Iridescent Cloud - astronomy connection? (APOD 25 Nov 2007)

[adrianxw]

Another fine picture but again, where is the astronomical connection. It is a weather picture here on Earth.

[craterchains]

Here, again, is the double standard. We are supposed to keep to astronomy topics and here is a picture about atmospherics?!?!?

[aunt maggie]

I have noticed that these "rare" clouds have only become more common with the increase of air traffic over the years. Can it be that the "iridescence" comes more from gas and oil droplets than just water droplets? I notice also that the cloud iridescence is more like the iridescence you might see at a gas station where oil or gas has been spilled, and not so much the coloring that comes with rainbows. Yet most every site contributes this phenomenon to water droplets.

In other words, could all this "iridescence" be from pollution in our skies rather than mere water droplets?

[Case]

I have noticed that these "rare" clouds have only become more common with the increase of air traffic over the years.

The burning of jet fuel will release water into the air as one of its high percentage remaining products from the chemical reaction. The increase of air traffic has resulted in more "thinner clouds" of water droplets.
The rainbow-color-showing reflective properties of an oily surface are totally different from refractive properties of airborne water droplets, despite their optical similarities.

[auroradude]

Is that Venus I see just above the block wall towards the top right?

[rigelan]

I bet its a piece of dust, not Venus.

[Case]

Is that Venus I see just above the block wall towards the top right?

When you take the timestamp from the Exif, the Sun and Venus should be 45° apart in the sky. The image FOV isn't very obvious, but I think the white dot is much less than 45° from the Sun. Also, the stone wall is much too sharp for Venus to be sharp in the picture. My guess is that the white dot is an image artifact.

[moopst]

I've seen iridescent clouds myself a few times here in Colorado. Often the Front Range mountains will have lenticular clouds which form when the air flowing from the west goes up then down over a mountain. These probably have the uniform water droplets and thin size that favor iridescent clouds.

[BMAONE23]

Is that Venus I see just above the block wall towards the top right?

There are several other "white dots" in the image (right around the apparent solar limb). But I believe that this particular one is right were Mercury should appear to be though it should be too washed out to be visible.

[auroradude]

Yea, I now spotted other image artifacts as well.

Given the subject of very bright clouds near the sun, I realize that the exposure would have to be very short and at a small f/stop. My guess would be approximately 1/250 second at f/22 and 100 iso. It would not be enough exposure for Mercury and Venus would most likely be out of the image given its angular distance from the sun (unless this is a very wide-angle shot).

So, the white spots are most likely just hot pixels since I assume, from the vividness and bleeding of the colors, this was a digital shot.

[iamlucky13]

Another fine picture but again, where is the astronomical connection. It is a weather picture here on Earth.

I've always considered sunlight effects to be astronomical because, well, the sun is a star.

I have noticed that these "rare" clouds have only become more common with the increase of air traffic over the years.

Possibly, as Case explained. Aircraft exhaust does increase the occurence of thin clouds. It's also possible the perceived frequency is falsely inflated by improved communications that allow these pictures to be seen by more people, or simply you noticing them more as you learn more about the effect.

I also want to add on that modern aircraft engines burn extremely clean. There is basically no unburned fuel in the exhaust, and the little bit of pollution that is present is primarily particulates (soot), rather than anything resembling oil.