Atmospheric optical phenomena

[Listener]

Dunno - but I'll try and think it through ...

We all know the sky turns red in the West in the evening when the weather is set fair for the following day and if the Eastern sky is red in the morning it looks bad for the coming weather.

It's to do with refraction of the light so that we are seeing the red end of a specrum when the sky is red - high pressure in the West or damp air in the East.

If the sky is red in the early evening it seems to be neither of these two - but some atmospheric condition or other is showing you a sky lit by the red end of the rainbow.

Guess you knew that

[Radathser]

I did, but that might be the middle man mumble jumble I need for someone who can explain it to explain it.

Thanks, Listener, don't beat yourself up, heh.

[ceptimus]

I'll have a shot at an explanation, but it may be a bit long-winded. Scroll down to the end for my guess as to what happened the day you and your friend witnessed it.

The reason we get red skies mornings and evenings is that the sunlight that reaches us then is passing through many miles of atmosphere.

The main part of the atmosphere, where the air is thick and almost all weather happens is only about ten miles deep. So if the sun is overhead, the light is passing through about ten miles of air to reach us.

But when the sun is low the light still has to do the ten vertical miles plus maybe fifty or more miles horizontally.

The atmosphere scatters the shorter wavelength (blue) light more than the longer wavelength (red). So the blue light gets smeared all over the sky (this is the simple explanation of why the sky is blue). This leaves the direct light from the sun missing some of its blue light, so the sun appears redder than it would if you viewed it from space. The more air the sunlight passes through, the redder it gets.

Now any dust, smoke, or other particles in the atmosphere enhance the effect - so we get spectacular sunsets for a few months after a big volcanic eruption due to the smoke from the volcano in the high atmosphere.

When the air is 'dusty' like this, most of the blue light has been scattered long before the light reaches us, and then the red part begins to scatter too, turning the whole sky red.

My guess is that on the day you witnessed the spectacular reddening, there was a layer of dirty air close to the ground, capped by upper clearer air. The dirty air could be caused by a fire - maybe a forest fire - or even just lots of pollen from trees, grasses or grain crops if it was hay fever season. The 'capped layer' of air is often caused when there is a temperature inversion in the atmosphere.

As the sun moved lower in the sky it would fairly quickly encounter a lot more of the dirty air in reaching you. And hence the sudden reddening. The effect would be most pronounced if the 'dirt' didn't exist immediately above you. If there were forest fires or pollen plumes in the direction of the sun this could happen.

[Radathser]

Well done, Ceptimus.

In retrospect, the event my friend and I witnessed happened around mid to late May. Now, I live East of the Great Dismal Swamp, and just 30 miles North of the North Carolina border. Ever since Early June and late May we've been having smoke problems from North Carolina, and more recently, the Great Dismal swamp due to large forest fires in Carolina and peat fires in the Dismal Swamp. What we may have witness could have been just before the smoke, "fell," to Earth and soon after the fires began. So Ceptimus, yes, you have quite a solid theory in my humble opinion on what happened. You could be wrong, but I think the margin for error on your part is probably pretty small.

The Smoke problem throughout June has been so bad that all of my cloths, and all of my friends smell like smoke. None of us are smokers. Visibility is at times worse than fog. While we've had alot of rain in the past few weeks that have temporarily, "put out the fires," it is predicted that unless we're hit by a Tropical Storm or Hurricane, we will likely have a smoke problem until the end of Summer in Late August. This puts a terrible kink in my plans to run a Marathon on Labor Day weekend. While I'm probably fit enough to run my first marathon straight through, I planned to train the entire summer, every day, so that I might have a shot at first place or the top five or top ten. [Something like 80,000$ in prizes, but I'm in it for the charity, for the journey, the breaking of a mental barrier which probably doesn't exist for me, to experience this infamous, "Wall," and for self improvement in general.]

But yes, well played, sir. Thanks, I now have a reasonable explanation for the awesome red skies we witnessed. Other than strange brownies from strangers.

[Ensign Steve]

Parhelic Circle

[Farren]

So I was wondering, can anyone tell me what this is?



Because I'm stumped

[Ensign Steve]

I'm confused. It looks like a cartoon.

[Farren]

[Leesifer]

It looks a bit cheeky to me

[Farren]

An optical illusion caused by the moon behind the clouds, maybe?

