APOD: Iridescent Clouds over Sweden (2024 Jul 07)

[APOD Robot]

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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[Guest again]

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]

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!

[Ann]

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!

Ann

[starsurfer]

I would love to have my head in those clouds!

[florid_snow]

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.

[zendae]

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.

[Chris Peterson]

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.

[Lasse H]

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!