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As a cosmic photographer, NASA's Hubble 
Space Telescope has taken over a million  

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snapshots documenting the universe. 
These images illustrate, explain,  

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and inspire us with their grandeur, but may 
not match what we'd see with our own eyes.  

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That's because Hubble sees 
light beyond our sensitivity.

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Our eyes only sense a small 
fraction of the universe's light.

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This tiny band of wavelengths, called the 
visible spectrum, holds every color in the rainbow.

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Light outside that span, with longer or 
shorter wavelengths, is invisible to our eyes.

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But those invisible wavelengths can 
tell us so much more about the universe.

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Hubble houses six scientific instruments that 
observe at different wavelengths. Together,  

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they expand our vision into 
infrared and ultraviolet light.

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That doesn't mean Hubble can show us 
never-before-seen colors. In fact,  

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the telescope can only see the 
universe in shades of gray.

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Seeing in black and white allows Hubble to detect  

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subtle differences in the light’s intensity. 
If one wavelength is brighter than another,  

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that tells us something about 
the science of that object.  

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But, because color helps humans interpret what 
we see, NASA specialists work to process and  

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colorize publicly available Hubble 
data into more accessible images. 

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When Hubble snaps a photo, it puts 
a filter in front of its detector,  

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allowing specific wavelengths to pass through.

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Broadband filters let in a wide range of light.

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Narrowband filters are more selective,  

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isolating light from individual elements 
like hydrogen, oxygen, and sulfur.

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Hubble observes the same object multiple times 
using different filters. Image processors then  

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assign those images a color based 
on their filtered wavelength. The  

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longest wavelength becomes red, medium 
becomes green, and the shortest blue,  

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corresponding to the light sensors in our 
eyes. Combining them gives us a color image,  

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showcasing characteristics we 
can't make out in black and white.

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Adding color reveals the underlying science 
in every image. It’s like translating words  

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into another language, making sure no 
information is lost. Some words have an  

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exact counterpart—the meaning remains the same 
when you swap them. Hubble's true-color photos  

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are like that. They are a direct translation, 
using broad filters in wavelengths we can see.

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Other words can't be translated directly. When we  

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use narrowband filters or peer 
outside the visible spectrum,  

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it's like translating words with no one-word 
replacement. Easily done, but requires more work.

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Narrowband images highlight the concentration of 
important elements. Infrared images are like heat  

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maps, helping us spot newborn stars in dark, dusty 
clouds and peer further back in time and space.  

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In ultraviolet, we uncover active aurorae on Jupiter 
and learn how young, massive stars develop.

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Image processors also clean up 
artifacts—signatures in an image  

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that aren't produced by the observed target.  
As sensors age, some pixels become imperfect,  

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returning too much electrical charge, or 
not enough. Artifacts can leave behind odd  

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shapes or return images without any true black. 
These effects can be calibrated and removed. 

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Other artifacts come from the dynamic environment 
of space. Even the best photographers get  

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photobombed; in Hubble's case, the culprits 
are asteroids, spacecraft or debris trails,  

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and high-energy particles called cosmic rays. 
By combining and aligning multiple observations,  

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image processors can identify them and 
piece together an artifact-free image.

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Without processing, many Hubble images 
would be divided down the middle.  

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This line, called a chip gap, is the tiny space 
between some camera sensors. Hubble moves slightly  

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with each observation, allowing image processors 
to fill the gap and replace faulty pixels.

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And because there's no 
natural up or down in space,  

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processors decide how to 
rotate and frame the image.

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It's a time consuming procedure. 
Simple images take about a week,  

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while large mosaics, stitched together from 
many observations, can take a month to process.

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Hubble images may not be what we'd see 
firsthand. Instead, they are tools for  

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understanding science at a glance, shedding light 
on otherwise invisible views of our universe.

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Follow us on social media @NASAHubble