<blockquote>
<p>Why are these patterns of scattered sunlight aligned to the local horizontal and vertical directions?</p>
</blockquote>
<p>The answer can be found in The New York Times article <a href="https://www.nytimes.com/2017/01/06/science/light-pillars.html" rel="nofollow noreferrer">Light Pillars, a Million-Mirror Optical Illusion on Winter Nights</a> and in The Washington Post's <a href="https://www.washingtonpost.com/weather/2018/12/10/rare-light-pillars-cast-colorful-columns-into-wisconsins-night-sky/" rel="nofollow noreferrer">Rare light pillars cast colorful columns into Wisconsin’s night sky</a> says:</p>
<blockquote>
<p>However, that’s just half the story. The formation of light pillars requires hexagonally shaped ice crystals in the air to reflect the light. Moreover, they have to be oriented horizontally, like flying discs or plates to bounce light back toward the observer. Less-organized orientations can produce sun pillars and halos.</p>
</blockquote>
<p>A more physics-based explanation can be found in <a href="https://earthscience.stackexchange.com/a/10606/6031">this answer</a> to the question <em>Are there measurements or calculations that suggest atmospheric ice plates would be horizontal to within 0.1 degrees?</em></p>
<p>also see Les Cowley's Atmospheric Optics page <a href="http://www.atoptics.co.uk/halo/dogfm.htm" rel="nofollow noreferrer">Sundog formation</a></p>
<p><a href="https://i.sstatic.net/1gaBk.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/1gaBk.jpg" alt="enter image description here" /></a></p>
<p><a href="https://i.sstatic.net/m4Ibm.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/m4Ibm.jpg" alt="enter image description here" /></a></p>
<p>Also from <a href="https://twitter.com/TomPurdyWI/status/1071946562144796672" rel="nofollow noreferrer">this tweet</a>:</p>
<p><a href="https://i.sstatic.net/s4kyU.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/s4kyU.jpg" alt="enter image description here" /></a></p>

CC BY-SA 4.0
2018-12-17T05:35:43.797Z
2020-06-28T02:45:02.513Z
2020-06-28T02:45:02.513Z
uhoh
<p>Note: All of the links in this answer point to various parts of Les Cowley's excellent <a href="https://www.atoptics.co.uk" rel="noreferrer">Atmospheric Optics</a> site. Les combines photographs, simulated images, and descriptions of the underlying physics to beautifully portray and explain a number of different optical effects in our atmosphere.</p>

<p>Note: The imagery on that site is copyrighted. Please do not edit this answer to portray images from that site.</p>

<hr>

<p>That's a very nice picture that shows a number of <a href="https://www.atoptics.co.uk/halosim.htm" rel="noreferrer">ice halos</a>. Ice crystal halos are caused by various shapes of ice crystals. Some of these halos such as the small circle that encircles the Sun in the image in the question are easily seen at all latitudes. Others only appear in very high latitudes, and even there they are rather infrequent.</p>

<p>The small circle is the <a href="https://www.atoptics.co.uk/halo/circular.htm" rel="noreferrer">22° halo</a>. This is a frequently seen halo, much more common than rainbows. It's caused by poorly aligned hexagonal prism ice crystals. If you look closely, you'll see that the sky is darker inside the 22° halo. This is similar to how the sky is darker outside the primary bow of a rainbow. Unlike a rainbow, the color separation is very small, making the 22° halo white rather than colored. If you look closely, you can see that the inner edge has a bit of a reddish tinge.</p>

<p>The two bright spots on the sides of the 22° halo are <a href="https://www.atoptics.co.uk/halo/parhelia.htm" rel="noreferrer">sun dogs</a>. These result from hexagonal plates of ice with their large faces nearly horizontal. The curve the intersects the Sun, runs parallel to the horizon, and intersects the 22° halo at the sun dogs is the <a href="https://www.atoptics.co.uk/halo/pclow.htm" rel="noreferrer">parhelic circle</a>. Parhelic circles result from sunlight reflecting off nearly vertical faces of ice crystals. The mustache atop the 22° halo is the <a href="https://www.atoptics.co.uk/halo/column.htm" rel="noreferrer">upper tangent arc</a>. Tangent arcs result from ice crystals that form hexagonal columns rather than hexagonal plates. As is the case with the 22° halo, sun dogs, parhelic circles, and tangent arcs are fairly common.</p>

<p>The partial circle outside the 22° halo is the not so common <a href="https://www.atoptics.co.uk/halo/supinf.htm" rel="noreferrer">supralateral arc</a>, or possibly the even rarer <a href="https://www.atoptics.co.uk/halo/46hal.htm" rel="noreferrer">46° halo</a>. Atop that is the <a href="https://www.atoptics.co.uk/halo/cza.htm" rel="noreferrer">circumzenithal arc</a>.</p>