[Doctor X]

I gather this explains wind.

--J.D.

[Farren]

BTW JD that parhelic circle pic is stunning

[Ensign Steve]

Originally Posted by Farren

BTW JD that parhelic circle pic is stunning

If you click the "next" arrow, it tells you how it happens.

[Kael]

When I was a kid we saw a single small cloud that was rainbow-colored, but no actual rainbow. What's that called?

[Michali]

Yeah, ceptimus was probably right regarding the red sky phenomenom. My house was at the edge of a forest fire once, and it was mid afternoon, and there is no way to describe how red the skywas. The entire dome of my sky pov was as red as an apple. Not even that evening red, but I mean red.

Anyway, isn't the sky from the pov of Mar's surface actually blue during the day?

[Doctor X]

We have been having problems getting images from our Mars probe. . . .

--J.D.

[cappuccino]

Rome have those deep red early evenings sometimes. I think from the all various types of dust blown in from the Sahara and continental Africa at the peak of the hot windy summer season. I remember as the sun was starting to set, the entire city would be just flooded with redness.

[Ensign Steve]

Todays APOD:

http://antwrp.gsfc.nasa.gov/apod/ap090512.html

Explanation: Why would clouds appear to be different colors? The reason here is that ice crystals in distant cirrus clouds are acting like little floating prisms. Sometimes known as a fire rainbow for its flame-like appearance, a circumhorizon arc lies parallel to the horizon. For a circumhorizontal arc to be visible, the Sun must be at least 58 degrees high in a sky where cirrus clouds are present. Furthermore, the numerous, flat, hexagonal ice-crystals that compose the cirrus cloud must be aligned horizontally to properly refract sunlight in a collectively similar manner. Therefore, circumhorizontal arcs are quite unusual to see. This circumhorizon display was photographed through a polarized lens above Dublin, Ohio last week.

[Ensign Steve]

Three sunrises.



Possible explanation (controversial! ):
APOD: 2009 August 4 - A Triple Sunrise Over Gdansk Bay

[Ensign Steve]

Another one from APOD:

If you tried to enter this hall of fog, you would find it dissipates around you. The hall is actually an optical illusion created by sunlight backscattering off of a cloud passing below the peak of the mountain from which this picture was taken. Known as "the glory", the phenomenon is frequently seen from airplanes. The ring's center is not visible, but if it were, the shadow of the observer would appear. This shadow would likely change as clouds passed, creating a faux moving giant known as the Brocken Spectre. In the picture, several concentric rings of the glory appear to create a hall for this mountain king. The cause of the glory has only been understood recently and is relatively complex. Briefly, small droplets of water reflect, refract, and diffract sunlight backwards towards the Sun. The phenomenon has a counterpart in astronomy, where looking out from planet Earth in the direction opposite the Sun yields a bright spot called the gegenschein.

http://antwrp.gsfc.nasa.gov/apod/ap100504.html

[ceptimus]

Circumzenithal arc photographed by Andrew G. Saffas in Concord, California.

[Dingfod]

Once I saw both one of those and a regular rainbow at the same time while riding my motorcycle back from Colorado. The sky was mostly clear, but there was one cloud that rain was falling from off to the east, in its rain I saw the rainbow. Above me, but partially obscured by the uppermost part of the rain cloud, was the circumzenithal arc, or upside-down rainbow as I called it. I wish I had a camera with me when I saw it.

[irukandji]

this winter i saw a complete 22° halo around the sun....
i had seen same around the moon many times but this
was a first... i was by the bay walking the dogs and it
was such an amazing experience i was looking around
for someone to share it with... where the heck is an
ice fisherman when ya need one?

lovely pics, folks

[roastelk]

sun dogs and halos are pretty common up here in the winter months, more so in extreem cold.....-40.


heres a couple photos of a sunset i took on my flight out of montego bay 2 weeks ago. some where between sea level and 36000 feet.

[Jug Pilot]

Next time you fly, look for this. Subsonic airliners do have supersonic flow on them and if you know where to look you can see the shock wave. Generally, cruise at high altitude if the best place.

YouTube- Standing Normal Shockwave on a 757 wing

If you are looking down the wing it can appear as a vertical curved line.

YouTube- Shockwave over 747 wing

Of course watching the big furry guy playing with it is cool too, but I guess we'll leave that for another thread.