Visible light

• What Is the Difference Between Paraxial and Marginal Rays?
  Paraxial rays lie near an optical axis at small angles; marginal rays pass through the aperture edge and may reveal lens aberrations.
• Why Do Nearby Objects Look Faster from a Moving Train?
  Nearby objects seem to race past a train because their direction changes faster across your field of view than the direction of distant objects.
• If Atoms Are Mostly Empty Space, Why Doesn’t Light Pass Through Everything?
  Atoms are not hard little obstacles, but their electrons interact with light. A material’s structure and energy levels determine whether it transmits, absorbs.
• Can a Monochromatic Pulse Exist?
  A strictly monochromatic wave cannot be a finite pulse: localization in time requires a range of frequencies, though that range can be very narrow.
• How Are Electromagnetic Radiation and Blackbody Radiation Related?
  Blackbody radiation is the electromagnetic spectrum emitted by an ideal absorber; temperature sets its shape, while Planck’s law and Wien’s law quantify it.
• Can Light and Darkness Coexist?
  Light and darkness can appear together as illumination varies across a scene; darkness is low or absent visible light, not a separate substance.
• Can You See a Rainbow on the Moon or Other Worlds?
  A lunar surface has no ordinary rainbow because it lacks rain and a substantial atmosphere. Learn what a rainbow needs and where one might occur elsewhere.