<p><a href="https://i.sstatic.net/mKVVi.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/mKVVi.jpg" alt="screenshot from YouTube video &quot;Stars through a telescope 1&quot; https://youtu.be/LdigmkmEjUo" /></a> <a href="https://i.sstatic.net/DRKS4.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/DRKS4.jpg" alt="screenshot from YouTube video &quot;Stars through a telescope 1&quot; https://youtu.be/LdigmkmEjUo" /></a>
<a href="https://i.sstatic.net/aB6qj.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/aB6qj.jpg" alt="screenshot from YouTube video &quot;Stars through a telescope 1&quot; https://youtu.be/LdigmkmEjUo" /></a></p>
<blockquote>
<p>...pulsing bright rainbow of colors...</p>
</blockquote>
<p>Sounds like very bad <a href="https://en.wikipedia.org/wiki/Astronomical_seeing" rel="nofollow noreferrer">astronomical seeing</a> effects. Even a steady atmosphere acts like a weak prism and in fact all dielectrics tend to bend blue light more than red.</p>
<ul>
<li><a href="https://astronomy.stackexchange.com/q/34481/7982">When are wedge prisms used to correct chromatic effects of atmospheric refraction? (atmospheric dispersion)</a></li>
</ul>
<p>Astronomical seeing is basically disordered refraction due to turbulence and it has a chromatic component as well. A bright point-like object seen through thick turbulent air will definitely appear to &quot;twinkle&quot; not only in intensity but in color, since the intensity noise will be different for blue than green or red.</p>
<p>Your Dobsonian has quite a large light collection area so even a random star, not otherwise considered bright, will become extremely bright when viewed through it.</p>
<p>So there's probably nothing amiss with your telescope based on this observation. If you'd like to see the effect reduced, you can move to extended objects (as opposed to unresolved, point-like stars) such as planets and nebulae and even the disk of the moon at very high magnification when it won't be so overwhelmingly bright. Try the terminator; the line between the bright and dark areas of the moon where shadows are long and the 3D nature of the surface is more dramatic.</p>
<p>You can also try:</p>
<ul>
<li>waiting until much later at night when the Earth's surface and atmosphere has cooled a bit and there's less turbulence</li>
<li>looking closer to the zenith where you light path traverses less atmosphere than it would looking closer to the horizon</li>
<li>looking in directions away from any hotter areas like urban centers</li>
<li>if possible, moving your scope to a substantially higher elevation (helps only if the source of the turbulence is local)</li>
</ul>
<hr />
<p><a href="https://i.sstatic.net/dSmJE.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/dSmJE.png" alt="enter image description here" /></a> <a href="https://en.wikipedia.org/wiki/File:Atmos_struct_imaging.svg" rel="nofollow noreferrer">source</a></p>
<hr />
<p>cued at <code>12:23</code> watch for about 30 seconds to see the color <a href="https://aviation.stackexchange.com/q/73020/14213">scintillations</a>.</p>
<p><div class="youtube-embed"><div>
                <iframe width="640px" height="395px" src="https://www.youtube.com/embed/LdigmkmEjUo?start=743"></iframe>
            </div></div></p>

CC BY-SA 4.0
2021-11-22T01:24:46.777Z
Moving the scope to a substantially higher elevation isn't easy in the Netherlands. "The [Vaalserberg](https://en.wikipedia.org/wiki/Vaalserberg) is a mountain with a height of 322.4 metres (1,058 ft) above NAP and is the highest point in the European part of the Netherlands".
PM 2Ring
CC BY-SA 4.0
2021-11-22T02:14:54.257Z
@PM2Ring indeed! While the question addresses the OP directly it is also meant to be helpful to future readers as well ${}^1$; and for some, a vehicle and some mountains might be available. [I've been thinking about](https://chat.stackexchange.com/transcript/message/59320076#59320076) assembling a DIY Dobsonian for myself; I don't have a vehicle but if it's transportable enough (disassembled) that I can bring it on public transportation there are plenty of mountains within reach here. $${}^1 \text{SE is both a floor wax and a desert topping}$$
uhoh
CC BY-SA 4.0
2021-11-22T12:12:39.750Z
In the right conditions, one can see our lovely Sun in the same fashion without any optical equipment : https://en.wikipedia.org/wiki/Green_flash
fraxinus
CC BY-SA 4.0
2021-11-22T14:21:32.853Z
Also, collimation could help, as well as simply letting the air column inside the telescope cool down, far away from hot air flowing out of indoor rooms.
Eric Duminil
CC BY-SA 4.0
2021-11-21T23:27:07.647Z
2021-11-22T20:12:10.607Z
2021-11-22T20:12:10.607Z
uhoh
<p>My husband and I are complete amateurs. Tonight was only our second night using our new Orion XT6 <a href="https://en.wikipedia.org/wiki/Dobsonian_telescope" rel="nofollow noreferrer">Dobsonian telescope</a>. <a href="https://en.wikipedia.org/wiki/Betelgeuse" rel="nofollow noreferrer">Betelgeuse</a> looked very clear, bright red. However, when we pointed the telescope at it, it appeared in a pulsing bright rainbow of colors.</p>
<p>What did we see? Our telescope is a reflecting telescope, so we didn't expect <a href="https://en.wikipedia.org/wiki/Chromatic_aberration" rel="nofollow noreferrer">chromatic abberation</a>. Did we manage to see the rainbow nebula around Betelgeuse? Or, did this have something to do with light pollution, which was pretty bad in that part of the sky?</p>
<p>Location: the Netherlands</p>
<p>Telescope: 6&quot; Dobsonian, 25 mm eye piece</p>

