Rømer and the moons of Jupiter
In 1676 the Danish astronomer Ole Rømer noticed that eclipses of Jupiter's moon Io were delayed when the Earth was farther from Jupiter. Light, then, takes time to reach us. His measurements gave roughly the right order of magnitude for its speed, around 220,000 km/s.
Light in glass
In an optical fibre light travels about a third slower than in a vacuum, roughly 200 kilometres per millisecond. From Bratislava to New York it's about 6,800 km as the crow flies, so the round trip takes at least around 70 ms. The real ping tends to be higher, because cables don't run in a straight line and every router adds a little time.
Why the server's distance matters
In games like Counter-Strike milliseconds decide. That's why players from Slovakia play on servers in, say, Frankfurt or Vienna, and Cloudflare has servers in hundreds of cities so that content is as close to you as possible.
Satellites: high versus low
Classic satellite internet uses satellites at an altitude of 35,786 km. The signal has to travel up and down twice, so the ping never drops below about 480 ms, and in practice it's even higher. Starlink flies at an altitude of only around 550 km, so its ping is similar to a terrestrial connection, usually 25 to 60 ms. Stock traders between Chicago and New York even use microwave links, because a signal travels faster through air than through glass.