Isn’t it amazing that even if we are living hundreds of thousands of kilometers away from the beautiful stars, planets, moon, and the sun, we can still know and understand a lot about them? Today, I am posting the second article the Basics of Astrophysics series. I am going to give you a brief insight into a basic scientific tool that is needed to study astrophysics. This tool is called the EM spectrum or the Electromagnetic spectrum. So, let us try to understand what is an electromagnetic spectrum and what is the importance of the EM spectrum in Astrophysics.

All the articles of Basics of Astrophysics series

The Electromagnetic (EM) Spectrum

As kids, we have been introduced to the concept of the electromagnetic spectrum. We either visualized it directly in the form of a rainbow or studied it in our elementary schools. But a rainbow just constitutes a small part called the visible region of the great electromagnetic spectrum. Let us try to understand the electromagnetic spectrum as a whole.

The EM Spectrum (Image: Byju’s)

Electromagnetic Radiation

Radiation is a form of energy that travels in the form of waves and particles, and it spreads out as it goes. Electromagnetic radiation can be defined as a stream of mass-less particles, called photons. Each photon contains a particular amount of energy and it travels in a wave-like pattern at the speed of light.

Also read: The spectral classification of stars

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The light coming from the sun, stars, even from the tube-lights at our home is an example of the visible EM radiation. The radio waves coming from a radio station help in radio transmissions and communication. The microwaves that help us heat our food in the kitchen. The ultraviolet radiation is popularized as a potential cause of skin cancer. The infra-red light, X-rays, and Gamma rays are also part of the EM spectrum that we use and harness in our daily lives.

Whenever we feel cold and try to get some warmth from the afternoon sun, we are using the infra-red part of the solar EM radiation. Whenever we have a bone injury whose exact location we need to detect, we use X-rays.

Image showing all ranges of the EM spectrum with their applications

How Do We Classify The Different Regions of An EM Spectrum?

The different types of radiation are defined by the amount of energy found in the photons. Radio waves are associated with low energy photons, microwave photons have a little more energy than radio waves, infrared photons have still more energy, then visible, ultraviolet, X-rays, and, the most energetic of all, gamma-rays. As we move along the spectrum, from radio waves to the gamma rays, the wavelength decreases while the frequency and energy increases.

Related: Decoding the universe with the gravitational waves

Importance Of The EM Spectrum In Astrophysics

Radiations in the different wavelength regions are the result of different physical processes that occur in astrophysical objects. We can learn about the distant parts of our universe by detecting and analyzing the EM radiations.

By studying the EM emissions from a distant star or galaxy that span over different regions of the EM spectrum, scientists gain crucial insights about the compositions, structure, and other properties of these objects.

The spectrum of some basic elements.

Astrophysicists use the tool of spectroscopy to determine the chemical composition of stars and planets by using their wavelength distribution. We also explained in the previous article how the dark lines in the solar spectrum by Wollaston and Fraunhofer gave birth to the subject of Astrophysics. So the roots of astrophysics lie in the EM spectrum itself.

Instruments like Hubble space telescope, Compton Gamma Ray Observatory, Chandra X-Ray Observatory, Spitzer Space Telescope, and probes like Voyager prevent the hindrance of EM radiation from remote astrophysical objects due to Earth. They help in observing the EM spectrum of the distant parts of our galaxy with high sensitivity and precision.

The spectrum is the most important tool in the hands of an astrophysicist to decode the cosmos. The study of spectra can yield enormous information. For example: By studying the stellar spectra, we can know about its chemical composition, temperature, mass, structure, distance, and density. Also, by studying it we can determine the relative motion of the star with respect to us. Radio astronomy is one of the most popular branches of this subject. Using the radio spectra, scientists explore the deepest objects in the Universe such as black holes, quasars, and galaxies.

Author’s Message

As a plasma physicist, I study different kinds of waves in space and astrophysical plasmas such as Alfven waves. Alfven waves are proposed to be responsible for the anomalous heating of the solar corona. Plasma waves are detected by satellites and spacecraft and are most amazing to explore the basic plasma phenomena in space and astrophysical objects. I hope that this article has amazed you with the simplicity of a basic but important tool that we use to study astrophysics-the EM spectrum!

Previous in series: What is Astrophysics and how is it different from Astronomy and Cosmology?

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All the articles of Basics of Astrophysics series