APOD: Iridescent Clouds over Sweden (2024 Jul 07)

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APOD: Iridescent Clouds over Sweden (2024 Jul 07)

Post by APOD Robot » Sun Jul 07, 2024 4:06 am

Image Iridescent Clouds over Sweden

Explanation: Why are these clouds multi-colored? A relatively rare phenomenon in clouds known as iridescence can bring up unusual colors vividly -- or even a whole spectrum of colors simultaneously. These polar stratospheric clouds also, known as nacreous and mother-of-pearl clouds, are formed of small water droplets of nearly uniform size. When the Sun is in the right position and, typically, hidden from direct view, these thin clouds can be seen significantly diffracting sunlight in a nearly coherent manner, with different colors being deflected by different amounts. Therefore, different colors will come to the observer from slightly different directions. Many clouds start with uniform regions that could show iridescence but quickly become too thick, too mixed, or too angularly far from the Sun to exhibit striking colors. The featured image and an accompanying video were taken late in 2019 over Ostersund, Sweden.

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Re: APOD: Iridescent Clouds over Sweden (2024 Jul 07)

Post by Guest again » Sun Jul 07, 2024 2:17 pm

I live in a north south valley. In March and April this occasionally happens at sunset and outside everything turns red for about 5 minutes. It looks like photos of Mars from one of the rovers. Whenever I observe this it feels so strange that it seems to change the pace of my heart beat. Now I have an explanation why this occurs and can cross it off my bucket list.

zendae
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Re: APOD: Iridescent Clouds over Sweden (2024 Jul 07)

Post by zendae » Sun Jul 07, 2024 3:41 pm

Since today's APOD is an EPOD, here are a couple of photos I took a few days ago. These mammatocumulus appeared after quite a randy storm!
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Ann
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Re: APOD: Iridescent Clouds over Sweden (2024 Jul 07)

Post by Ann » Sun Jul 07, 2024 4:51 pm

zendae wrote: Sun Jul 07, 2024 3:41 pm Since today's APOD is an EPOD, here are a couple of photos I took a few days ago. These mammatocumulus appeared after quite a randy storm!

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Nice pictures, zendae! :D

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Re: APOD: Iridescent Clouds over Sweden (2024 Jul 07)

Post by starsurfer » Sun Jul 07, 2024 10:16 pm

I would love to have my head in those clouds! :D

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Re: APOD: Iridescent Clouds over Sweden (2024 Jul 07)

Post by florid_snow » Mon Jul 08, 2024 12:35 am

If you love clouds and you love astronomy then no matter what condition the sky, you'll enjoy a look up after sunset!



But I also love nitpicking... today's APOD says that iridescent clouds are "relatively rare" but they are actually very common. If there are no clouds, you can't see iridescent clouds, of course, and if the clouds are too thick to see the sun, then you can't see iridescent clouds either. But if you have the conditions where you can both see some clouds and the sun at the same time, and then these clouds are visually near to the sun, you are guaranteed to see iridescence. It always occurs when the edge of a cloud visually approaches the edge of the sun (because the edge of the cloud always has droplets of approximately uniform size because they evaporate towards the same size of zero). Iridescence is not rare, it just requires sunglasses to view regularly.

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Re: APOD: Iridescent Clouds over Sweden (2024 Jul 07)

Post by zendae » Mon Jul 08, 2024 1:11 am

Thanks, Ann. I do love neat cloud pics, and I have a slew of'em lol...
I saw Asperatus clouds once, but mild ones. Still waiting for that glorious day.

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Re: APOD: Iridescent Clouds over Sweden (2024 Jul 07)

Post by Chris Peterson » Mon Jul 08, 2024 1:27 am

florid_snow wrote: Mon Jul 08, 2024 12:35 am If you love clouds and you love astronomy then no matter what condition the sky, you'll enjoy a look up after sunset!



But I also love nitpicking... today's APOD says that iridescent clouds are "relatively rare" but they are actually very common. If there are no clouds, you can't see iridescent clouds, of course, and if the clouds are too thick to see the sun, then you can't see iridescent clouds either. But if you have the conditions where you can both see some clouds and the sun at the same time, and then these clouds are visually near to the sun, you are guaranteed to see iridescence. It always occurs when the edge of a cloud visually approaches the edge of the sun (because the edge of the cloud always has droplets of approximately uniform size because they evaporate towards the same size of zero). Iridescence is not rare, it just requires sunglasses to view regularly.
There is some confusing terminology here. The colors we see are called "iridescence" but these are not "iridescent clouds". They are "nacreous clouds" or "polar stratospheric clouds". Iridescent clouds are seen near the Sun (or the Moon) and are common. PSCs are seen at high latitudes when the Sun is below the horizon, typically in winter, and are rare.
Chris

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Re: APOD: Iridescent Clouds over Sweden (2024 Jul 07)

Post by Lasse H » Mon Jul 08, 2024 9:57 am

Chris Peterson wrote: Mon Jul 08, 2024 1:27 am There is some confusing terminology here. The colors we see are called "iridescence" but these are not "iridescent clouds". They are "nacreous clouds" or "polar stratospheric clouds". Iridescent clouds are seen near the Sun (or the Moon) and are common. PSCs are seen at high latitudes when the Sun is below the horizon, typically in winter, and are rare.
Thank you Chris for this important discrimination between the two types of clouds, one common, one not common!