Webb and Hubble telescopes

Source: By Aswathi Pacha: The Indian Express

The James Webb Space Telescope, NASA’s most powerful telescope, is scheduled to be rocketed into orbit no earlier than 22 December 2021. Though Webb is often called the replacement for the Hubble Space Telescope, NASA said it prefers to call it a successor.

Launched into low Earth orbit in 1990, the Hubble Space Telescope has made more than 1.4 million observations, including tracking interstellar objects, capturing a comet colliding with Jupiter, and discovering moons around Pluto. Hubble has captured galaxies merging, probed supermassive black holes and has helped us understand the history of our universe.

Here we explore some of the major differences between Webb and the Hubble Telescope.


The James Webb Space Telescope, carrying four scientific instruments, will observe primarily in the infrared range and provide coverage from 0.6 to 28 microns. The instruments on Hubble see mainly in the ultraviolet and visible part of the spectrum. It could observe only a small range in the infrared from 0.8 to 2.5 microns.

The infrared region of the electromagnetic spectrum covers the wavelength range from approximately 0.7 to a few 100 microns.

Size comparisons

Webb’s primary mirror has a diameter of 6.5 metres. Hubble’s mirror was much smaller – 2.4 metres in diameter. So, Webb will have a larger field of view compared to the camera on Hubble. Webb also carries a large sun shield measuring about 22 metres by 12 metres – about the size of a tennis court.


Hubble orbits around the Earth at an altitude of ~570 km. Webb will not orbit the Earth. It will orbit the sun at about 1.5 million kilometres away from Earth. As the Earth orbits the Sun, Webb will orbit with it – but it will stay fixed in the same spot with relation to the Earth and the Sun.

How far will Webb see?

NASA says, “Hubble can see the equivalent of “toddler galaxies” and Webb Telescope will be able to see “baby galaxies”.” Webb’s near- and mid-infrared instruments will help study the first formed galaxies, exoplanets and birth of stars.

Webb vs Herschel Space Observatory

In 2009, the European Space Agency launched an infrared telescope named the Herschel Space Observatory.

It also orbits the Sun similar to how Webb would. The primary difference between Webb and Herschel is the wavelength range: Webb goes from 0.6 to 28 microns, while Herschel covers 60 to 500 microns.

Also, Herschel’s mirror is smaller than Webb’s. It is 3.5 metres in diameter, while Webb’s primary mirror has a diameter of 6.5 metres.