A horizontal, two-panel image of pixelated, black-and-white star fields. The left image label is: “Webb Near-IR.” It holds a few dozen points of light of varying brightness. At the center of the image, a circle marks one bright point. The right image label is: “Hubble Near-IR.” It holds more indistinct, blurry patches whose overall brightness is similar to the more defined regions in the left image. At center, a circle marks a light gray pixel.

Cepheid Variable Star P42 in NGC 5468

At the center of these side-by-side images is a special class of star used as a milepost marker for measuring the universe’s rate of expansion – a Cepheid variable star. The two images are very pixelated because they are a very zoomed-in view of a distant galaxy. Each of the pixels represents one or more stars. The image from the James Webb Space Telescope is significantly sharper at near-infrared wavelengths than Hubble (which is primarily a visible-ultraviolet light telescope). By reducing the clutter with Webb’s crisper vision, the Cepheid stands out more clearly, eliminating any potential confusion. Webb was used to look at a sample of Cepheids and confirmed the accuracy of the previous Hubble observations that are fundamental to precisely measuring the universe’s expansion rate and age.

Credits: NASA, ESA, CSA, STScI, Adam G. Riess (JHU, STScI)