The primary difference between Webb and Herschel is wavelength range: Webb goes from 0.6 to 28.5 microns Herschel went from 60 to 500 microns. The Herschel Space Observatory was an infrared telescope built by the European Space Agency - it too orbited the L2 point (where Webb will be). Image credit: ESA / Herschel / SPIRE / PACS / HELGA ESA / XMM / EPIC / OM Infrared image of the Andromeda Galaxy (M31) taken by Herschel (orange) with an X-ray image from XMM-Newton superposed over it (blue). Infrared telescopes, like Webb, are ideal for observing these early galaxies. This can make distant objects very dim (or invisible) at visible wavelengths of light, because that light reaches us as infrared light. Furthermore, any light in that space will also stretch, shifting that light's wavelength to longer wavelengths. It tells us that the expansion of the universe means it is the space between objects that actually stretches, causing objects (galaxies) to move away from each other. When we talk about the most distant objects, Einstein's General Relativity actually comes into play. The universe (and thus the galaxies in it) is expanding. One reason Webb will be able to see the first galaxies is because it is an infrared telescope. Essentially, Hubble can see the equivalent of 'toddler galaxies' and Webb Telescope will be able to see 'baby galaxies'. This illustration compares various telescopes and how far back they are able to see. Seeing back into the cosmos Credit: NASA and and Ann Feild īecause of the time it takes light to travel, the farther away an object is, the farther back in time we are looking. Read on to explore some of the details of what these While Webb will be 1.5 million kilometers (km) away at the second Lagrange Hubble is in a very close orbit around the earth, Light collecting area means that Webb can peer farther back into time than Webb also has a much bigger mirror than Hubble. Wavelengths (though it has some infrared capability). In the infrared, while Hubble studies it primarily at optical and ultraviolet This is the other reason that Webb is not a replacement for Hubble its capabilities are not identical. Thus observations of these distant objects (like the first galaxies formed in the Universe, for example) requires an infrared telescope.

In particular, more distant objects are more highly redshifted, and their light is pushed from the UV and optical into the near-infrared. Hubble's science pushed us to look to longer wavelengths to 'go beyond' what Hubble has already done. After all, Webb is the scientific successor to Hubble its science goals were motivated by results from Hubble. Webb often gets called the replacement for Hubble, but we prefer to call it a successor. Livio & Hubble 20th Anniversary Team (STScI) In the infrared image, we can see more stars that weren't visible before. Comparison of the Carina Nebula in visible light (left) and infrared (right), both images by Hubble.

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