English: NASA's Nuclear Spectroscopic Telescope Array, or NuSTAR, has a complex set of mirrors, or optics, that will help it see high-energy X-ray light in greater detail than ever before. These images show different views of one of two optic units onboard NuSTAR, each consisting of 133 nested cylindrical mirror shells as thin as a fingernail. The mirrors are arranged in this way in order to focus as much X-ray light as possible. X-rays don't behave like visible light. Instead of easily bouncing off surfaces, they tend to be absorbed. However, if an incoming X-ray grazes a surface at a very small, glancing angle, it will be reflected. By nesting mirrors of different sizes and angles, more X-rays can be reflected and focused onto the same spot.