Emission and reflection nebulae differ primarily in their interactions with light, particularly regarding how they emit or reflect light.
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Emission Nebulae: These glow brightly because they are made up of ionized gas that emits light of various colors; this occurs when the gas is energized by nearby young, hot stars.
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Reflection Nebulae: These do not emit their own light but instead reflect the light of nearby stars, typically appearing bluish due to the scattering of shorter wavelength light.
Thus, the correct response is interactions with light.