Muggles' Guide to Harry Potter/Magic/Apparition
|Muggles' Guide to Harry Potter - Magic|
|Features||Effectively instantaneous transportation|
|First Appearance||Harry Potter and the Chamber of Secrets|
To Apparate is to transport oneself from one place to another by dissapparating and reapparating, coined from the Latin 'appareo', meaning to appear. Note that while the spelling apparation would seem to be more appropriate for this action, it is almost always spelled apparition in the books; we have retained this possibly somewhat illogical usage.
Extended Description 
In order for a witch or wizard to be allowed to apparate they must first pass a test. One cannot take the test until they are 17 years old. Apparition is very difficult and very dangerous: it is possible for a person to leave parts of their body behind (becoming splinched), which results in usually serious and sometimes fatal damage as a significant piece of them may become detached.
Note that in some editions of some books, this is spelled Apparation; however, the infinitive form, "to apparate," is always spelled the same way. The term disapparate is often used to indicate the first part of the process, so for instance on finding a prisoner has escaped, one might more properly say that he "disapparated" rather than that he "apparated".
The noise of someone disapparating can be rather loud; it is described in Harry Potter and the Order of the Phoenix as being quite loud, like a car's backfire. The noise of someone apparating to where you are is described in Harry Potter and the Goblet of Fire as being a faint pop. Interestingly, in Harry Potter and the Goblet of Fire, when Ludo Bagman disapparates from Harry's vicinity, that too is described as a faint "pop".
There are three important things to remember when apparating, called the 3 Ds, which stand for destination, determination and deliberation.
- Step One: Fix your mind firmly upon the desired destination.
- Step Two: Focus your determination to occupy the visualized space. Let your yearning to enter it flood from your mind to every particle of your body.
- Step Three: Turn on the spot, feeling your way into nothingness, moving with deliberation.
Spells local to Hogwarts School prevent apparition within the school grounds, part of the methods used to protect Hogwarts from outsiders. This is mentioned repeatedly by Hermione, who read it in the book Hogwarts: A History.
In order to allow the students to learn apparition, the spells preventing apparition within Hogwarts are locally and temporarily lifted in the Great Hall. We only see this being done in Harry Potter and the Half-Blood Prince, when Harry's year group has the opportunity to learn; however, we can safely assume that every year group in turn has this opportunity.
Apparition is deliberately shown as being similar to Muggle driving, with an age limit, safety concerns, licensing requirements, and a proficiency test. It is, as such, an important rite of passage for a young wizard. The fact that Ron fails his test because of half an eyebrow echoes the type of failure that many readers of this book will experience, or in the case of older readers, will have experienced, at the hands of a Muggle driving examiner.
It is necessary to show that Apparition is not an instantaneous process, that it takes calmness, preparation, and deliberation to perform it; otherwise all Wizardly means of transportation, including brooms, Portkeys, the Knight Bus, and the Floo Network, would pale into insignificance. It is useful to note that Mr. Weasley comments in Harry Potter and the Goblet of Fire that some wizards will not Apparate because of the danger of splinching; they rely instead on their brooms and the Floo network.
It should also be noted that in Harry Potter and the Deathly Hallows, Mad-Eye Moody reports that they can't leave Privet Drive by Disapparating because the Ministry has, for Harry's "protection", banned the use of Apparition, Portkeys, and Floo transport in the vicinity. The implication is that Apparition can be, if not prevented over a relatively wide region, at least detected and traced.
Apparition is also, apparently, range-limited. In Harry Potter and the Deathly Hallows, Voldemort is summoned from Nurmengard to Malfoy Manor. Voldemort is apparently unable to Apparate directly to Malfoy Manor and must fly for some time. This may be merely a plot device, to give the Trio time to escape, but it seems consistent with what we know about Apparition.
As noted, we first see Apparition when Dobby Disapparates from Privet Drive. At the time, this is not named, and we have no understanding of the mechanism involved, or whether it is only house-elves who can do this. Awareness that humans, also, can Apparate is not given to us until Harry's fourth year, when Mr. Weasley is talking to Harry and his own children about Apparition.
- Why is it that Wizards and Witches are not able to disapparate for their own safety when they are faced with danger? For example, when Harry's mother knew that Lord Voldemort would likely try to kill her and Harry (after killing James, her husband) why didn't she just disapparate with Harry (in a side-along fashion, as in Harry Potter and the Half-Blood Prince)? True, many wizarding houses have special spells placed upon them that will not allow for apparition, however, one would think that these could be lifted by the witch or wizard that placed the spell upon the home.
- Why in Harry Potter and the The Goblet of Fire does disapparition sound like a small popping, but in Harry Potter and the Half-Blood Prince it sounds like a gun shot or a car back firing? If apparition really is as loud as a car back fire it would be highly restrictive on when and where you could use it.
- Can muggles side-along apparate with wizards?
- What is it about Apparition that makes it so hard to do?
Greater Picture 
It is interesting that in Harry Potter and the Half-Blood Prince, the two house-elves Dobby and Kreacher are seen to apparate within the school, where in most earlier books Dobby, at least, apparently travels by more ordinary means within the castle. (He does apparate out of Harry's clutches when Harry is in the Hospital Wing, in Harry Potter and the Chamber of Secrets.) J. K. Rowling has stated that house-elf magic is different from human magic, and that they must be able to apparate in order to perform all their duties around the castle; so presumably the anti-apparition spells that block humans from apparating in the castle have been constructed to allow house-elves to continue to apparate. It should be noted that Kreacher apparently reported that he was able to Apparate out of the cave of the locket in Harry Potter and the Deathly Hallows, although he didn't call it that: he said that his Master had summoned him, so he went. The implication is that, even when cast by a master wizard like Voldemort, anti-Apparition spells are of no use against house-elves, or a separate spell must be cast to prevent house-elves from being able to apparate. If in fact a separate spell must be used to prevent House-elf apparition, such a spell was deliberately not performed at Hogwarts since the ability to apparate is necessary to allow them to do their work. As Voldemort is known to "look down upon 'lesser' creatures," it is most likely that he simply would not go to the effort of setting such a spell, as he would consider it a waste of effort to protect against such insignificant creatures. Voldemort's arrogant disregard for these sorts of magic which are outside of human capabilities shows a critical flaw in his character; magic beyond his understanding ultimately leads to his downfall.
Instantaneous transportation by matter transmission has been written about extensively by science fiction writers for years; Larry Niven (Wikipedia link) has done considerable work on the mathematics involved and has reached some interesting conclusions. One issue, when transporting from one place on the surface of the earth to another, is the relative motion; because the earth is rotating, every point on the surface is moving in a different direction. Although it seems contra-intuitive, if you instantaneously transport yourself from Germany to London, keeping the speed of the earth's surface in Germany as you travel, you will find yourself propelled into the ground and towards the west at a speed of several hundred miles an hour as you arrive. This is quite possibly the reason for the limitation on long-distance Apparition, the limitation being the amount of differential velocity you can handle; possibly there are specialists in apparition who are able to apparate longer distances. Whether the author of this series is familiar with Niven's works is unknown.