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What Is The Difference Between Emission Spectra and Absorption Spectra?

Leonard Kelley holds a bachelor's in physics with a minor in mathematics. He loves the academic world and strives to constantly explore it.

Light and the Rainbow

Everything that you see around you is a result of light.

No, let me be clear about that.

It is not that light created all that you see but that without light you wouldn't be able to see anything at all. By having the light bounce off objects and into your eyes, you gain information about what you are seeing. Similarly, scientists use the light from objects to learn more about them. By using a spectrometer, or a wavelength diffuser, scientists can take a beam of light and break it down to the wavelengths that are present. This spread of wavelengths is called a spectrum. Depending on the type of object though they will be looking at a different type of spectrum.

These spectrum are best represented with the colors of the rainbow. Depending on the wavelength of the light, the color will vary with it. The red portions of light are low-wavelength and have less energy than the blue portion, which has short wavelengths. But unlike a rainbow, most spectrums will not contain the entire color range but may have little gaps in certain wavelengths. Other times, we may only see little portions of the spectrum and have the rest of it black. These are the two main types of spectrums known as absorption and emission, and both have equally important roles as tools in astronomy.


Emission Spectrums

These spectra appear as thin bars in the spectrum, very spread out and sparse. The source of an emission spectrum is the result of excited electrons in a gas. These electrons in the elements orbit protons and neutrons (collectively forming the nucleus of the atom) almost like planets around a star. Depending on the state of the electron, it will move closer or further to the nucleus depending on the energy present. Electrons like to be in a low-energy state and typically will do anything to get there, including giving up energy. They release that energy in the form of light and then fall to the lower orbit. Depending on how much energy they give up, the type of light they give off will also be different. So sometimes a specific element can have multiple possible spectrums. Many people may wonder how long an element can generate such light for the electrons can only fall so far in their orbitals. Because of random collisions between each other and random particles, plenty of energy gets restored to the system and the process continues.

Absorption Spectrums

These spectra appear as a nearly complete spectrum with a few lines missing from place to place. The source of an absorption spectrum also lies in the state of the electrons but in this case it is them receiving energy. When photons hit objects it transfers energy to the particles present. Depending on the element present it will absorb a specific amount of energy. This absorption takes place with the electrons which upon receiving the energy will be able to achieve a higher-energy orbital. Those photons are no longer present and when we see the spectrum the gaps present are those wavelengths of light that have been absorbed by the element. These spectra typically occur in a high-light environment.

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Uses of the Spectrum

Frequently, the study of these spectra is used in astronomy. When we look at the stars we frequently see absorption spectra. In fact, it was through the spectra of the sun that we noticed that wavelengths were missing. These lines in the spectra did not correspond to any known element at the time. Later on, it was determined that a new element had been discovered and it was named in honor of Helios (the sun god), hence why it is called helium.

Also, nebula have spectra profiles. Depending on the composition of the nebula (whether it is mostly gas or dust) and how many stars are present, we will get different types of spectra. We also use them on our studies of the planets. We can learn much about their chemical makeup and their history through spectra. Light truly reveals hidden wonders all around us.

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

© 2014 Leonard Kelley

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