So Dumbledore kept Trelawney around because she gave the prophesy and he didn't want her falling into Voldemorts hands so he couldn't hear all if it, and possibly future ones.

In OotP he keeps her in the castle even once fired.

What happened to her in DH?

We see her in the Battle of Hogwarts throwing crystal balls. Did Voldemort mind rape her? Did he get the prophesy? We know he can break any form mental block like he did on that witch in GoF.

 

Do we know for a fact that she stayed back at Hogwarts for that entire year? She might have gone into hiding with McGonagall's help and returned just for the final battle.

 

I'd guess that Voldemort didn't go to Hogwarts much aside from the time he went to rob Dumbledore's grave. That being said I don't think the Carrows were really in the know so they probably didn't even know about Trelawney and Snape sure as hell wasn't about to say anything. He might have even mentioned to Voldemort that she had left. I'd guess she probably spent most of her time in her tower not bothering with anyone just as she did in the last six books.
I might also add that Voldemort saw the prophecy smash in book 5 so he may very well have given up on trying to find it in the end. He just knew he had to kill Harry.

 

Does anyone have an idea how long Dumbledore was a Transfiguration professor?

 

TL;DR: We don't really know for certain, but the minimum is around twenty years while the maximum is over fifty.

We don't know exactly when Dumbledore began teaching Transfiguration at Hogwarts. The very latest would be in 1938, when he visited Tom Riddle in his orphanage. Dumbledore graduated from Hogwarts in 1899, so he could have began anytime between 1900 - 1938.

It should be taken into consideration that Dumbledore probably did not begin teaching right away - since Dippet was headmaster during this time, and he rejected Tom Riddle the first time he asked for the DADA job for being too young. But then again, this is Dumbledore we're talking about, so anything could be possible.

Anyways, we know that Dumbledore was Headmaster by the time Voldemort visited him and asked for the DADA position. Dumbledore tells us that this event happened ten years after Voldemort's murder of Hepzibah Smith. According the hp-lexicon, the murder happened in 1946. So, by adding the dates, we know that Dumbledore was headmaster by around 1956.

It is also to be noted that during the conversation, Voldemort suggests that Dumbledore recently became Headmaster.

So, Dumbledore was Headmaster Transfiguration Professor from 1900-1938 to 1956 (approximately).

 

Source.

Tom Riddle finishes his 7th year at Hogwarts in 1945, so Dumbledore must have remained teaching until at least then.

 

Do we know if Snape actually created the spells written in the half-blood prince book, or is it just an interpretation/fanon? Could he have just written them down from somewhere else?

 

HP Lexicon on Sectumsempra:

Levicorpus:

 

Palindrome much obliged.

 

I meant "Transfiguration Professor" not "Headmaster" in the last sentence. Corrected. Thanks for the catch!

 

What is the benefit of using a Portkey over apparating? Do Porkeys allow for longer distances?

 

It seems to me that portkeys where used when more than two people where going from place to place. Also Dumbledore used a portkey for Harry in the Mom because he didn't have to side along Harry back to Hogwarts.

 

More people can use the same one. It doesn't require anyone along for the ride to know where they're going, IIRC.

 

Portkeys can transport more than two people, for one thing.

 

But can't apparition do that too? In the DH, we've seen an instance where four people side-apparated together (Harry, Ron, Hermione, and Yaxley), and there isn't any indication anywhere that there's a limit to how many people can side-apparate at once.

 

As far as we can see, there's no real risk to using a Portkey, whereas Apparation can lead to serious injury if done badly.

 

I always assumed that Arthur was talking about underage witches and wizards who couldn't apparate.