Fourth anniversaries aren’t often causes for celebration. But in the case of the James Webb Space Telescope (JWST), which launched on Dec. 25, 2021, this anniversary marks an important transition.

Until now, JWST has been in discovery mode. A generation in the making at a cost of $9.7 billion, it is the most powerful telescope in history, capable of observing at distances and levels of detail without precedent. 

But as with any major new scientific instrument, astronomers needed to see JWST in action before they could answer the fundamental question that will drive research for decades to come: How much of our universe can we see?

The JWST builds on the progress the Hubble Space Telescope has made since its own launch, in 1990. The Hubble primarily observes space through the visible region of the light spectrum—the part that our eyes have evolved to see. JWST, however, sees primarily in the infrared, allowing it to penetrate cosmic dust, observe cooler objects, and peer into the early universe.

Because the speed of light is finite, observing objects at greater and greater distances means seeing farther and farther into the past. And because the expansion of the universe—the expansion of space itself—has stretched the visible light from the most distant objects into the infrared, JWST can search for the first sources of........

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