Solar Misconceptions, Part 2: Radiation, Ray Guns, and Retinas

 

In discussing misconceptions about the sun, we need to take a step back and look at general common misconceptions about light, or what scientists more generally call electromagnetic radiation. Yes, I did say (ok, typed) the dreaded “R” word, so we’d better unpack this. Light is generated by changing electric and magnetic fields, hence the ‘electromagnetic’ part of the name. Radiation refers to any transmission of energy in the form of waves or particles. Therefore sound waves are associated with “acoustic radiation” (which does not cause cancer, despite the misconceptions concerning windmills held by certain individuals) and heat with “thermal radiation.”  The problem is that the term radiation brings to mind haunting images of Hiroshima survivors and increased cancers rates following the Chernobyl nuclear power plant accident. The colloquial use of the term radiation leads to misconceptions that all radiation is not only harmful but also human-made. From Godzilla and The Incredible Hulk to The Attack of the 50 Foot Woman and The Night of the Living Dead, the consumer of popular culture is bombarded with countless representations of the simple equality radiation = bad.

Godzilla Rock. Public domain

On the other hand, to a nonscientist, light refers to what we can see with our eyes (what physicists term “visible light”). Ultraviolet emissions pose a danger to human tissue (which is why sunscreen exists) despite being a form of light, while benign violet wavelengths of light can also be termed radiation (as can yellow, red, infrared, radio, and many other wavelengths of light). The problem is that we need to distinguish between harmful ionizing radiation (such as x-rays, gamma rays and high-energy particles) that carries sufficient energy to rip electrons off atoms and cause damage to human tissue and non–ionizing radiation such as visible light.

The Electromagnetic Spectrum. Courtesy of NASA.

We also need to separate the term ray from its science fiction usage, as a default term for either mysterious (and generally harmful) forms of energy or as a weapon (for example, in the ray guns found across science fiction media). A ray of sunlight in the visible part of the electromagnetic spectrum can be relatively benign when it falls on your skin, but can cause irrevocable damage if you stare at the sun or another bright light.

Recall that we defined radiation as the transmission of energy through waves or particles. Thanks to the wonderful, wacky world of quantum mechanics, which governs the rules of nature at subatomic scales, what we think of as a wave in common experience (such as a wave of red light) sometimes acts like a particle, while under some circumstances what we normally think of as small particles (electrons, for example) act quite wavelike. This wave-particle duality is seen in the history of nuclear physics, in the discovery of three types of radiation in the early 20^th century by physicist Ernest Rutherford. He named them alpha, beta, and gamma rays based on how easy it was for them to penetrate matter (from least to most). The alpha radiation (what we often call alpha particles) turned out to be the nuclei of helium atoms (two protons bound to two neutrons), while beta rays or beta particles are electrons or anti-electrons (also called positrons, because they have a positive electric charge). Gamma rays turned out to be very high energy waves of light. Gamma rays and positrons (beta particles) are emitted in the core of the sun, as hydrogen nuclei (individual protons) are fused to form helium nuclei (alpha particles).

Public domain

The sun also adds to another type of particle/ray activity, so-called cosmic rays. Discovered in 1912, these fast-moving particles (mainly protons and various atomic nuclei) collide with our atmosphere, the most energetic with energies up to a billion times greater than the collisions achieved in the world’s largest atom-smasher, the Large Hadron Collider. Before you reach for a hardhat or dive under a table to duck and cover to escape this ionizing radiation, realize that our planet has been bathed in these particles since its birth. Our atmosphere protects us here on the surface from the worst effects of these particles. In fact, you should only be concerned about them under two circumstances: 1) a nearby star goes supernova, and 2) you are an astronaut above the protective layer of our atmosphere. As for the first, we thankfully live in a rather boring corner of the Milky Way – any supernova we would see would merely put on a pretty light show (and set astronomers scrambling to take data). As for the second, the proper shielding of spacecraft against cosmic rays for long-term space travel (such as a mission to Mars) is an area of ongoing research. In the short term, cosmic rays impinging on the retina are the primary suspect in astronauts’ seeing bright flashes of light, even when their eyes have been closed. NASA is well aware of the potential radiation risk posed to astronauts in the ISS and is revisiting its radiation standards accordingly. Airline pilots and crew who fly frequently can also be exposed to more ionizing radiation than the general public; for this reason, the FAA monitors changes in the sun’s changing levels of emission of ionizing radiation (keyed to other changes in solar activity such as flares, coronal mass ejections, and solar energetic particle events) and can recommend that flight plans remain lower in the protective blanket of our atmosphere as needed.

The bottom line is that we should both understand and respect the role that radiation in its myriad forms plays in our lives. Don’t stare at the sun (except during a total solar eclipse) and wear your sunscreen!

Note: Some of this blog post has been adapted from my book Particle Panic!