by Juan Ivaldi, volunteer amateur astronomer at the NPFO

 

We take light for granted, yet it is one of the most important vehicles for getting information about the world around us and the Universe beyond.  The way light works is among the strangest and most wonderful of physical phenomena.  Imagine a particle that has no mass, which undisturbed can travel several billion trillion miles without anyone pushing it, moves in straight lines, and goes so fast that nothing can catch up to it without disintegrating.  The particle just described is a photon.  As a more formal definition, a photon is an elementary particle that acts as the carrier of electromagnetic radiation.  The visible light we see and the invisible light such as ultraviolet, infrared, X-rays and radio are all different wavelengths of light in the electromagnetic spectrum carried by photons. 

 

Like other elementary particles, photons can behave like waves or like particles.  Photons behave like waves when they move through space, when light is spread into the colors of the rainbow, or when light is focused by a lens.  Photons behave like particles when they are detected by the retinas of our eyes or are collected in a camera containing photographic film or digital detectors.  Another important property is that photons carry energy.  We know this from the common experience of feeling the warmth of sunlight when it reaches our skin.  

 

Each photon’s career as a speedster through space is stopped abruptly when it gets detected or absorbed.  This happens when photons hit the photoreceptors of our human retinas causing the visual experience.   Our ability to see depends on stopping photons.  As you read this, photons that left the page are being stopped within your eyes.  We take special pleasure in this experience when we peer into the telescopes at the New Pond Farm Observatory.  The photons coming from outer space enter the telescope, get focused through the eyepiece, and are directed into our eyes.  The images we see reveal a vast Universe with varied objects of great size and complexity existing at enormous distances away from us.  The objects we observe include planets of our solar system, comets, stars, clusters, nebula, and galaxies.  Thanks to our ability to stop photons, scientists and lay people alike can continue to learn about our amazing Universe."