This question is brought up due to confusion over that cool video of an asteroid cricling the Earth and not understanding the explanation of what the L1 represents. Thank you.
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So, when two bodies are orbiting each other (like earth orbiting the sun), it turns out there are five places where their mutual gravity and orbits mean that an object can stay in the same place relative both of them. These places are called “legrange points”
L1 – the first Legrange point – is the place in between them where their gravity is equal. The easiest way to imagine this is to imagine a really big trampoline, and two people sitting on it. If you look at the trampoline between the two people, there’s going to be a point at which the trampoline is flat – it’s going to be closer to the lighter person; but there’s going to be that flat point.
Basically, if a light object (compared to Earth) is sitting at L1 it will have the same orbit time as the Earth as it tries to orbit the Sun and Earth at the same time, can’t figure out which one to orbit, and so stays right in between them.
However, it’s an “unstable” point, meaning that if the object moves just a little, it will orbit faster or slower and tend to end up orbiting one body or the other. You can solve this with a spacecraft using power to stay in that location – the James Webb Space Telescope is at L2 (a point past Earth in a direct line with the sun, which is also unstable; but has the advantage of being mostly hidden from the Sun by Earth), because it will mostly stay in place.
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