What was in the video was pretty well confirmed. Astronomers spend a lot of money building telescopes and a lot of time collecting data with them. There are a whole bunch of tricks for determining distance. Considering the brightness of stars is one way. For "close" objects in the galaxy, we can still use parallax, just like how your two eyes give depth perception. Also we know that the more distant an object, the more its emitted spectrum will be shifted (longer, i.e. redder) in frequency, so that method is used for very distant things.
(I know I'm probably answering a rhetorical question, but whatevs. I like talking about science.)
(I know I'm probably answering a rhetorical question, but whatevs. I like talking about science.)
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