I have an apprentice wizard. What does it look like to other people when they cast a spell? What about if they use channeling to improve their chances? I am specifically looking for answers that draw from official published material. I've got a few of the books and have not been able to find anything. I'm wondering if either, a, I'm blind, or b, there might be something in a book I don't possess.
That depends on the spell, some will be subtle (Sleep, you simply have to touch the target), others will have obvious effects (Magic Missiles). But in the end it's all flavor that has to be agreed between the player and the GM.
Channeling, on the other hand, is quite obvious and will produce flashy (and scary, for the ignorant) effects depending on the spell being channeled and what kind of Wind of Magic is being used. The benefit is that you add your Magic characteristic to the result.
This can manifest itself in countless ways, from minor Poltergeist activity around the affected person, right up to Daemonic possession or spontaneous combustion. (...) The effect is they can actually draw to themselves, focus, and direct a Wind of Magic, focusing and making the energies have a tangible effect upon the environment around them.
For those untrained in Channeling, the energies from the winds will be uncontrollable and could manifest randomly. This applies to most hedge wizards (untrained spellcasters), which lack the formal training of apprentices on that ability.
For one untrained in such matters, it is almost impossible for them not to create supernatural effects around themselves unintentionally.
The effects caused by the Tzeentch's Curse (Chaos Manifestations) are also quite obvious, and even the lowest possible effect could be noticed by peasants ("She is a witch!"):
01-10 Witchery: Within 10 yards (5 squares) of you, milk curdles, wine goes sour, and food spoils.
Considering that most apprentices and hedge wizards will roll a single d10 when spellcasting, they have a 10% chance that whatever spell they cast will automatically fail (by rolling a 1) and they will gain an Insanity point, which could also lead to strange situations depending on your state of mind. A bad spellcasting roll could suddenly mean that your wizard is now under Blasphemous Rage and will probably be executed for blaspheming against the gods ("You heretic!").
Arcane spellcasters have the option to create Protective Circles before spellcasting and reducing that chance from 10% to 1% (by rolling an extra d10, see anydice stats), but that will also create obvious spellcasting effects when doing so. That way, you will have a much lower chance of summoning demons from the chaos spontaneously by accident, but ignorant peasants will surely want to burn you at the stake if you cannot explain what a Licensed Wizard means.