Today’s column is an introduction to the electromagnetic spectrum (EM), an understanding of which can be very illuminating (pun intended).
The National Aeronautics and Space Administration at nasa.gov/science defines electromagnetic radiation as a stream of massless particles called photons, traveling in a wavelike pattern at the speed of light. Each type of radiation is described by its signature wavelength.
At the short wavelength end of the spectrum are gamma rays, with wavelengths shorter than an atom’s nucleus. Gamma rays travel only a few tens of yards but can penetrate and damage living tissue. Next in length to gamma rays are x-rays, which are produced by radioactive substances. X-rays, PET scans, MRIs, and CT scans are all medical imaging techniques that use short wavelength radiation to examine tissues and metabolic processes inside the body.
Next on the spectrum, visible to some living things but not humans, is ultraviolet radiation. Ultraviolet light can cause skin cancer and cataracts, but some insects and some mammals, including dogs and cats, see this portion of the spectrum. The melanin in our skin helps to shield us from UV damage. Darker skin tones, sunblock, hats and sunglasses provide even more protection from UV radiation.
Between the ultraviolet and the infrared portion of the spectrum is visible light. Science students often learn the “ROY G. BIV” acronym to remember the rainbow of visible light from the longest to the shortest wavelengths (red, orange, yellow, green, blue, indigo and violet). Space heaters, television remotes and clothes dryers use the infrared portion of the spectrum, and night vision goggles work by sensing infrared rays given off by body heat.
Beyond visible light are microwaves and radio waves, used for cooking our food, communicating with cell phones, and exploring the galaxy.
At the long wavelength end of the spectrum are the radio waves, which are produced by any object in the universe that has a changing magnetic field. Radio waves travel indefinitely through space and do not damage living tissue. Radar uses radio waves to locate objects and determine their speed and direction.
Our nearest star, the sun, is the major source of most of the electromagnetic energy on Earth. The nuclear fusion process occurs when hydrogen fuses into helium in the sun’s core, releasing vast amounts of radiation — mostly in the ultraviolet, visible light, and infrared range.
A young star emits a brilliant bluish-white light; a middle-aged star (like our sun) emits a yellowish light, and a dying star turns from orange to red as it exhausts its fuel source.
Over the next five billion years, our sun will convert all its hydrogen to helium, becoming a “red giant,” and life on planet Earth will have ceased. Proof that life once existed here, however, will dance through space in the form of radio waves that may be detected by a more intelligent life form.
