Here's a trick question for you: how long does it take sunlight to travel to Earth? Turns out it makes a huge difference if you measure the time it takes to reach Earth from the Sun's surface and the Sun's core.

A little about light-speed

Light is so fast that in most everyday situations you'll never be able to tell that it doesn't reach your eyes instantly — it takes time. When you flip on the lights in your bedroom, the light races out at about 186,000 miles per second. If it can travel that many miles in a single second, you know it only takes a teeny tiny fraction of a second to travel across your room (even if it's a big one!).

Zoom out to astronomical distances and light-speed takes on a little more meaning. In space, we're talking about things that can be extremely far apart — so far that it doesn't really make sense to measure distances in miles anymore. You lose all sense of the gigantic scale of the universe. Instead, we make use of light-speed to find a new cosmic measuring stick: the light-year.

How far does light travel in a year?

You now know that light travels at 186,000 miles per second, so how far does it go in a year? Multiply that number by 60 seconds per minute, times 60 minutes per hour, times 24 hours a day, times 365 days a year ... that's just under 6,000,000,000,000 (6 trillion) miles!

When could it possibly make sense to talk about distances that big?!

Our Sun is pretty close — "only" about 93 million miles away. The next closest star, Proxima Centauri, is about 25,000,000,000,000 (25 trillion) miles, or 4.2 light-years, away though — and that's just the Sun's closest neighbor! We know of things that are way farther away, like a galaxy called MACS0647-JD. That galaxy is about 78,000,000,000,000,000,000,000 miles away! In light-years, that's about 13.3 billion.

But let's zoom back in to our own solar system ...

How long does it take light to reach Earth from the Sun?

Well ... it's complicated. Traveling at 186,000 miles per hour, it takes light about 8 minutes to travel the 93 million miles from the surface of the Sun to Earth. Seems simple enough, right?

Here's the thing ... sunlight doesn't start its journey at the Sun's surface.

Credit: LAPO/Ashley Balzer

Light begins its journey deeper within the fiery furnace, in the Sun's core. Here, atoms are fusing together to form new elements and crazy amounts of energy are released in the process.

But when light is created inside the Sun, it doesn't get to travel on a straight path out. Instead, it gets trapped in the radiative zone for 100,000 years or even longer!

Credit: NASA/Jenny Mottar

It's sometimes called the random walk. Stuff is so densely packed together inside the Sun that light doesn't go far (we're talking less than a centimeter) before smacking into something. It bounces off in a new direction, but then smacks into something else. This happens at random and makes sunlight's journey a very long and chaotic one.

But if it weren't for this process, you probably wouldn't be alive to read this right now!

Sunlight is initially created as gamma rays, which are far more likely to fry you than turn you into a Hulk-like creature. With each collision between particles, the energy is reduced ever so slightly. Fast forward a hundred thousand years or so and we're left with light that tends to be much less harmful to life on Earth (Earth's atmosphere and magnetic field offer further protection from some of the more energetic forms of light that do make it out of the Sun).

So, how long does it take for sunlight to reach the Earth? About 8 minutes ... or 100,000 years or more!