Thursday, June 30

How are the two space telescopes different?




After more than three decades in space, the Hubble has provided us with incredible snapshots, such as the mythical nebula of the pillars of creation, detailed images of the rings of Saturn or the first photographs of the heart of the Milky Way. And not only that: thanks to him we have been able to verify that supermassive black holes are everywhere, in the center of galaxies; that there are clusters that, like nurseries, are generating new stars and that have all kinds of shapes and sizes; and that the universe is expanding and accelerating more and more, rewriting everything we thought we knew about space.

For all this, the bar is very high for the James Webb.

The new space telescope, which will be launched next Saturday, December 25 from the French Guiana, promises new images and science much more spectacular and complex than its predecessor. But, what differences exist between one and the other?


One of the vital components of any telescope is its mirror: Hubble features an imposing 2.4-meter panel. However, the James Webb has a 6.5 meter ‘super mirror’ made up of 18 gold-coated beryllium pieces each 132 centimeters in diameter. “This means that Webb will be able to study the Universe in much more detail,” he explains to ABC. Macarena Garcia Marin, ESA scientist for the development and scientific support and calibration of MIRI / JWST, one of the key instruments of the new space telescope.

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In addition, in total the Webb (which measures like a tennis court, 21 meters long by 14 wide) is almost twice as large as Hubble (with a length of 13 meters). However, although it may seem otherwise, it weighs half that of its predecessor.

Field of view

Webb’s field of view will be significantly larger than that of Hubble’s camera, although both are smaller than we think. ‘Compared to the diameter of the Moon, a typical (individual) image of the Webb would be roughly 7 to 15 times smaller. The spectral data, where the light is decomposed, cover a much smaller region of the sky ”, says García Marín. This is why most of the images, both from Hubble and future ones from Webb, are compositions of multiple snapshots. Furthermore, the resolution of the new telescope will be significantly higher than that of Hubble. Even that of the Spitzer infrared space telescope.

Infrared VS. optical and ultraviolet wavelengths

Webb will mainly observe the universe in the infrared spectrum, while Hubble sees it mainly in ultraviolet and optical wavelengths. “Thanks to this, Webb will be able to see what happens behind those big clouds of gas and dust where, for example, stars and planets are formed. In addition to this Webb will be able to observe the Universe as it was ago 13.5 billion years1,000 million years older than Hubble. ‘ Because the Webb will come to see the light that emanated from the first moments of the cosmos, to observe the first generation of stars and galaxies.

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On the left, the 'Pillars of Creation' in visible light, and on the right, in infrared.  Note the number of stars that are seen in the infrared
On the left, the ‘Pillars of Creation’ in visible light, and on the right, in infrared. Note the number of stars seen in the infrared – NASA / ESA


Another difference between Hubble and Webb is their position relative to Earth: while the former is about 600 kilometers above our heads, the new space telescope will be at 1.6 million kilometers, at the point named as Lagrange 2.

Possibility of repair

Being much further from home means that it will be much more difficult to repair. In fact, a priori human missions are ruled out to fix possible failures, contrary to what happens with Hubble. This is why, in part, their launch has been delayed so long in recent years, as instruments had to be ‘thoroughly’ tested to have the minimum margin of failure.

Useful life

Although it is still too early to compare, it is expected that James Webb will not be as long-lived as Hubble. In the words of García Marín: «The Webb has a life requirement of five years. We hope it lasts 10 or more. It probably won’t last as long as Hubble, but I hope it does! “

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