APOD: Unusual Clouds over Hong Kong (2016 Mar 02)

[APOD Robot]

Unusual Clouds over Hong Kong

Explanation: What's that in the sky? Earlier this month, in the sky high above Hong Kong, China, not just one unusual type of cloud appeared -- but two. In the foreground was a long lenticular cloud, a cloud that forms near mountains from uprising air and might appear to some as an alien spaceship. Higher in the sky, and further in the background, was a colorful iridescent cloud. Iridescent clouds are composed of water droplets of similar size that diffract different colors of sunlight by different amounts. Furthest in the background is the Sun, blocked from direct view by the opaque lenticular, but providing the light for the colors of the iridescent. Either type of cloud is unusual to see in Hong Kong, and unfortunately, after only a few minutes, both were gone.

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[Boomer12k]

Sorry, not really seeing the Lenticular nature of these clouds. Lenticular are "layered and stratified", as is seen in the example link, and as I have seen and recognized personally. I see just smoothness all round here,... Iridescent, that I see...

Can someone show me the lenticular a bit better please?

:---[===] *

[old dude]

Actually, it is quite fortunate that these things last only moments, otherwise they would not have been 'unusual'.

[georgegoad]

Wow, that cloud formation looks so much like the "Martian" spaceships in George Pal's 1953 production of H.G. Wells' "War of the Worlds" it's somewhat uncanny!

[stowaway]

Clouds are not astronomy. This is obviously an inter-stellar spacecraft.

[Chris Peterson]

Sorry, not really seeing the Lenticular nature of these clouds. Lenticular are "layered and stratified", as is seen in the example link, and as I have seen and recognized personally. I see just smoothness all round here,... Iridescent, that I see...

Can someone show me the lenticular a bit better please?

These are probably correctly classified as lenticular clouds, but they're not fully developed, and certainly not very good examples. I've seen clouds like these form into normal lenticular clouds, although they don't always.

[Chris Peterson]

Wow, that cloud formation looks so much like the "Martian" spaceships in George Pal's 1953 production of H.G. Wells' "War of the Worlds" it's somewhat uncanny!

Stupid, credulous people sometimes report such clouds as flying saucers.

[stowaway]

That IS a flying saucer. Are you saying I'm stupid and credulous?

[Nitpicker]

That IS a flying saucer. Are you saying I'm stupid and credulous?

Hardly seems necessary.

[Chris Peterson]

That IS a flying saucer. Are you saying I'm stupid and credulous?

No comment.

[Guest]

If you are going to believe that funny looking clouds have anything to do with astronomy then you may as well believe in flying saucers.

[geckzilla]

If you are going to believe that funny looking clouds have anything to do with astronomy then you may as well believe in flying saucers.

Here's my favorite funny-looking astronomy cloud. https://en.wikipedia.org/wiki/Finger_of_God_(Carina)

[Ann]

If you are going to believe that funny looking clouds have anything to do with astronomy then you may as well believe in flying saucers.

Here's my favorite funny-looking astronomy cloud. https://en.wikipedia.org/wiki/Finger_of_God_(Carina)

keyhole_nebula.jpg

Finger of God? It looks like the f*** finger.

Ann

[Rusty Brown in Cda]

"Opaque" lenticular cloud? I would say "translucent". Cast iron is "opaque".

[P-dub]

Minor lenticular clouds, probably forming by the tall skyscrapers in that city.

That, or Martians are thinking about landing & invading!

[anappleaday]

Is the color from the iridescent cloud from diffraction, as stated, or from refraction, through the water droplets? Thanks.

[neufer]

Is the color from the iridescent cloud from diffraction, as stated,
or from refraction, through the water droplets? Thanks.

[b][color=#0000FF]Interference colors from an oil film on water depend on the thickness of the film. The color seen depends also upon the angle of view.[/color][/b]

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Is the color from an oil film on water
from diffraction, or from reflection

<<The interference colors from an oil film on water can be related to the thickness of the film by using the interference condition and noting that there is a 180 degree phase change upon reflection from the film surface, but no phase change for the reflection from the back surface. This presumes that the index of refraction of the oil is greater than that of the water. The color seen depends also upon the angle of view.>>

<<Iridescent clouds are a diffraction phenomenon caused by small water droplets or small ice crystals individually scattering light. Larger ice crystals produce halos.

If parts of clouds have small droplets or crystals of similar size, their cumulative effect is seen as colors. The cloud must be optically thin, so that most rays encounter only a single droplet. Iridescence is therefore mostly seen at cloud edges or in semi-transparent clouds, and newly forming clouds produce the brightest and most colorful iridescence. When a thin cloud has droplets of similar size over a large extent, the iridescence takes on the structured form of a corona, a central bright disk around the sun or moon surrounded by one or more colored rings. In one instance a lunar corona was observed, with the iridescent cirrus cloud 11–13.6 km above the mean sea level at a temperature of −70 °C. The pure corona was 9.5 km above the mean sea level, at a temperature of −60 °C.>>

[Tekija]

Is the color from the iridescent cloud from diffraction, as stated,
or from refraction, through the water droplets? Thanks.

[b][color=#0000FF]Interference colors from an oil film on water depend on the thickness of the film. The color seen depends also upon the angle of view.[/color][/b]

---

---

Is the color from an oil film on water
from diffraction, or from reflection

<<The interference colors from an oil film on water can be related to the thickness of the film by using the interference condition and noting that there is a 180 degree phase change upon reflection from the film surface, but no phase change for the reflection from the back surface. This presumes that the index of refraction of the oil is greater than that of the water. The color seen depends also upon the angle of view.>>

<<Iridescent clouds are a diffraction phenomenon caused by small water droplets or small ice crystals individually scattering light. Larger ice crystals produce halos.

