If you can cast spells as part of your class (you are a Mage, Psychic, or Cleric), then you're also able to naturally detect magic in the area of effect. All spellcasters have this ability. You need only study an area of effect to perceive the aura generated by magic.
Magical auras emanate from magical objects or creatures and mundane objects that are subject to magical effects (such as spells with an ongoing duration, or other permanent enchantments). They also persist in areas subject to magical effects: for example, a room subject to a Circle of Binding may leave a temporary magical residue that's visible to spellcasters, even after the spell ends.
Reading Magical Auras
When you concentrate on a magical aura for a single round, you get a sense of its intensity and type. The intensity of a magical aura is usually an indication of the power of its creator (e.g., "weaker," "stronger" or "equal” in power to you, etc), and its type indicates what sort of magic was used to create it (sorcery, psionics, or thaumaturgy).
In the same way, Psychics can detect sentience (the presence of a thinking mind) within magical auras.
The longer the spellcaster concentrates on the magical aura, the more details about the magic may be revealed (such as the spell’s school of magic, for example). The GM may allow a spell check to ascertain further detail, but such detail may be impossible to discern without using spells expressly designed for this purpose, like Aura Analysis or Magic Distillation.