Astronomers can't see everything. But not for lack of trying

"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."

"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,"

Astronomical observations do not provide complete situational awareness of the sky because many parts of the electromagnetic spectrum and some regions of space remain unseen. The spectrum extends infinitely in principle, and even practical ranges span enormous wavelength differences. Visible light covers only a small factor in wavelength, while radio through gamma rays spans more than 20 orders of magnitude. Despite advanced observatories, more telescopes are needed in certain wavelengths and places. Thousands of visible-light telescopes operate, and dozens of large ground and space observatories exist, with additional facilities planned. Archival data remain valuable because many celestial targets change slowly on human timescales, making past surveys still useful for current research.

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