How does a centaur know what is hidden in Hogwarts?

Question

In Harry Potter and the Sorcerer's Stone, when Harry, Ron, and Malfoy got detention from Professor McGonagall they have to go into the Forbidden Forest with Hagrid to find a unicorn who is injured, badly.

In the Forbidden Forest Harry encounters Voldemort for the first time after his parents died. This information is passed by Firenze, a centaur, who gives Harry some hints by asking questions like what is hidden in Hogwarts right now, and who wants to gain power by using it? So Harry will able to connect recent events with Voldemort.

That means the centaurs already know about the Sorcerer's Stone and that it is hidden in Hogwarts and he also knows that the creature who attacked Harry in the woods is none other than Voldemort.

But how did a centaur know this? The the Sorcerer's Stone is hidden in Hogwarts, and only some teachers, Hagrid, and Dumbledore know about it.

In the books, it is mentioned that centaurs are magical creatures who had a keen interest in astrology. Does their ability to read the stars and planets give them information about secret things or did Hagrid mention this to a centaur or something else?

Answer 1

It’s possible that Hagrid let it slip when talking to them.

We know that Hagrid goes into the Forbidden Forest and sometimes talks to the centaurs. We also know that Hagrid had a hard time keeping information about the Philosopher’s Stone a secret.

“Oh, a fair few … Keep themselves to themselves mostly, but they’re good enough about turnin’ up if ever I want a word. They’re deep, mind, centaurs … they know things … jus’ don’ let on much.”
_{^{- Harry Potter and the Philosopher's Stone, Chapter 15 (The Forbidden Forest)}}

It seems possible that Hagrid could have told them that the Philosopher’s Stone was in Hogwarts. He accidentally gave Harry enough information to figure it out, and Harry was an inexperienced eleven year old who’d just learned about the wizarding world.

It seems unlikely that they divined it - centaur divination is broad.

While it’s possible that the centaurs divined the Philosopher’s Stone being in Hogwarts, from what we know of centaurs’ divination, it tends to be broader and not really focused on details.

“Sybill Trelawney may have Seen, I do not know,’ continued Firenze, and Harry heard the swishing of his tail again as he walked up and down before them, ‘but she wastes her time, in the main, on the self-flattering nonsense humans call fortune-telling. I, however, am here to explain the wisdom of centaurs, which is impersonal and impartial. We watch the skies for the great tides of evil or change that are sometimes marked there. It may take ten years to be sure of what we are seeing.”
_{^{- Harry Potter and the Order of the Phoenix, Chapter 27 (The Centaur and the Sneak)}}

From this, it seems like they wouldn’t get that level of details from the stars. It also seems like divining things can take time, so they probably wouldn’t find out what’s happening as it happens. When we hear one of Firenze’s predictions, it’s very broad, and doesn’t give specific details on anything.

“In the past decade, the indications have been that wizardkind is living through nothing more than a brief calm between two wars. Mars, bringer of battle, shines brightly above us, suggesting that the fight must soon break out again. How soon, centaurs may attempt to divine by the burning of certain herbs and leaves, by the observation of fume and flame …”
_{^{- Harry Potter and the Order of the Phoenix, Chapter 27 (The Centaur and the Sneak)}}

Ron described the lesson as nothing very definitive, and low on details.

“He’s not very definite on anything, is he?’ said Ron in a low voice, as they put out their mallowsweet fire. ‘I mean, I could do with a few more details about this war we’re about to have, couldn’t you?”
_{^{- Harry Potter and the Order of the Phoenix, Chapter 27 (The Centaur and the Sneak)}}

It doesn’t seem like they’d be able to divine the presence of the Philosopher’s Stone.

Answer 2

What Firenze says in Harry Potter and the Order of the Phoenix indicates that the centaurs mostly just get the broad sweep of things:

‘I know that you have learned the names of the planets and their moons in Astronomy,' said Firenze’s calm voice, ‘and that you have mapped the stars' progress through the heavens. Centaurs have unravelled the mysteries of these movements over centuries. Our findings teach us that the future may be glimpsed in the sky above us –'

‘Professor Trelawney did astrology with us!' said Parvati excitedly, raising her hand in front of her so that it stuck up in the air as she lay on her back. ‘Mars causes accidents and burns and things like that, and when it makes an angle to Saturn, like now –' she drew a right-angle in the air above her ‘– that means people need to be extra careful when handling hot things –'

‘That,' said Firenze calmly, ‘is human nonsense.'

Parvati’s hand fell limply to her side.

‘Trivial hurts, tiny human accidents,' said Firenze, as his hooves thudded over the mossy floor. ‘These are of no more significance than the scurryings of ants to the wide universe, and are unaffected by planetary movements.'

‘Professor Trelawney –' began Parvati, in a hurt and indignant voice.

‘– is a human,' said Firenze simply. ‘And is therefore blinkered and fettered by the limitations of your kind.'

Harry turned his head very slightly to look at Parvati. She looked very offended, as did several of the people surrounding her.

‘Sybill Trelawney may have Seen, I do not know,' continued Firenze, and Harry heard the swishing of his tail again as he walked up and down before them, ‘but she wastes her time, in the main, on the self-flattering nonsense humans call fortune-telling. I, however, am here to explain the wisdom of centaurs, which is impersonal and impartial. We watch the skies for the great tides of evil or change that are sometimes marked there. It may take ten years to be sure of what we are seeing.'

Firenze pointed to the red star directly above Harry.

‘In the past decade, the indications have been that wizardkind is living through nothing more than a brief calm between two wars. Mars, bringer of battle, shines brightly above us, suggesting that the fight must soon break out again. How soon, centaurs may attempt to divine by the burning of certain herbs and leaves, by the observation of fume and flame.'

However, he did not give a quantitative picture of how important a particular piece of information needs to be in order that the centaurs get discern it, given a sufficient amount of time. As the last quoted paragraph indicates, even if the motions of the heavenly bodies does not provide sufficiently detailed information, there are other forms of divination that may be used to obtain more in-depth knowledge.

So it seems entirely plausible that the centaurs could have learned about the hiding place of the Philosopher's Stone from divination magic.