eli5: why are the orbits of celestial bodies elliptical?
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Ellipse is just one possibility of an orbit, it can actually be any conic section (only approximately in reality)
The question why is hard to answer without some arithmetic, but I’m going to try to simplify as best I can.
Imagine being in space around a bigger body and moving with respect to that body. It will draw you to itself bc of gravity. That means your path will be slightly bent by that force. After a while, you moved a bit on that bent trajectory and the planet will be somewhere else from your POV (I don’t know how to better put it. When you pass a car, before you have to look forward to see that car, after you will have to look back). That means the direction of gravity will also have changed from your perspective, curving your path even further. In the end and absent any disturbances, you will arrive at the starting point with the same speed and then make another round.
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