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Astronomical Spectroscopy

Author: Emily Jiang

Editors: Misha Wichita and Chiara Chen

Artist: Acey Li

Have you ever wondered how scientists figured out the compositions of far away planets or even objects’ speeds in space? These values can be found by using spectroscopy, a method used to study objects based on the patterns of colors and their corresponding wavelengths. Spectroscopy consists of studying the spectra, or patterns of colors, that objects reflect, absorb, release, or transfer, and it can be used to find the temperatures, speeds, compositions, and density of objects in space. 

X-rays, ultraviolet light, visible light, infrared light, gamma rays, microwaves, and radio waves are forms of light called electromagnetic radiation. These forms of light collectively make up the electromagnetic spectrum. The electromagnetic spectrum shows how light is spread out into different colors ranging from warm to cool colors. Different objects produce light, and due to their varying temperatures and compositions, they exhibit distinct spectra. There are multiple types of spectra: continuous, reflectance, emission line, and absorption. Spectra shows how the brightness of light changes with the wavelength. 

Continuous spectra are regions where brightness changes from one color to another color. The blackbody curve is one type of this spectrum, where an object releases a band of colors based on its surface temperature. Hotter stars release more blue light than red light and appear more blue at night, while cooler stars emit more red light and appear more red at night. 

Absorption spectra are where certain colors are much dimmer than other colors and, at times, these colors appear not to be there at all. These nearly invisible colors appear as black lines, known as absorption lines, and the intensity of these lines displays the composition and temperature of the object, along with the density of the gas. Furthermore, the transmission spectra is a type of absorption spectrum in which starlight passes the atmosphere of a planet and some of the light is transmitted through the atmosphere. The amount of light transferred shows how warm and dense the atmosphere may be. 

Emission spectra are mainly black with brightly-colored lines, otherwise known as emission lines. These lines correlate with specific atoms, and each atom releases a specific pattern of color or spectra. Emission spectra allow scientists to study clouds of hot gas and observe the brightness of different emission lines that show the temperature, density, and elements in a gas. 

Reflectance spectra display the colors that reflect off the surface of objects, allowing planetary scientists to determine the compositions of objects such as planets, moons, asteroids, and comets. The material reflects a pattern of colors depending on the roughness, shape, orientation, and type of color the material is absorbing and transferring. 

Through the predicted and particular ways light and matter interact, spectroscopy can help us understand the universe around us. Matter emits light and the different wavelengths of light that matter interacts with is what makes each material look different from one another. Astronomical spectroscopy helps scientists comprehend how neutron stars, black holes, and active galaxies produce light, specific speeds, and the compositions of these objects in space. 



Spectroscopy intro. “Spectroscopy 101 – Introduction | Webb.” Webbtelescope, NASA and

Spectroscopy Light and Matter. “Spectroscopy 101 – Light and Matter | Webb.”

Webbtelescope, NASA and STScI, 7AD,

Spectroscopy Types. “Spectroscopy 101 – Types of Spectra and Spectroscopy | Webb.”

Webbtelescope, NASA and STScI, 7 July 2022,

What can they Tell us. “Spectra and What They Can Tell Us.” NASA, NASA, Aug. 2013,

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