If we only relied on our eyes, we would be blind to most of what the universe has to offer. There would be so much that we I would completely miss, from the explosive nature of gamma-ray bursts to the dusty skeletons of galaxies and even the radiation left behind by the Big Bang. This is because the universe emits light that goes well and truly beyond what our eyes alone can see. Visible light, which is the light that we see making up our everyday surroundings, is just one small part of the electromagnetic spectrum. This runs all the way from low-energy radio waves through to astonishingly high-energy gamma rays.
Human eyes are unable to see anything that’s outside of the visible part of the spectrum, so you might be surprised to learn that we produce this hidden light on Earth, too. Think of infrared night-vision goggles, the X-rays you might get to see a broken arm, ultraviolet security tags or radio waves transmitting music and telephone calls across the planet. But in space these wavelengths of light are everywhere, coming from all kinds of cosmic objects. It’s like a hidden universe, but luckily for us, astronomers are able to tune in to these other wavelengths to make the invisible visible.
Light is a funny thing – it’s able to act like both a wave and a particle at the same time, and this is why we say that a photon of light can have a wavelength. The longest wavelengths are radio waves, which range from a millimetre in length to many kilometres. Meanwhile, the shortest wavelengths on the electromagnetic spectrum belong to gamma rays and can be as small as a trillionth
