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In a Different Light: The Night Sky

The extremely faint, low-energy light, known as the cosmic microwave background radiation; it is the afterglow of the big bang that formed the universe some 13.8 billion years ago.


Produced by the Space Telescope Science Institute’s Office of Public Outreach in collaboration with NASA’s Universe of Learning partners: Caltech/IPAC, Center for Astrophysics | Harvard & Smithsonian, NASA Jet Propulsion Laboratory, and Sonoma State University

  •  Image of Milky Way from Earth (infrared): NASA’s Wide-Field Survey Explorer (WISE)

  • Image of Milky Way from Earth (gamma ray): NASA’s Fermi Gamma-ray Space Telescope

  • Image of mottled sky (microwave): Planck Space Telescope 


Text, In A Different Light, The Night Sky, Electromagnetic Spectrum.
A photo of a starry sky. A bar across the bottom of the screen reads, Radio, Microwave, Infrared, Visible, Ultraviolet, X-ray, Gamma Ray.
Text, On a clear night, far from the glare of artificial lights, thousands of stars light up the sky. Some form familiar patterns.
Text, Many stars are concentrated in a broad band, the disk of our Milky Way galaxy, which we see from within. Human eyes can detect the visible light of more than 6,000 stars in the Milky Way that surrounds us. But there is more to the night sky than meets the eye.
The word Visible is highlighted.
Text, The sky glows with colors of light that are absorbed by Earth's atmosphere and colors that human eyes cannot detect. What might the night sky look like if we could see through the atmosphere and detect invisible colors, like infrared light, gamma rays, and microwaves?
A blue glowing version of the photo. Infrared is highlighted.
Text, NASA's Wide-Field Infrared Survey Explorer, WISE, provides an infrared view of the sky.
The disk of the Milky Way glows brightly in the infrared light emitted predominately by stars.
Dust that is too cold to give off visible light is warm enough, heated by nearby stars, to glow infrared. A colorful cluster is labeled, Dusty Nebula.
A bright yellow red and blue version of the photo. Gamma Ray is highlighted.
Text, NASA's Fermi Gamma-ray Space Telescope allows us to see the highest-energy light in the universe.
With Fermi, we can detect energy from stars that have exploded and stars in the process of merging.
Supermassive black holes at the centers of distant galaxies.
And sudden gamma-ray bursts, the most powerful explosions occurring in the universe.
Many of the gamma-ray sources lie far outside the Milky Way, within distant galaxies billions of light-years away.
While Fermi reveals the most energetic energy traveling through the universe, the Planck Observatory gives us a view near the other end of the spectrum.
A red and blue splotchy version of the photo. Microwave is highlighted.
Text, When the energy from the Milky Way is removed, Planck's keen microwave vision reveals a mottled sky.
The slight variations in microwave radiation correspond to minute differences in temperature. The red splotches are labeled warmer, and the blue splotches are labeled cooler.
Text, This extremely faint, low-energy light, known as the cosmic microwave background radiation, does not come from particular stars, galaxies, or clouds of gas and dust.
It is the afterglow of the big bang.
A relic of the event that formed the universe some 13.8 billion years ago.
A normal version of the photo. The word visible is highlighted.
Text, Human eyes are sensitive to only a small fraction of the light that fills the universe.
Space telescopes give us the ability to detect invisible colors.
Like infrared light.
Gamma rays.
And microwaves.
Studying the broad spectrum of light helps us better understand what our universe is made of and how it changes over time.