CC BY-SA 4.0
2018-06-18T12:12:30.650Z
At night you can see similar, but dimmer effects from a bright moon.  If you know your stars well, you can also see 'extra' stars from the sundogs from bright stars.  These are called 'star pups'  I've not seen them.  To notice them you would have to really know your night sky.
Sherwood Botsford
CC BY-SA 4.0
2018-06-18T11:04:01.960Z
2018-06-18T11:04:01.960Z
David Hammen
<p>The information discussed in the CleanTechnica article <a href="https://cleantechnica.com/2018/06/16/full-fledged-5-alarm-climate-emergency-in-antarctica/" rel="nofollow noreferrer">Full Fledged 5 Alarm Climate Emergency In Antarctica</a> is certainly disconcerting, but the stock photo of the sky and various atmospheric phenomena of sunlight scattered in the atmosphere is still beautiful. My question is about this photo.</p>

<p>I see two circles around the sun, meaning light is scattered at certain angles ABC where B is the scatterer, A is the Sun, and C is the observer. However there are several features that are oriented with respect to the <em>the local horizontal and vertical</em> as well. For example, a long line extending to the left and right from the Sun parallel to the <em>horizon</em> with bright spots where it intersects the inner ring, and the beginnings of arcs, tangent to the <em>tops</em> of the circles but curving <em>vertically upward</em>.</p>

<p><strong>Question:</strong> Why are these patterns of scattered sunlight aligned to the local horizontal and vertical directions?</p>

<p><a href="https://i.sstatic.net/v0fpX.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/v0fpX.jpg" alt="Scattered sunlight pattern on a cold day"></a></p>

CC BY-SA 4.0
2018-06-18T08:08:22.480Z
it is called bisol and is created by flat icecrystals in the air.one have to be at the right place at the right time to see it.
trond hansen
CC BY-SA 4.0
2018-12-17T05:28:36.567Z
Possible duplicate of [Are there measurements or calculations that suggest atmospheric ice plates would be horizontal to within 0.1 degrees?](https://earthscience.stackexchange.com/questions/10436/are-there-measurements-or-calculations-that-suggest-atmospheric-ice-plates-would) It turns out that this was already answered at another question I asked a year and a half ago, related to things seen from space!
uhoh
CC BY-SA 4.0
2018-12-17T06:47:41.753Z
good catch,i have seen it in real life and will never forget how beautiful it was.
trond hansen
CC BY-SA 4.0
2018-12-17T07:12:03.963Z
@trondhansen very nice! I've seen the sun dogs a few times and the inner ring once around 45N but now I'm too close to the equator to see these very often. Instead, during the summer I can see my shadow disappear underneath me at noon.
uhoh
CC BY-SA 4.0
2018-12-21T13:53:32.047Z
It looks like a [solar ice halo](https://apod.nasa.gov/apod/astropix.html)
Fred
CC BY-SA 4.0
2020-06-28T04:28:32.513Z
sorry i used the norwegian name for this the correct name is sundog https://en.wikipedia.org/wiki/Sun_dog
trond hansen
CC BY-SA 4.0
2020-07-02T03:49:29.877Z
@trondhansen I saw it from a ski lift once, it was all around me including below.
Keith McClary
<atmospheric-optics>
Why are these patterns of scattered sunlight aligned to the local horizontal and vertical directions?
uhoh
# Why are these patterns of scattered sunlight aligned to the local horizontal and vertical directions?

(Asked by: username_0 on 2018-06-18)

The information discussed in the CleanTechnica article [Full Fledged 5 Alarm Climate Emergency In Antarctica](https://cleantechnica.com/2018/06/16/full-fledged-5-alarm-climate-emergency-in-antarctica/) is certainly disconcerting, but the stock photo of the sky and various atmospheric phenomena of sunlight scattered in the atmosphere is still beautiful. My question is about this photo.

I see two circles around the sun, meaning light is scattered at certain angles ABC where B is the scatterer, A is the Sun, and C is the observer. However there are several features that are oriented with respect to the *the local horizontal and vertical* as well. For example, a long line extending to the left and right from the Sun parallel to the *horizon* with bright spots where it intersects the inner ring, and the beginnings of arcs, tangent to the *tops* of the circles but curving *vertically upward*.

**Question:** Why are these patterns of scattered sunlight aligned to the local horizontal and vertical directions?

[![Scattered sunlight pattern on a cold day](https://i.sstatic.net/v0fpX.jpg)](https://i.sstatic.net/v0fpX.jpg)

**Tags:** atmospheric-optics

> **Comments:**
> **username_1**: it is called bisol and is created by flat icecrystals in the air.one have to be at the right place at the right time to see it.  
> **username_0**: Possible duplicate of [Are there measurements or calculations that suggest atmospheric ice plates would be horizontal to within 0.1 degrees?](https://earthscience.stackexchange.com/questions/10436/are-there-measurements-or-calculations-that-suggest-atmospheric-ice-plates-would) It turns out that this was already answered at another question I asked a year and a half ago, related to things seen from space!  
> **username_1**: good catch,i have seen it in real life and will never forget how beautiful it was.  
> **username_0**: @username_1 very nice! I've seen the sun dogs a few times and the inner ring once around 45N but now I'm too close to the equator to see these very often. Instead, during the summer I can see my shadow disappear underneath me at noon.  
> **username_2**: It looks like a [solar ice halo](https://apod.nasa.gov/apod/astropix.html)  
> **username_1**: sorry i used the norwegian name for this the correct name is sundog https://en.wikipedia.org/wiki/Sun_dog  
> **username_3**: @username_1 I saw it from a ski lift once, it was all around me including below.  

