How many seconds does sunlight take to reach Earth?

How to get close to this number

This is a pure division problem, and both inputs are ones you probably already have. Take the distance to the Sun, take the speed of light, divide. Almost nobody does this, because "how long does sunlight take" sounds like a fact to be recalled rather than a calculation to be performed — but the calculation is more reliable than the memory, and it is the habit worth building.

The framing that makes it stick is that you are always looking at the past. Everything you see is delayed by the travel time of light; it is imperceptible across a room and it is eight minutes across the solar system. If the Sun were somehow switched off, the sky would stay bright for that long — the delay is not an abstraction, it is the actual age of the image reaching your eye.

The second half of the explanation is the genuinely startling part and worth separating out. Light escaping the surface takes minutes to reach us, but the energy took an enormously long time to get from the core to the surface in the first place, scattering constantly through dense plasma. The photon leaving the Sun today carries energy released long before human history, which is a different and much larger number hiding behind an ordinary-looking one.