Astronomy Jargon 101: Electromagnetism

In this series we are exploring the weird and wonderful world of astronomy jargon! There’s a lot to see with today’s topic: electromagnetism!

We’ve known about features of the electromagnetic force for a long time. We knew that the Sun generated light (and we debated if the Moon did too). We knew that we felt warm by the fire. We had discovered “lodestones”, which were seemingly magical rocks that would always point North. We witnessed lightning and were wary of electric eels.

Over time, we came to understand even more, especially through scientific investigation. We found that light could be described as a wave, and that white light could be split into the colors of the rainbow. We discovered infrared radiation, which was invisible to us but acted exactly like any other light. We realized that the electricity in lightning was exactly the same as the electricity flowing through our nerves. We deduced that strong magnets could create weaker ones in special types of materials.

Beginning in the 1800’s, we slowly started to realize that all of these were connected. Running electricity through a loop of wire generated a magnetic field. A magnet passed through the center of the same hoop could generate an electric current. Two electric wires would attract or repel, exactly as two magnets could.

It was Scottish physicist James Clerk Maxwell who figured it all out in the 1860’s. He developed a theory of electromagnetism that united all these disparate phenomena under a single theory. It was the greatest act of physical insight since Isaac Newton’s discovery that gravity was universal.

Maxwell’s work gave us the electromagnetic force. The force that keeps the magnet on your fridge is the exact same force that powers your cell phone. It’s also the exact same force responsible for light; Maxwell realized that what we call light is just a bunch of electric and magnetic waves traveling together.

The electromagnetic force is, along with gravity, the most familiar of the four forces of nature. Today we know that the force is carried by photons, which are massless particles that have infinite range and travel at the speed of light. Complex interactions of photons are responsible for the entire rich variety of electromagnetism.