Are astronomers ignoring some of the cosmos?
The UniverseFridays
May 15, 2026
6 min read
Add Us On GoogleAdd SciAm
Are astronomers ignoring some of the cosmos?
There are parts of the universe, and of the electromagnetic spectrum, that we’re not covering with our telescopes—but not as many as you might think!
By Phil Plait edited by Lee Billings
DNY59/Getty Images
Stay connected to The Universe: Get email alerts for this weekly column by Phil Plait
Enter your email
I agree my information will be processed in accordance with the Scientific American and Springer Nature Limited Privacy Policy. We leverage third party services to both verify and deliver email. By providing your email address, you also consent to having the email address shared with third parties for those purposes.
Sign Up
It’s a big universe out there. But with astronomers churning out noteworthy cosmic discoveries and insights each and every day, you might think we’ve somehow got it all covered, with the collective might of Earth’s telescopes giving us full situational awareness of the sky.
Nothing could be further from the truth. Despite the existence of all our advanced observatories, there are still parts of the electromagnetic spectrum (and beyond) that we’re not seeing and places where we need more (or any) telescopes.
By definition, the spectrum—that is, different kinds of light—is essentially infinite in range. But even so, the visible span of the spectrum from violet to red is only about a factor of two in wavelength, while the huge range from long-wave radio to gamma rays covers more than 20 orders of magnitude. So it shouldn’t be surprising that we don’t have it all covered.
On supporting science journalism
If you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.
What’s more surprising, in fact, is just how much we have managed to cover! There are thousands of visible light telescopes in operation at any given time; I have a personal one I use myself when the bugs outside aren’t too bad. Professionally speaking, there are dozens of large observatories on the ground and orbiting above it, and quite a few next-generation facilities in the pipeline—including the soon-to-be launched Nancy Grace Roman Space Telescope, which will have the Hubble Space Telescope’s sharp vision coupled with a vastly larger field of view. And archival data are important to note, too, because most things in the sky don’t meaningfully change on human timescales, making thorough surveys still relevant even if they’re years or decades in the rearview.
For example, in infrared we had the Wide-Field Infrared Survey Explorer, which scanned the whole sky to give an overview, and, of course, we still have the James Webb Space Telescope giving us the sharpest, deepest views yet in that spectral range. The Wilkinson Microwave Anisotropy Probe (WMAP) and the Planck observatory mapped the sky in microwaves; today the Atacama Large Millimeter/Submillimeter Array (ALMA) covers smaller wavelengths. And overall there are almost as many operational radio telescopes as there are visible-light ones.
At the other end of the spectrum, the Galaxy Evolution Explorer (GALEX) surveyed the sky in ultraviolet, and Hubble has two UV cameras still in operation. Several orbiting telescopes detect x-rays, including the venerable Chandra X-ray Observatory, XMM-Newton, Neil Gehrels Swift Observatory, and more. Even gamma rays get their day in the sun (so to speak), with the Fermi Gamma-Ray Space Telescope and Swift still operating and producing amazing data.
There are some holes in our coverage, but even those have proposals to fill them. One of the most glaring gaps lies between the infrared and millimeter-wavelength radio observations, but the Probe Far-Infrared Mission for Astrophysics (PRIMA) would fill much of it. Another gap exists for radio waves with wavelengths of 10 meters or more, which are reflected by Earth’s ionosphere; to observe these, astronomers have proposed building radio telescopes on the moon’s far side. One, called the Lunar Crater Radio Telescope, would be a staggering kilometer across. Such telescopes would be sensitive to radio waves emitted by gas from the cosmic “Dark Ages,” the period a few hundred million years long after the big bang but before the first stars were born, an era we know very little about.
And even for the parts of the spectrum already thoroughly covered, it’s not necessarily greedy to still want more! Different telescopes have different functions. Some look at wide areas of the sky to do surveys, while others pinpoint specific targets; some take images, while others take spectra, dividing the incoming light into different energies (or colors, wavelengths or fr