Measuring the Color of Stars

In astronomy, a star’s color tells its story. Measuring the color of a star gives astronomers immense insights into its temperature, age and composition even from hundreds of thousands of miles away. By measuring stars’ wavelengths, you can determine their elemental makeup and main components.

What Is Astronomical Spectrophotometry?

Spectrophotometry refers to the process of measuring a sample’s electromagnetic wavelengths to determine information such as color, chemical composition and age. Every element in a star emits a unique wavelength of electromagnetic radiation, which allows spectrophotometry to examine the percentage of hydrogen, helium and trace elements in a star. Astronomical spectrophotometry uses Planck’s curve to examine a star’s peak wavelength and understand components of its makeup, which are impossible to judge from Earth.

Since stars are powered by nuclear fusion at their core, they maintain a steady dynamic equilibrium throughout their life and display their life cycle position using color. Due to this uniform time and color cycle, you can determine a star’s age by its hue. Though all stars appear white due to their peak wavelength on the color spectrum, many are blue, yellow, red and green. The following star colors correspond with the listed heat levels in Kelvins: 

  • Blue stars: 10,000-50,000 K
  • Yellow stars: 5,500 K
  • Bright red stars: 3,500 K
  • Dark red stars: 2,500 K

What Can a Star’s Color Tell Me About Stellar Evolution?

Each star goes through a stellar evolution in its lifetime, meaning its temperature, size and color will change as it grows older. After a nebula becomes a star, it goes through a sequence where it turns into either a yellow low- or medium-mass star or a white high-mass star. Yellow low- and medium-mass stars then become red giants before transforming into planetary nebulas and phasing into white dwarfs.

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During the planetary nebula stage, many stars become bluish-green in color. High-mass stars grow from their white main sequence into a red supergiant before becoming a supernova and then a black hole. 

Many stars remain in their main sequence for six to 12 trillion years before experiencing a red giant or supergiant phase. However, other supergiant stars may burn faster due to their exhaustive supply of hydrogen and will become massive supernovas and nebulas instead of red supergiants. While stellar evolution may not always progress on the same path, a star’s color can still tell us its heat level and stage in stellar evolution.

Learn More About the Color of Stars With HunterLab Products

HunterLab has had a passion for truth and innovation for over six decades. We’ve spent our careers pioneering advances that took science to a whole new level and created tools that spectrophotometry has come to rely on. We’re committed to quantifying what was previously thought unquantifiable and creating spectrophotometry instruments that bring you closer to understanding the truths of the universe. 

To learn more about our astronomical spectrophotometers and how our equipment can assist you, contact us online today