The Gaussian-School of Higher-Arithmetic (1831, updated 2022) ; tutorial #8.
Quantum-Relativity (qr) .
Using the Gaussian School of Higher Arithmetic we can explain everything (see footnote), but first, before we explain everything else, one first needs to understand the subject of Quantum-Relativity (qr). Once one understands Quantum-Relativity, then I guess that most people will no longer even want to know about anything else, but everything else is there for you, if you find that you do still want to know.
Background photo; an hypnotically distorted view of "the Great Jewels of the Pleiades".
(At this trivial magnification, all distant stars should actually be represented by single pixels of light.)