That is right. And we can do this at rest wrt the clock and see that the one second remains as one second. Thus the motion of the light has no effect. That is it.
It's called time dilation. You define your time using local motion, and you define your second using the motion of light as you see it. You count 9,192,631,770 microwave peaks going past you, and if that light goes slower your second is bigger. That's the scientific fact.
If we move the clock then there are all sorts of effects to take in account and when we do that we also see that one second remains as one second.
One second remains as one second, but it isn't the same as it was.
And of course the postulate that the speed of light is a constant is needed for special relativity to work and it does -
Experimental Basis of Relativity.
Special relativity works, but don't trust Baez. This is what the Baez website says about the
speed of light. And guess what? It's wrong. You
know it's wrong because the article contradicts itself saying
"This interpretation is perfectly valid and makes good physical sense" then 5 paragraphs later says "
it does not even make any sense to say that it varies." Garbage.
Of course you could postulate that the speed of light is not a constant. In that case you have to state how it varies, e.g. that a specific transformation between coordinates is needed (e.g. the Lorentz transformation). In that case you get the same theory from a more complex set of postulates.
Look at the bottom of page 150 of The Foundation of The general Theory of relativity where Einstein says
"the principle of the constancy of the velocity of light in vacuo must be modified.". Or look at section 22 of Einstein's 1916 book
Relativity: The Special and General Theory, and what you see is this:
"In the second place our result shows that, according to the general theory of relativity, the law of the constancy of the velocity of light in vacuo, which constitutes one of the two fundamental assumptions in the special theory of relativity and to which we have already frequently referred, cannot claim any unlimited validity. A curvature of rays of light can only take place when the velocity of propagation of light varies with position".
That principle, that assumption, was the postulate:
the constancy of the speed of light. Einstein was German, he didn't speak English in 1916 when he wrote this stuff. The word he used wasn't velocity, it was
geschwindigkeit, which means both velocity and speed. There's only the one word in German. This and the context tells us that when he approved the translation, he was talking about
speed, like the Baez article says. He was talking about
speed because even something as simple as a mirror changes the
velocity of a beam of light. This was a popular science book. The word velocity here was employed in the common usage, as in "high velocity bullet". Claiming that he was talking about a vector-quantity velocity reduces this paragraph to a ridiculous tautology. He would have been saying light curves because it changes direction! His meaning is obvious, it’s clear as a crystal bell. Read the original and there it is in black and white from the man himself:
die Ausbreitungsgeschwindigkeit des Lichtes mit dem Orte variiert. Translate it yourself. Find a friend or use google. It's accurate:
http://translate.google.com/#de|en|die Ausbreitungsgeschwindigkeit des Lichtes mit dem Orte variiert
Then you can wish it away and be a troll like KK who dismisses Einstein, and denies the bleeding obvious because it challenges his faith.
That leads so a question for you which I will put into another post.
No problem. Pay attention to what I said earlier about the photon being a form of alternating current. And think about what I said about permittivity and permeability. Think for
yourself, don't just parrot what you've been taught.
Who cares "why" it happens. What science is interested in in modeling how the universe presents itself to us. How it happens is explained by relativity.
I care. And in case you hasn't noticed, this is relativity+, and I'm with Einstein.
Bedtime.