Is it "x-ray" or "X-ray"?

[Probeman]

Is it "x-ray" or "X-ray" or (for Pete's sake) "X-Ray"?   

https://en.wikipedia.org/wiki/Radiation

Why do people sometimes capitalize the "x" in "x-ray"?  If we look at the wiki link above, we see that cosmic, radio, alpha, beta and gamma rays are usually not capitalized.  Even "x-rays" are often not capitalized.  What do you all think?

[Mike Matthews]

My vote goes to "x-ray"

[jrminter]

Because Roentgen named them  "X-rays" in 1896. See https://www.nature.com/articles/053274b0.pdf

[Probeman]

Because Roentgen named them  "X-rays" in 1896. See https://www.nature.com/articles/053274b0.pdf

But that's only because he didn't know what to call them!  The "X" was just a placeholder until we understood better what they were.

Mike: I like "x-ray" too.   

[Nicholas Ritchie]

So shouldn't we just call them Roentgen rays and be done with these silly arguments?

[Probeman]

So shouldn't we just call them Roentgen rays and be done with these silly arguments?

Sure, but then you'd need to utilize a diacritical mark over the letter "o" and leave out the "e" to be precise...