<p>These are not JWST images. The website shows you where JWST is pointing overlaid onto an existing older all-sky image. (Notice how you can zoom out and look over the whole sky.)</p>
<p>In this case the &quot;<a href="https://en.wikipedia.org/wiki/2MASS" rel="noreferrer">Two Micron All Sky Survey (2MASS)</a>&quot;, which imaged the whole sky in infra-red some 20yrs ago, was chosen. They did their survey with ground-based telescopes over many year with varying levels of background light (specifically airglow). The image you see in the JWST webpage is the product of stitching these millions of images together to form a complete mosaic. This can leave artifacts as one image can be more noisy or have a higher background then the one next to it. A stripe-like pattern can then show e.g. gaps between images or the stripe-like observation pattern.
See the <a href="https://irsa.ipac.caltech.edu/Missions/2MASS/docs/sixdeg/" rel="noreferrer">2MASS website</a> for some more information, which is also the source for the image below.</p>
<p><a href="https://i.sstatic.net/H3XDefpO.png" rel="noreferrer"><img src="https://i.sstatic.net/H3XDefpO.png" alt="enter image description here" /></a></p>
<p>You might find it also interesting to look at other sky-surveys that sometimes show similar artifacts <a href="https://aladin.cds.unistra.fr/AladinLite/" rel="noreferrer">here</a>.</p>
<p>This has nothing to do with JWST.</p>

CC BY-SA 4.0
2024-04-25T22:12:58.690Z
Do you think we can suppose that since there is expected to be [higher limiting magnitudes](https://www.ipac.caltech.edu/2mass/overview/about2mass.html) for the "red" channel (Ks, 2.17 um) than for the "green" (H, 1.65 um) and "blue" (J, 1.25 um) channels that the noise, when visible is always going to appear first in red as shown in the question?
uhoh
CC BY-SA 4.0
2024-04-26T20:55:11.903Z
@uhoh --- I think this is right, if you mean that the noise level is higher (in data units not magnitude units). 

Presumably the sky-survey images show (I - BG), where I is the observed data, BG is the sky background in each frame (variable, as in SpaceCore's pic). The black level in the display image should be (X * N), with N = the noise, and N = (BG)^0.5 neglecting readnoise etc. So visible noise means (X * N) is too small, either because X was not chosen well, N was underestimated, or maybe because BG varied across the survey tile?
giardia
CC BY-SA 4.0
2024-04-24T23:56:26.327Z
2024-04-24T23:56:26.327Z
SpaceCore
<p>The current image <a href="https://spacetelescopelive.org/webb" rel="nofollow noreferrer">here</a> has what seem to be periodic bands across the image made up of red dots.  What are these?
<a href="https://i.sstatic.net/Dd7apuP4.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/Dd7apuP4.jpg" alt="scaled-down version of a screenshot" /></a></p>

<james-webb-space-telescope>
What are these bands of dots on this Webb space telescope image?
Ken - Enough about Monica
# What are these bands of dots on this Webb space telescope image?

(Asked by: username_0 on 2024-04-24)

The current image [here](https://spacetelescopelive.org/webb) has what seem to be periodic bands across the image made up of red dots. What are these?
[![scaled-down version of a screenshot](https://i.sstatic.net/Dd7apuP4.jpg)](https://i.sstatic.net/Dd7apuP4.jpg)

**Tags:** james-webb-space-telescope


---

## 1 answers

### Answer by username_1 on 2024-04-24. Score: 9 | Accepted answer

These are not JWST images. The website shows you where JWST is pointing overlaid onto an existing older all-sky image. (Notice how you can zoom out and look over the whole sky.)

In this case the "[Two Micron All Sky Survey (2MASS)](https://en.wikipedia.org/wiki/2MASS)", which imaged the whole sky in infra-red some 20yrs ago, was chosen. They did their survey with ground-based telescopes over many year with varying levels of background light (specifically airglow). The image you see in the JWST webpage is the product of stitching these millions of images together to form a complete mosaic. This can leave artifacts as one image can be more noisy or have a higher background then the one next to it. A stripe-like pattern can then show e.g. gaps between images or the stripe-like observation pattern.
See the [2MASS website](https://irsa.ipac.caltech.edu/Missions/2MASS/docs/sixdeg/) for some more information, which is also the source for the image below.

[![enter image description here](https://i.sstatic.net/H3XDefpO.png)](https://i.sstatic.net/H3XDefpO.png)

You might find it also interesting to look at other sky-surveys that sometimes show similar artifacts [here](https://aladin.cds.unistra.fr/AladinLite/).

This has nothing to do with JWST.

> **Comments:**
> **username_2**: Do you think we can suppose that since there is expected to be [higher limiting magnitudes](https://www.ipac.caltech.edu/2mass/overview/about2mass.html) for the "red" channel (Ks, 2.17 um) than for the "green" (H, 1.65 um) and "blue" (J, 1.25 um) channels that the noise, when visible is always going to appear first in red as shown in the question?  
> **username_3**: @username_2 --- I think this is right, if you mean that the noise level is higher (in data units not magnitude units).   Presumably the sky-survey images show (I - BG), where I is the observed data, BG is the sky background in each frame (variable, as in username_1's pic). The black level in the display image should be (X * N), with N = the noise, and N = (BG)^0.5 neglecting readnoise etc. So visible noise means (X * N) is too small, either because X was not chosen well, N was underestimated, or maybe because BG varied across the survey tile?  

---

