Astronomy Fundamentals

Matter and Energy

Does light ever change speed?

Yes, light can change speed and direction when it goes through different materials. All materials that transmit light have a property called index of refraction. The index of refraction is 1 for a perfect vacuum, 1.0003 for air, 1.33 for water, about 1.5 for various kinds of glass, and 2.42 for diamond. Light travels more slowly through higher index-of-refraction materials than through lower ones.


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