If parts of clouds have small droplets or crystals of similar size, their cumulative effect is seen as colors. The cloud must be optically thin, so that most rays encounter only a single droplet. Iridescence is therefore mostly seen at cloud edges or in semi-transparent clouds, and newly forming clouds produce the brightest and most colorful iridescence. When a thin cloud has droplets of similar size over a large extent, the iridescence takes on the structured form of a corona, a central bright disk around the sun or moon surrounded by one or more colored rings. In one instance a lunar corona was observed, with the iridescent cirrus cloud 11–13.6 km above the mean sea level at a temperature of −70 °C. The pure corona was 9.5 km above the mean sea level, at a temperature of −60 °C.>>

Iridescent means rainbow-colored and derives from Iris, the Greek goddes that personifies the rainbow and is a messenger of Hera.



"Among their deities, who dwelt on Mt. Olympus, was one called Iris. She was the special messenger of Hera, the Queen Goddess. When Iris carried special messages from Heaven to Earth, she used the rainbows as her pathway."

http://www.historiciris.org/articles/iris-legend.html

[neufer]

Iridescent means rainbow-colored and derives from Iris, the Greek goddes that personifies the rainbow and is a messenger of Hera. "Among their deities, who dwelt on Mt. Olympus, was one called Iris. She was the special messenger of Hera, the Queen Goddess. When Iris carried special messages from Heaven to Earth, she used the rainbows as her pathway."

http://www.historiciris.org/articles/iris-legend.html

<<7 Iris is a large main-belt asteroid orbiting the Sun between Mars and Jupiter. It is the fourth brightest object in the asteroid belt. It is classified as an S-type asteroid, meaning that it has a stony composition. Iris was discovered on August 13, 1847, by J. R. Hind from London. Iris was named after the rainbow goddess Iris in Greek mythology, who was a messenger to the gods, especially Hera. Her quality of attendant of Hera was particularly appropriate to the circumstances of discovery, as she was spotted following 3 Juno by less than an hour of right ascension (Juno is the Roman equivalent of Hera).>>

<<Iridium is a chemical element with symbol Ir and atomic number 77. A very hard, brittle, silvery-white transition metal of the platinum group, iridium is generally credited with being the second densest element (after osmium) based on measured density, although calculations involving the space lattices of the elements show that iridium is denser. It is also the most corrosion-resistant metal, even at temperatures as high as 2000 °C. Although only certain molten salts and halogens are corrosive to solid iridium, finely divided iridium dust is much more reactive and can be flammable.

[b][color=#FF0000]The red arrow points to the Cretaceous–Paleogene boundary.[/color][/b]

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Iridium was discovered in 1803 among insoluble impurities in natural platinum. Smithson Tennant, the primary discoverer, named iridium for the Greek goddess Iris, personification of the rainbow, because of the striking and diverse colors of its salts. Iridium is one of the rarest elements in Earth's crust, with annual production and consumption of only three tonnes.

The Cretaceous–Paleogene boundary of 66 million years ago, marking the temporal border between the Cretaceous and Paleogene periods of geological time, was identified by a thin stratum of iridium-rich clay. A team led by Luis Alvarez proposed in 1980 an extraterrestrial origin for this iridium, attributing it to an asteroid or comet impact. Their theory, known as the Alvarez hypothesis, is now widely accepted to explain the extinction of the non-avian dinosaurs. A large buried impact crater structure with an estimated age of about 66 million years was later identified under what is now the Yucatán Peninsula (the Chicxulub crater).] Dewey M. McLean and others argue that the iridium may have been of volcanic origin instead, because Earth's core is rich in iridium, and active volcanoes such as Piton de la Fournaise, in the island of Réunion, are still releasing iridium.>>

[JayCee]

Wow, that cloud formation looks so much like the "Martian" spaceships in George Pal's 1953 production of H.G. Wells' "War of the Worlds" it's somewhat uncanny!

Good observation. That was my immediate first impression, too. For comparison with today's photo, here is an image from the film, showing the "manta ray" shape of the Martian war machines.

[Smidgen]

Wow, that cloud formation looks so much like the "Martian" spaceships in George Pal's 1953 production of H.G. Wells' "War of the Worlds" it's somewhat uncanny!

Good observation. That was my immediate first impression, too. For comparison with today's photo, here is an image from the film, showing the "manta ray" shape of the Martian war machines.

It also resembles the alien slave drivers' patrol ships in the 1964 film "Robinson Crusoe on Mars"

[DavidLeodis]

I was unable to run the application that was brought up through the "clouds" link in the "Iridescent clouds are composed of" in 2 browsers that I tried, as I got a message stating it was an untrusted application that was blocked by Java Security. I wonder if that is just a problem with Java settings on my computer or was anybody else unable to run the application . As it seems to be a genuine NASA application I assume however that it will be trustworthy if I could run it!

I also have a query about the date when the image was taken. In the explanation it states "Earlier this month" which will be March 1 2016 as the APOD is dated March 2 2016. It does though seem extremely quick to have a non-urgent image used as an APOD the day after it was taken! I wonder therefore if it should state "Earlier in February"?

[aramekar]

With all this talk of iridescence, I want to take a moment to point out the Kelvin–Helmholtz instability towards the bottom center!

The artistic wave like profile is a bit blocked by the cell phone tower but what is interesting is that this instability appears to happen parallel to the ground plane. Normally if you look at images of Kelvin-Helmoltz instabilities in clouds, the wave like pattern 'upright' or on top portion of the cloud (perhaps because it is common to have wind speeds differing vertically with altitude rather than horizontally in space?). I was pleasantly surprised to finally see a picture where the Kelvin Helholtz waves are not on top!

Ana