Human, the world does not conform to you. You probably already know this; sure, time is an illusion.
Everyone knows what a day is. The concept exists in every language and culture that we know of throughout history. And yet, if you scratch the surface and start asking questions, days becomes surprisingly hard to pin down. Eventually, you'd discover that there's more than one definition, and that the one we base our clocks on is actually pretty surprising, with fascinating consequences.
This is the first in a series on blog posts in which I'll be writing on our basis for timekeeping, in more depth than you probably wanted, through the lens of one of its most beautiful consequences. There's a lot to unpack here — touching on astronomy, geometry, physics, a bit of philosophy, maybe some photography, and while programming isn't strictly necessary, there will be a fair amount of that too.
I've given your subconscious a bit of time to play with precisely defining a day, and hopefully an idea or two has begun to take shape in the back of your mind. There are a few likely candidates