 100º in size, literally more than half the sky! Right now it’s a mere 0.5º in size, for comparison.
It’s dark in the middle because with the Moon blocking the Sun for so much of the Earth, there’s no light to reflect and illuminate the Moon there!
The motion in the video is sped up; at that distance the Moon would orbit the Earth in about 90 minutes or so. It would cross the sky in very roughly five minutes.
And here’s the kinda weird bit:
The Earth has about 80 times the mass of the Moon, so if you could situate yourself exactly halfway between them, the Earth would pull on you 80x harder than the Moon. But it’s worse than that; gravity drops as the square of the distance, and the Moon is pretty far away. Right now, the center of the Earth is roughly 6400 km below you, and the Moon’s center is about 380,000 km above you. Take the ratio and square it, and you see that the Earth pulls on you 3500 times harder just because it’s closer. Add in the fact that the Earth is more massive, and you’ll find it pulls on you about 300,000 times harder than the Moon!
That’s why you don’t notice the gravity of the Moon. It’s only 0.0003% as strong as what you feel from the Earth.
But if the moon were 420km away,and you redo the gravity calculation, you’d find the force of gravity from the Moon on you is 1/10th that of Earth!
When the Moon passed overhead, you’d weigh 10% less.
Weight Watchers paradise.
But sadly, that’s where the good news ends. Because tides.
If we bring the Moon in really close, suddenly one side of the Earth is a lot closer to the Moon than the other: The Earth’s near side is 2158 km from the Moon’s center, and the far side is nearly 15,000 km away. That’s a huge difference, and the tides felt by the Earth would be amplified enormously — nearly 100,000 times what we experience now! There would be global floods as a tidal wave kilometers high sweeps around the world every 90 minutes (due to the Moon’s closer, faster orbit), scouring clean everything in its path.
That, and the fact that the earth would be so pulled and stretched that the crust would start to fall apart and the sea would probably boil away as the magma beneath the earth’s surface was exposed.
Oh, and the high likelihood that the moon would be pulled apart by the earth’s gravitational forces.
Look, it’s not going to end well.
In fact, the reason we are still here – and that the moon is still there – is exactly that: that we are here and it is there. Anything else would result in certain disaster. So there’s something to brighten your journey home today.