MuggleNet's "New Clues" Theory Board

[angel]

"We watch the skies for the great tides of evil or change that are sometimes marked there....
Mars, bringer of battle, shines brightly above us, suggesting that the fight must break out again soon. How soon, centaurs may attempt to divine by the burning of certain herbs and leaves, by the observation of fume and flame..." p. 603 US ed.

Firenze also said that wizardkind is living though a brief calm between two wars. That "brief calm" was about 15 years, now that the second war did begin.
In SS already, the centaurs noticed that "mars shines bright", so even back then they knew that the fight must break out soon, and they didn't get involved back then b/c they knew that the "second tide" of evil (Voldemort's rise to power) will happen.

The first "tide", the first war took about twenty years, if I'm not mistaken. Now Firenze didn't really say it, but if he refers to the "brief calm" between two wars, the second war isn't going to be shorter than the time in between, or is it?
If they could see that the second war would end also in the next two years (book 7), wouldn't they be able to see that the second "great tide of evil" will only be short?
To me it seems that they see the next war, as long as the first (at least) and that is why he referd to the time in between (15 years after all) as "brief calm".
But he also said that not even their knowledge, and interpretations are foolproof, as it can take ten years to be sure what they are seeing.

They saw "bright mars" five years ago, in SS, and they were right.
I don't think they see the second war as "brief", if they considered the 15 years in between as "brief".

So, does this mean that the second war might not end in book 7, as it is only 2 years until then?
Why can they see that a new war is coming five years prior, but they can't tell when it ends or how long it will last?

Firenze set himself against the Heavens, against what has been foretold, alongside humans. So that makes me think that at least the centaurs interpreted the signs as Voldemort's rise to power, for indefinete time. They didn't see anything about Harry defeating him there, or V's fall from power sometime soon, but Firenze doesn't accept it, and says even they can read the signs wrong sometimes.

"The signs have been read wrong before now, I hope this is one of them", SS

This all makes me think that it has been foretold (or interpreted by the centaurs at least) that the second war will be at least as long as the first, so that is why they refered to 15 years as "brief", they read that Harry will not win, there will not be an end to the second war anytime soon, etc.

"Have we not read what is to come" "Have the stars not let you in on that secret"
"They must show that V is coming back..Bane thinks Firenze should have let Voldemort kill me..I suppose that's written in the stars as well"
(SS)

So what if it is? The centaurs hope that they are wrong, Firenze said that even their knowledge isn't foolproof. And even the prophecy doesn't say that Harry will vanquish the dark lord, only that he has the power to do so.

But if Harry already knew that he wouldn't succeed, that he would be killed, would he even try to fight?