How did we measure the fastest speed there is? | The History of the Speed of Light Part I

The speed of light is 299,792,458 meters per second. That's an incredibly fast speed. But how did we even figure that out in the first place? And how do we even know it that accurately?

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Here are links to the papers mentioned:

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👩🏽‍💻 Dr Becky Smethurst is an astrophysicist researching galaxies and supermassive black holes at Christ Church at the University of Oxford.

[DrBecky]

Sounds like I had a brain typo at the beginning of this video and mixed up the digits when I quoted the speed of light! It should be 299, 792, 458m/s

Also, we didn’t define the speed of light as 300, 000, 000 m/S because then the dimensions of everything around the world would have changed!

[pimwillemsma]

The fact that Rømer actually drew a face on the sun in his diagram, brings a smile to my face everytime I see it.

[neuvocastezero]

That parallax star field animation is super cool. Also, "The meter is something we humans have invented as just sort of like... a yardstick."
Classic.

[antoniobragancamartins]

Dr Becky, I'm Brazilian man, I'm not a physic and I'm not an astronomer, I'm a telecommunications specialist, but I'm an enthusiast with space, and i want to say you explain in an way that we understand perfectly. Thanks!

[kayinoue]

Your excitement for science and sharing it with others is incredibly endearing and such a joy to see. Thank you for what you do.

[aidanjt]

I love these astrophysics history episodes, they're fantastic.

[theCodyReeder]

I’m going to make my own measurement system in which distance units are defined by how far light travels in one hyperfine transition of a ceasium atom.

[PatricRogers]

My 11yo daughter and I have long shared a love of astronomy, and we enjoy your channel together. She recently started sitting in the front seat of the car with me, and she *asks* me to put on your channel while we drive, instead of playing music on the radio, or music videos. Thank you for being awesome and making such incredible science and the amazing beauty of the complicated real life universe fun and kid-friendly.

[DarkMatterBurrito]

I'm probably crazy, but it seems like using a meter to define the speed of light but then using the speed of light to define the meter is circular reasoning in a way.

[samrodian]

You have just delivered the most entertaining physics lesson I have ever heard! Thank you Dr. Becky.

[AWildBard]

This is the kind of question I've always asked. How do we know what we know? Love this video
Can't say I understand it completely, but I guessed there was a process, and this is a great history / science lesson.

[andrewmullen]

Thanks Dr Becky, for the quote of the century, "the meter is like a yardstick" love it, works on many levels!

[planetyouranus]

When I was just a wee lad, still at school. Many many years ago ( I'm 74 now)
The speed. of light was a given at 186, 000 miles per second.
I haven't yet caught up with metres and kilometres and the like. I doubt I ever will!
But I do enjoy your videos Dr. Becky. You do have a knack for explaining complex scientific matters in the simplest of layman's terms. Which helps an old geezer like me to absorb
some fresh knowledge.
So you see!....You really can teach an old dog new tricks!

[GamByr]

Finally! youtube recommended an excellent channel!
I even clicked the bell

[issamedoot]

Thank you for having this video and this channel. You appeared in my recommendations list and your videos are just amazing. I have learned so much in such a short amount of time! I am currently in university and I became excited when I saw how the equations and math I am learning are being applied in this video. I look forward to seeing more of your videos!

[BenjaminGib]

I’m an editor and fascinated with the speed of light and love the study of it, and I’ve realized that Hell after death is actually editing this video.

[butthurtz]

I love this and could listen to this lady all day long.

[Yora]

That parallax animation is amazing. I didn't expect the effect to be that big.

[Locuts]

I’m amazed that Rømer was able to measure the speed of light as accurately as he was able to given the state of knowledge of the universe in the 17th century. To say nothing of the tools available at the time.

[IVANHOECHAPUT]

I was riveted to my computer screen! Great presentation, but what impressed me most were the outtakes at the end. You are very intelligent, human and adorable!