---

## 2 answers

### Answer by username_4 on 2018-06-18. Score: 6 | Accepted answer

Note: All of the links in this answer point to various parts of Les Cowley's excellent [Atmospheric Optics](https://www.atoptics.co.uk) site. Les combines photographs, simulated images, and descriptions of the underlying physics to beautifully portray and explain a number of different optical effects in our atmosphere.

Note: The imagery on that site is copyrighted. Please do not edit this answer to portray images from that site.

---

That's a very nice picture that shows a number of [ice halos](https://www.atoptics.co.uk/halosim.htm). Ice crystal halos are caused by various shapes of ice crystals. Some of these halos such as the small circle that encircles the Sun in the image in the question are easily seen at all latitudes. Others only appear in very high latitudes, and even there they are rather infrequent.

The small circle is the [22° halo](https://www.atoptics.co.uk/halo/circular.htm). This is a frequently seen halo, much more common than rainbows. It's caused by poorly aligned hexagonal prism ice crystals. If you look closely, you'll see that the sky is darker inside the 22° halo. This is similar to how the sky is darker outside the primary bow of a rainbow. Unlike a rainbow, the color separation is very small, making the 22° halo white rather than colored. If you look closely, you can see that the inner edge has a bit of a reddish tinge.

The two bright spots on the sides of the 22° halo are [sun dogs](https://www.atoptics.co.uk/halo/parhelia.htm). These result from hexagonal plates of ice with their large faces nearly horizontal. The curve the intersects the Sun, runs parallel to the horizon, and intersects the 22° halo at the sun dogs is the [parhelic circle](https://www.atoptics.co.uk/halo/pclow.htm). Parhelic circles result from sunlight reflecting off nearly vertical faces of ice crystals. The mustache atop the 22° halo is the [upper tangent arc](https://www.atoptics.co.uk/halo/column.htm). Tangent arcs result from ice crystals that form hexagonal columns rather than hexagonal plates. As is the case with the 22° halo, sun dogs, parhelic circles, and tangent arcs are fairly common.

The partial circle outside the 22° halo is the not so common [supralateral arc](https://www.atoptics.co.uk/halo/supinf.htm), or possibly the even rarer [46° halo](https://www.atoptics.co.uk/halo/46hal.htm). Atop that is the [circumzenithal arc](https://www.atoptics.co.uk/halo/cza.htm).

> **Comments:**
> **username_5**: At night you can see similar, but dimmer effects from a bright moon.  If you know your stars well, you can also see 'extra' stars from the sundogs from bright stars.  These are called 'star pups'  I've not seen them.  To notice them you would have to really know your night sky.  

---

### Answer by username_0 on 2018-12-17. Score: 2

> Why are these patterns of scattered sunlight aligned to the local horizontal and vertical directions?

The answer can be found in The New York Times article [Light Pillars, a Million-Mirror Optical Illusion on Winter Nights](https://www.nytimes.com/2017/01/06/science/light-pillars.html) and in The Washington Post's [Rare light pillars cast colorful columns into Wisconsin’s night sky](https://www.washingtonpost.com/weather/2018/12/10/rare-light-pillars-cast-colorful-columns-into-wisconsins-night-sky/) says:

> However, that’s just half the story. The formation of light pillars requires hexagonally shaped ice crystals in the air to reflect the light. Moreover, they have to be oriented horizontally, like flying discs or plates to bounce light back toward the observer. Less-organized orientations can produce sun pillars and halos.

A more physics-based explanation can be found in [this answer](https://earthscience.stackexchange.com/a/10606/6031) to the question *Are there measurements or calculations that suggest atmospheric ice plates would be horizontal to within 0.1 degrees?*

also see Les Cowley's Atmospheric Optics page [Sundog formation](http://www.atoptics.co.uk/halo/dogfm.htm)

[![enter image description here](https://i.sstatic.net/1gaBk.jpg)](https://i.sstatic.net/1gaBk.jpg)

[![enter image description here](https://i.sstatic.net/m4Ibm.jpg)](https://i.sstatic.net/m4Ibm.jpg)

Also from [this tweet](https://twitter.com/TomPurdyWI/status/1071946562144796672):

[![enter image description here](https://i.sstatic.net/s4kyU.jpg)](https://i.sstatic.net/s4kyU.jpg)


---

