Along with a hundred scientists from the Harvard-Smithsonian Center for Astrophysics, I watched the live broadcast from the center’s Phillips Auditorium. We already had the Hubble telescope in space. Now we also have James Webb. When you spend $9 billion on a new telescope, you don’t want it to be a little better than the old one. So why is Webb so much better than Hubble? This was the first question that came to me. My neighbors in the audience responded very nicely.

Webb is older. Hubble’s light collector is 4 m2. Webb’s is 25 m2. So Webb collects 6.2 times more light. Webb is better placed. Hubble orbits the Earth, 550 km above our heads. Thus the Earth itself hides part of the sky from it [1]. As shown in the figure below (not to scale), Webb is at the L2 “Lagrange point”, about 1.5 million kilometers from Earth. The result is that no part of the sky is hidden by Webb. Hubble is sensitive to visible light. Webb is sensitive to infrared light. Here is a very clear comparison of the 2 sensitivity ranges. Infrared light penetrates best through the gas and dust found in the universe. Furthermore, the redshift of very distant objects means that their light reaches us in the infrared. Finally, “cool” objects, such as exoplanets, tend to emit infrared light. Infrared detectors require a low and stable temperature. The L2 point provides this of course. An earth orbit does not.

These strengths should allow progress in the study of the aforementioned objectives:

Distant universe: first stars and galaxies formed after the Big Bang, galaxy formation and evolution. “Cold” target: star and planet formation, extrasolar planetary systems.

Meanwhile, the first images are impressive. My neighbors, who would have every reason to be bored as they spend their lives studying these pictures, couldn’t help but ooh and aah when they saw Webb’s pictures.

The loudest exclamations were for the image below. For comparison, I put the same, taken by Hubble. I don’t need to add anything else. Photo of the Carina Nebula taken by the James Webb Space Telescope. / NASA.
Photo of the Carina Nebula taken by the Hubble Space Telescope. / NASA.
Antoine Bret, Professor of Physics at the University of Castilla-La Mancha (Spain).

  1. If the Earth were a basketball, Hubble would be 2 cm from its surface. This means that almost half the sky is permanently hidden by it.