<p>This is because of something called the Doppler effect. As something moves away from us, the Electromagnetic waves it releases will have a longer wavelength.</p>

<p><img src="https://upload.wikimedia.org/wikipedia/commons/thumb/e/e4/Redshift_blueshift.svg/2000px-Redshift_blueshift.svg.png" alt="Look at the Star that is moving away"></p>

<p>Also, because of Hubble's law, galaxies that are further away have an increased velocity, making the red shift even more pronounced.</p>

CC BY-SA 3.0
2015-03-31T21:49:20.047Z
Actually, it's not really the Doppler effect, as the galaxies lie approximately still in space. But you're right about Hubble's law, which describes the expansion of space.
pela
CC BY-SA 3.0
2015-03-31T21:54:02.327Z
So there is a difference between something like cosmological redshift and  nearby objects that exhibit a local Doppler-effect redshift?
theVerma
CC BY-SA 3.0
2015-03-31T21:54:06.310Z
@pela, why it's not the Doppler effect? After all, all the galaxies are moving away from us. So why can't you account for Doppler effect in this case?
aloha
CC BY-SA 3.0
2015-03-31T21:59:02.173Z
@po6 I think this animation will explain the difference. http://webbtelescope.org/webb_telescope/science_on_the_edge/cosmological_redshift.php
theVerma
CC BY-SA 3.0
2015-03-31T22:05:25.607Z
@po6: It's because the Doppler effect arises when observing light emitted from an object moving though space away from or towards us. But the galaxies don't move through space (well, they do move a little, but that's a minor effect). If you calculate the wavelength of observed photons emitted from a distant galaxy in a hypothetical universe that is static when they are emitted, then at some point expands for a while, and then stops before we observe, you will also see that they are redshifted, even though the emitting galaxy were stationary wrt. us both at the time of emission and observation.
pela
CC BY-SA 3.0
2015-04-01T23:18:21.327Z
I agree with pela here. Cosmological redshift and Doppler shift are quite distinct from one another. Special relativity says that redshift tends to infinity as the relative velocity between two objects approaches the speed of light. A finite redshift means a recession velocity less than that of the speed of light. In general relativity, that's not the case. In the ΛCDM model, all objects we see with a redshift of 1.5 or more not only are currently receding from us  at a superluminal velocity, they were doing so when the light we see now was original emitted.
David Hammen
CC BY-SA 3.0
2015-03-31T21:47:02.833Z
2015-03-31T21:47:02.833Z
2017-03-10T09:42:47.390Z
theVerma
<p>Yes.</p>
<p>When light moves through the expanding space, it loses energy and becomes redshifted. As galaxies form, they usually undergo intense starbursts which emit lots of visible and ultraviolet light. In fact, the most distant galaxies — and hence the ones we see farthest back in time — are often detected from their emission at the so-called Lyman <span class="math-container">$\alpha$</span> light, which has a wavelength of 1216 Å.</p>
<p>Galaxies began forming just a few hundred million years after the Big Bang. Since then, the Universe has a expanded by more than a factor of 10 in all directions. The wavelength of the light expands by the same factor, and thus a Lyman <span class="math-container">$\alpha$</span> photon emitted in this epoch today has a wavelength of <span class="math-container">$\sim12,000$</span> Å, or 1.2 <span class="math-container">$\mu$</span>m, which is in the infrared.</p>

CC BY-SA 4.0
2015-03-31T21:47:32.280Z
2021-12-27T10:40:34.657Z
2021-12-27T10:40:34.657Z
pela
<p>I was reading an article that explains why JWST is a successor to Hubble and not a replacement for Hubble. They explained that Hubble's science pushed astronomers to look at longer wavelength. And then they said:    </p>

<blockquote>
  <p>In particular, more distant objects are more highly redshifted, and their light is pushed from the UV and optical into the near-infrared.</p>
</blockquote>

<p>So basically to observe the first galaxies, astronomers have to observe in infrared. My question is why distant objects require observations in the infrared? </p>

<p>Is it because they are at a very large distance from us, so the light has lost a lot of energy on its way so it's detectable in the infrared? </p>

<observational-astronomy><distances><hubble-telescope>
Why are distant objects observed in the near infrared?
aloha
# Why are distant objects observed in the near infrared?

(Asked by: username_0 on 2015-03-31)

I was reading an article that explains why JWST is a successor to Hubble and not a replacement for Hubble. They explained that Hubble's science pushed astronomers to look at longer wavelength. And then they said:

> In particular, more distant objects are more highly redshifted, and their light is pushed from the UV and optical into the near-infrared.

So basically to observe the first galaxies, astronomers have to observe in infrared. My question is why distant objects require observations in the infrared?

Is it because they are at a very large distance from us, so the light has lost a lot of energy on its way so it's detectable in the infrared?

**Tags:** observational-astronomy, distances, hubble-telescope


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## 2 answers

### Answer by username_2 on 2015-03-31. Score: 6 | Accepted answer

Yes.

When light moves through the expanding space, it loses energy and becomes redshifted. As galaxies form, they usually undergo intense starbursts which emit lots of visible and ultraviolet light. In fact, the most distant galaxies — and hence the ones we see farthest back in time — are often detected from their emission at the so-called Lyman $\alpha$ light, which has a wavelength of 1216 Å.

Galaxies began forming just a few hundred million years after the Big Bang. Since then, the Universe has a expanded by more than a factor of 10 in all directions. The wavelength of the light expands by the same factor, and thus a Lyman $\alpha$ photon emitted in this epoch today has a wavelength of $\sim12,000$ Å, or 1.2 $\mu$m, which is in the infrared.


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### Answer by username_1 on 2015-03-31. Score: 2

This is because of something called the Doppler effect. As something moves away from us, the Electromagnetic waves it releases will have a longer wavelength.

![Look at the Star that is moving away](https://upload.wikimedia.org/wikipedia/commons/thumb/e/e4/Redshift_blueshift.svg/2000px-Redshift_blueshift.svg.png)

Also, because of Hubble's law, galaxies that are further away have an increased velocity, making the red shift even more pronounced.

> **Comments:**
> **username_2**: Actually, it's not really the Doppler effect, as the galaxies lie approximately still in space. But you're right about Hubble's law, which describes the expansion of space.  
> **username_1**: So there is a difference between something like cosmological redshift and  nearby objects that exhibit a local Doppler-effect redshift?  
> **username_0**: @username_2, why it's not the Doppler effect? After all, all the galaxies are moving away from us. So why can't you account for Doppler effect in this case?  
> **username_1**: @po6 I think this animation will explain the difference. http://webbtelescope.org/webb_telescope/science_on_the_edge/cosmological_redshift.php  
> **username_2**: @po6: It's because the Doppler effect arises when observing light emitted from an object moving though space away from or towards us. But the galaxies don't move through space (well, they do move a little, but that's a minor effect). If you calculate the wavelength of observed photons emitted from a distant galaxy in a hypothetical universe that is static when they are emitted, then at some point expands for a while, and then stops before we observe, you will also see that they are redshifted, even though the emitting galaxy were stationary wrt. us both at the time of emission and observation.  
> **username_3**: I agree with username_2 here. Cosmological redshift and Doppler shift are quite distinct from one another. Special relativity says that redshift tends to infinity as the relative velocity between two objects approaches the speed of light. A finite redshift means a recession velocity less than that of the speed of light. In general relativity, that's not the case. In the ΛCDM model, all objects we see with a redshift of 1.5 or more not only are currently receding from us  at a superluminal velocity, they were doing so when the light we see now was original emitted.  

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