Today’s Wonder of the Day was inspired by D'Juan from AL. D'Juan Wonders, “How fast is the speed of light?” Thanks for WONDERing with us, D'Juan!

Do you know what's really fast? Water! Watch the shower head the next time you get ready to clean up in the morning. When you turn the handle, water shoots out really fast. If you take baths, you may have noticed how water rushes out of the nozzle and begins to fill the tub. It's fun to watch the first waves of water reach the end of the bathtub and splash up along the sides.

Now think about something even faster. What are we talking about? Light, of course! When you flip the light switch, does light act like water? Do you see it shoot out of the light bulb and splash over the walls like a wave? No! Light fills the room everywhere instantaneously. It's super fast!

But exactly how fast is light? You certainly can't measure it with your eyes. As we already mentioned, the flick of a light switch instantaneously fills a room with light. Early scientists had noticed this same phenomenon. In fact, many early scientists thought light didn't travel at a fast speed. Instead, they believed it was either instantaneously present or not.

Over short distances, it's impossible to sense the movement of light with the naked eye. To measure the speed of light, scientists would learn that they needed large distances to work with. In 1676, astronomer Ole Rømer was the first scientist to show that light did move at a finite speed rather than instantaneously. He did this by studying the apparent motion of Jupiter's moon Io, which is hundreds of millions of miles from Earth.

It would be a couple hundred more years before James Clerk Maxwell would hypothesize that light was an electromagnetic wave when developing his theory of electromagnetism. Other scientists, including Albert Einstein, developed many other theories about the nature of light and began to develop more and more precise measurements of its speed.

Today, the speed of light in vacuum, known by the mathematical symbol c, is exactly 299,792,458 meters per second. It is an exact mathematical constant, because the meter was redefined in the International System of Units (SI) in 1983 as the distance traveled by light in a vacuum in 1/299,792,458 of a second.

So how fast is that, exactly? Really, really fast! In terms you might be more familiar with, light travels at about 186,000 miles per second or approximately 671 million miles per hour! If you could travel at the speed of light, you could circle the entire Earth over seven times in one second.

According to Einstein's theory of relativity, the speed of light is the maximum speed at which all energy, matter, and information in the universe can travel. So, is it possible to go faster than the speed of light, as the Enterprise did in Star Trek when it hit “warp speed"? Not according to Einstein, but other modern scientists are still developing hypotheses about conditions that might make “warp speed" possible.

The speed of light is an important constant in the study of physics and other advanced scientific disciplines. It has also given rise to an important measurement in astronomy: the light-year, which is defined as the distance light can travel in one year.

The light Earth receives from the Sun takes about eight minutes and 30 seconds to arrive. The light from the next closest stars in our galaxy takes over four years to reach Earth! Light from the farthest stars in distant galaxies could take billions of years to reach Earth.

Some of the most distant galaxies are billions of light-years away. When scientists see light from these distant galaxies, they're literally seeing history, since what they see today doesn't necessarily resemble what those stars would look like today if you were to land on one!

Wonder What's Next?

Tomorrow’s super-salty Wonder of the Day is one you might just have to SEA to believe!