CC BY-SA 4.0
2021-11-22T16:52:15.030Z
Re *"Tonight"*: What was the exact time? And the approximate [latitude](https://en.wikipedia.org/wiki/Latitude) and [longitude](https://en.wikipedia.org/wiki/Longitude) (within 1° or so).  (From this, the altitude of Betelgeuse can be computed.) The highest possible altitude of Betelgeuse is approx. 45° ((90° - [52°](https://en.wikipedia.org/wiki/Amsterdam)) + [7°](https://en.wikipedia.org/wiki/Betelgeuse)).
Peter Mortensen
<amateur-observing><newtonian-telescope><betelgeuse>
Betelgeuse appears in a rainbow of colors through a Newtonian telescope
Dhara
# Betelgeuse appears in a rainbow of colors through a Newtonian telescope

(Asked by: username_0 on 2021-11-21)

My husband and I are complete amateurs. Tonight was only our second night using our new Orion XT6 [Dobsonian telescope](https://en.wikipedia.org/wiki/Dobsonian_telescope). [Betelgeuse](https://en.wikipedia.org/wiki/Betelgeuse) looked very clear, bright red. However, when we pointed the telescope at it, it appeared in a pulsing bright rainbow of colors.

What did we see? Our telescope is a reflecting telescope, so we didn't expect [chromatic abberation](https://en.wikipedia.org/wiki/Chromatic_aberration). Did we manage to see the rainbow nebula around Betelgeuse? Or, did this have something to do with light pollution, which was pretty bad in that part of the sky?

Location: the Netherlands

Telescope: 6" Dobsonian, 25 mm eye piece

**Tags:** amateur-observing, newtonian-telescope, betelgeuse

> **Comments:**
> **username_1**: Re *"Tonight"*: What was the exact time? And the approximate [latitude](https://en.wikipedia.org/wiki/Latitude) and [longitude](https://en.wikipedia.org/wiki/Longitude) (within 1° or so).  (From this, the altitude of Betelgeuse can be computed.) The highest possible altitude of Betelgeuse is approx. 45° ((90° - [52°](https://en.wikipedia.org/wiki/Amsterdam)) + [7°](https://en.wikipedia.org/wiki/Betelgeuse)).  

---

## 1 answers

### Answer by username_2 on 2021-11-21. Score: 9 | Accepted answer

[![screenshot from YouTube video ](https://i.sstatic.net/mKVVi.jpg)](https://i.sstatic.net/mKVVi.jpg) [![screenshot from YouTube video ](https://i.sstatic.net/DRKS4.jpg)](https://i.sstatic.net/DRKS4.jpg)
[![screenshot from YouTube video ](https://i.sstatic.net/aB6qj.jpg)](https://i.sstatic.net/aB6qj.jpg)

> ...pulsing bright rainbow of colors...

Sounds like very bad [astronomical seeing](https://en.wikipedia.org/wiki/Astronomical_seeing) effects. Even a steady atmosphere acts like a weak prism and in fact all dielectrics tend to bend blue light more than red.

* [When are wedge prisms used to correct chromatic effects of atmospheric refraction? (atmospheric dispersion)](https://astronomy.stackexchange.com/q/34481/7982)

Astronomical seeing is basically disordered refraction due to turbulence and it has a chromatic component as well. A bright point-like object seen through thick turbulent air will definitely appear to "twinkle" not only in intensity but in color, since the intensity noise will be different for blue than green or red.

Your Dobsonian has quite a large light collection area so even a random star, not otherwise considered bright, will become extremely bright when viewed through it.

So there's probably nothing amiss with your telescope based on this observation. If you'd like to see the effect reduced, you can move to extended objects (as opposed to unresolved, point-like stars) such as planets and nebulae and even the disk of the moon at very high magnification when it won't be so overwhelmingly bright. Try the terminator; the line between the bright and dark areas of the moon where shadows are long and the 3D nature of the surface is more dramatic.

You can also try:

* waiting until much later at night when the Earth's surface and atmosphere has cooled a bit and there's less turbulence
* looking closer to the zenith where you light path traverses less atmosphere than it would looking closer to the horizon
* looking in directions away from any hotter areas like urban centers
* if possible, moving your scope to a substantially higher elevation (helps only if the source of the turbulence is local)

---

[![enter image description here](https://i.sstatic.net/dSmJE.png)](https://i.sstatic.net/dSmJE.png) [source](https://en.wikipedia.org/wiki/File:Atmos_struct_imaging.svg)

---

cued at `12:23` watch for about 30 seconds to see the color [scintillations](https://aviation.stackexchange.com/q/73020/14213).

> **Comments:**
> **username_3**: Moving the scope to a substantially higher elevation isn't easy in the Netherlands. "The [Vaalserberg](https://en.wikipedia.org/wiki/Vaalserberg) is a mountain with a height of 322.4 metres (1,058 ft) above NAP and is the highest point in the European part of the Netherlands".  
> **username_2**: @PM2Ring indeed! While the question addresses the OP directly it is also meant to be helpful to future readers as well ${}^1$; and for some, a vehicle and some mountains might be available. [I've been thinking about](https://chat.stackexchange.com/transcript/message/59320076#59320076) assembling a DIY Dobsonian for myself; I don't have a vehicle but if it's transportable enough (disassembled) that I can bring it on public transportation there are plenty of mountains within reach here. $${}^1 \text{SE is both a floor wax and a desert topping}$$  
> **username_4**: In the right conditions, one can see our lovely Sun in the same fashion without any optical equipment : https://en.wikipedia.org/wiki/Green_flash  
> **username_5**: Also, collimation could help, as well as simply letting the air column inside the telescope cool down, far away from hot air flowing out of indoor rooms.  

---

