See a comparison of images from Hubble and Webb

It may not seem obvious why astronomers need so many different powerful space telescopes. Is it certain that a more powerful telescope is better than a less powerful one? So why are there several different telescopes in orbit, either around the Earth or around the Sun?

The answer has to do with two main factors. One is the telescope’s field of view, which means how much of the sky it’s looking at. Some telescopes are useful for looking at large areas of the sky in less detail, serving as survey telescopes to pinpoint objects for further investigation or to look at the universe on a large scale — like the recently launched Euclid mission. Others, like the Hubble Space Telescope, look at small regions of the sky in great detail, which is useful for studying specific objects.

Another important factor for space telescopes is the wavelength in which they operate. Both Hubble and the James Webb Space Telescope are used to study objects like galaxies, but they do so at different wavelengths. Hubble operates primarily in the visible wavelength of light, like human eyes, while Webb operates in the infrared. This means that they can see different sides of the same things.

To illustrate how this works in practice, a new comparison shows the same target, galaxy NCG 3256, as seen by both Webb and Hubble.

Strange galaxy NGC 3256 dominates this image from the NASA/ESA/CSA James Webb Space Telescope. Located about 120 million light-years away in the constellation Phella, this Milky Way-sized galaxy is a resident of the Hydra-Centaurus Supercluster. ESA/Webb, NASA & CSA, L. Armus, A. Evans

This web image shows the tendrils of dust and gas that make up the arms of this galaxy. When new young stars are born out of dust and gas, they release radiation that strikes the dust grains around them, making that dust glow in infrared. Young stars also shine brightly in the infrared wavelength, with the brightest regions indicating hotbeds of star formation.

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Strange galaxy NGC 3256 takes center stage in this image from the NASA/ESA Hubble Space Telescope. This distorted galaxy is the wreckage of a head-on collision between two spiral galaxies that likely occurred 500 million years ago, and is filled with clumps of young stars formed as a result of the collision of gas and dust from the two galaxies. European Space Agency/Hubble, NASA

The Hubble image shows the same galaxy but seen at a different wavelength, originally taken in 2018. While Webb’s infrared vision allows looking through clouds of dust, in the visible light range that Hubble works in the dust creates dark filaments that block out the light. The galaxy is much brighter in the infrared than in the visible wavelength, but at this range you can see more clearly that the galaxy actually has two centers, or nuclei, the result of two galaxies merging together.

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