The Electromagnetic Spectrum

Like expanding ripples in a pond after a pebble has been tossed in, electromagnetic radiation crisscrosses the universe, in the form of waves. And those waves are traveling at the speed of light, which is 186,000 miles per second. 

Electromagnetic waves are produced when charged particles are accelerated. They are a combination of electric and magnetic fields that create self-propagating and oscillating waves that move perpendicular to each other. 

Unlike water and sound waves, which need a medium, electromagnetic waves use no energy.

The Electromagnetic Spectrum covers a wide range of frequencies. From radio waves, which has a wavelength of meters, to gamma rays, which have wavelengths on the order of picometers. 

Radio waves have the longest wavelengths in the electromagnetic spectrum. They range from the length of a football to larger than Earth. Radio waves are a form of light, as proved by Heinrich Hertz, a German physicist in the 1880s.

German physicist Heinrich Hertz proved the existence of radio waves in the late 1880s. In his experiments, he showed that radio signals possessed all of the properties of electromagnetic waves and their velocity was equal to the velocity of light.

To listen to your favorite music, you tune a radio to a specific frequency. It then “receives” electromagnetic radio waves and converts them to mechanical vibrations in a speaker or headphones to create sound waves.

Radio telescopes are designed to receive radio waves from outer space. By studying this data, radio astronomers can learn about a celestial composition, structure, and motion. Radio astronomy also has the advantage that sunlight, clouds, and rain don’t affect observations.

Microwaves are a portion of the electromagnetic spectrum, and are basically extremely high frequency radio waves. They have frequencies ranging from about 3 billion cycles per second, or 3 gigahertz (GHz), up to about 30 terahertz (THz).

They are distinguished from radio waves by the technology used to detect them.

The entire sky, a source of microwaves in every direction, is most often referred to as the cosmic microwave background (CMB). These microwaves are remnants of the Big Bang. 

They tell us about galaxy formation, stellar and planetary system birth, and the solar system’s composition.

Humans, at normal body temperature, radiate most strongly in the infrared at a wavelength of about 10 microns (one millionth of a meter). Cold-blooded animals, such as lizards will take on the temperature of their environment and are more difficult to detect in infrared.

Electromagnetic radiation, which sounds like something you should avoid, actually supports our senses by providing the light emissions through which your eyes perceive the world. 

All electromagnetic radiation is called light, but this light should not be confused with optical light that we detect with our eyes.

Chlorophyll, found in almost all types of plants, absorbs all of the colors of the light spectrum. Since it cannot absorb the color green, this is what we see reflected on leaves, stems, etc.

Because Earth's atmosphere absorbs much of the high-energy ultraviolet radiation, scientists use high-altitude balloons and satellites with specialized imaging sensors to detect UV radiation. 

At these wavelengths, scientists can study the formation of stars since young stars shine most of their light in ultraviolet.

Machines that deal with currency often use UV light to detect counterfeit money. Governments have added UV ink into their bills, in order to make it harder to copy them and easier to identify fakes.

German scientist Wilhelm Conrad Roentgen first observed X-rays in 1895. His experiments showed that this unknown radiation could penetrate soft tissue, but not bone. One of the most common and beneficial uses of X-rays is for medical and dental imaging.

Since the Earth's atmosphere blocks X-ray radiation, satellites with X-ray detectors must be positioned high above Earth's atmosphere. Such X-ray astronomy measurements provide clues as to the composition, temperature, and density of these distant celestial environments. 

Gamma rays can be produced by fusion and fission reactions. Nuclear fusion is the reaction that powers the sun and stars. This high-energy form of radiation can damage human tissue and cause mutations, but it can also be used to treat cancerous tumors. 

Fusion, fission, alpha decay, and gamma decay are all nuclear reactions that produce gamma rays. In space, gamma rays come from nuclear reactions produced by stars, supernova explosions, and regions around black holes.