Amateur

Deep-sky or Nebula filters can transform a washed-out city skyscape into reasonably dark location. These high-tech wonders are a huge help for backyard astronomers. One look at the Veil Nebula or Barnard’s Loop and you will be hooked. Most light pollution comes from mercury and sodium streetlamps, which radiate blue and yellow light that shows up as bright background sky glow. But many nebulae comprise hydrogen and oxygen atoms that emit green and red light. Light-pollution filters work by blocking the bad stuff in the blue and yellow, and letting through the good stuff in the red and green....

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