How is the Webb telescope different from the Hubble? The images tell the story

The James Webb Space Telescope is not a replacement for the Hubble Space Telescope. It's a successor inspired by Hubble’s previous results.

It's the next step in answering the question: “What’s up there?”

And it's not just “better” the way a 2022 digital camera is better than one from 2005.

Hubble produces images primarily by looking at light in the visible and ultraviolet spectrums of light — that is to say light that humans can see and light with shorter wavelengths. Webb creates images in the infrared and near-infrared spectrum — light with wavelengths longer than light visible to humans.

Hubble (left) Webb (right): The Southern Ring Nebula as captured by Hubble in 2005 (left) and Webb in 2022 (right). This nebula is formed from layers of gas and dust cast off by a collapsing star over thousands of years. Webb’s image throws these rings into sharp relief.

This is an important difference due to the way light changes as it travels across the universe.

Without getting too deep into the weeds of general relativity, the light is stretched as it travels. This stretching increases the wavelength of the light, moving it from the visible spectrum toward infrared. By being able to see more of the infrared spectrum, Webb can see objects that are more distant than Hubble can.

Hubble (top) Webb (bottom) — A portion of the “Cosmic Cliffs” of the Carina Nebula as captured by Hubble (top) and Webb (bottom). The infrared image from Webb allows us not only to see far greater detail, but to pierce through the nebula’s clouds and see numerous objects beyond.

To complicate things just a bit more, when we see objects farther away, we are actually seeing older objects. This is because light takes time to travel, so by the time it reaches us here on Earth we are not seeing a distant star as it is today, but as it was thousands or millions of years ago. For example, the Cosmic Cliffs region of the Carina Nebula (top of the page) is roughly 7,600 light years away from us. So that image isn’t what the cliffs look like today, but what they looked like 7,600 years ago when that light left the nebula.

This means Webb is essentially letting us see further back in time. As one NASA article put it: “Essentially, Hubble can see the equivalent of 'toddler galaxies' and Webb Telescope will be able to see 'baby galaxies.'"

The Universe contains some truly massive objects. Although we are still unsure how such gigantic things come to be, the current leading theory is known as hierarchical clustering, whereby small clumps of matter collide and merge to grow ever larger. The 14-billion-year history of the Universe has seen the formation of some enormous cosmic structures, including galaxy groups, clusters, and superclusters — the largest known structures in the cosmos! This particular cluster is called Abell 665. It was named after its discoverer, George O. Abell, who included it in his seminal 1958 cluster catalogue. Abell 665 is located in the well-known northern constellation of Ursa Major (The Great Bear). This incredible image combines visible and infrared light gathered by the NASA/ESA Hubble Space Telescope using two of its cameras: the Advanced Camera for Surveys and the Wide Field Camera 3. Abell 665 is the only galaxy cluster in Abell’s entire catalogue to be given a richness class of 5, indicating that the cluster contains at least 300 individual galaxies. Because of this richness, the cluster has been studied extensively at all wavelengths, resulting in a number of fascinating discoveries — among other research, Abell 665 has been found to host a giant radio halo, powerful shockwaves, and has been used to calculate an updated value for the Hubble constant (a measure of how fast the Universe is expanding). — A deep field image captured by Hubble (left) and by Webb (right). This is the same region of space, but Webb’s infrared imaging shows many more objects. The redder the object in the image, the further away it is, and the further back in time we are looking when we view it.