1. Unlike the optical spectrum , the X-ray spectrum is quite simple. 2. In an optical spectrum changbaiite is uniaxial positive and it can be biaxial. 3. Optical dielectric waveguides guide electromagnetic waves in the optical spectrum ( light ). 4. What happens to the EM field when the wave is in the optical spectrum ? 5. In the optical spectrum , the H ? is the only clear emission feature. 6. Only a small part of the optical spectrum is visible to the unaided eye. 7. NGC 5128 appears in the optical spectrum as a fairly large elliptical galaxy with a prominent dust lane. 8. Optical spectrum analyzers also exist, which use direct optical techniques such as a monochromator to make measurements.9. It was identified as such in 1942, when Rudolf Minkowski found that its optical spectrum was extremely unusual. 10. The lines were originally observed as dark features ( absorption lines ) in the optical spectrum of the Sun.