APOD: Sun Halo over Sweden (2018 Jan 01)

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APOD: Sun Halo over Sweden (2018 Jan 01)

Post by APOD Robot » Mon Jan 01, 2018 5:05 am

[img]https://apod.nasa.gov/apod/calendar/S_180101.jpg[/img] Sun Halo over Sweden

Explanation: What's happened to the Sun? Sometimes it looks like the Sun is being viewed through a giant lens. In the featured video, however, there are actually millions of tiny lenses: ice crystals. Water may freeze in the atmosphere into small, flat, six-sided, ice crystals. As these crystals flutter to the ground, much time is spent with their faces flat and parallel to the ground. An observer may find themselves in the same plane as many of the falling ice crystals near sunrise or sunset. During this alignment, each crystal can act like a miniature lens, refracting sunlight into our view and creating phenomena like parhelia, the technical term for sundogs. The featured video was taken a month ago on the side of a ski hill at the Vemdalen Ski Resort near Stockholm, Sweden. Visible in the center is the most direct image of the Sun, while two bright sundogs glow prominently from both the left and the right. Also visible is the bright 22 degree halo -- as well as the rarer and much fainter 46 degree halo -- also created by sunlight reflecting off of atmospheric ice crystals.

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Re: APOD: Sun Halo over Sweden (2018 Jan 01)

Post by ta152h0 » Mon Jan 01, 2018 5:35 am

And a Happy New 2018 Year to this comunity and many Halos to come
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Re: APOD: Sun Halo over Sweden (2018 Jan 01)

Post by Boomer12k » Mon Jan 01, 2018 8:16 am

WOW, that was a spectacular one!!!!

Happy New Year, Everyone!!
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Re: APOD: Sun Halo over Sweden (2018 Jan 01)

Post by heehaw » Mon Jan 01, 2018 12:31 pm

Oooohhh! I'm off to Aspen in February!

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Re: APOD: Sun Halo over Sweden (2018 Jan 01)

Post by Chris Peterson » Mon Jan 01, 2018 4:17 pm

APOD Robot wrote:An observer may find themselves in the same plane as many of the falling ice crystals near sunrise or sunset.
At the beginning of December in Vemdalen, the Sun never gets more than 5° above the horizon. It's basically always near sunrise or sunset (for the whole four hours the Sun is above the horizon at all).
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Re: APOD: Sun Halo over Sweden (2018 Jan 01)

Post by BDanielMayfield » Mon Jan 01, 2018 5:10 pm

Chris Peterson wrote:
APOD Robot wrote:An observer may find themselves in the same plane as many of the falling ice crystals near sunrise or sunset.
At the beginning of December in Vemdalen, the Sun never gets more than 5° above the horizon. It's basically always near sunrise or sunset (for the whole four hours the Sun is above the horizon at all).
We now live just below 44 degrees North, but in the upper Snake River Plain near Henry's Fork of the Snake River. (Great place to see bald eagle, btw) Would it be more likely to see sun dogs up in the mountains, or does elevation matter (we're just below 5000 ft.)

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Re: APOD: Sun Halo over Sweden (2018 Jan 01)

Post by Chris Peterson » Mon Jan 01, 2018 5:18 pm

BDanielMayfield wrote:
Chris Peterson wrote:
APOD Robot wrote:An observer may find themselves in the same plane as many of the falling ice crystals near sunrise or sunset.
At the beginning of December in Vemdalen, the Sun never gets more than 5° above the horizon. It's basically always near sunrise or sunset (for the whole four hours the Sun is above the horizon at all).
We now live just below 44 degrees North, but in the upper Snake River Plain near Henry's Fork of the Snake River. (Great place to see bald eagle, btw) Would it be more likely to see sun dogs up in the mountains, or does elevation matter (we're just below 5000 ft.)
Elevation itself doesn't matter. But temperature does, and if you are at a higher elevation, you may have colder air near the ground (and often times, these ice crystals aren't very high).
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Re: APOD: Sun Halo over Sweden (2018 Jan 01)

Post by RJN » Mon Jan 01, 2018 6:56 pm

At 480 kilometers distance, an emailer pointed out that Vemdalen is not really very "near" Stockholm. I therefore tweaked the NASA APOD's text to now say that the ski resort is in "central Sweden". We apologize for the oversight.

- RJN

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Re: APOD: Sun Halo over Sweden (2018 Jan 01)

Post by BDanielMayfield » Mon Jan 01, 2018 7:21 pm

Chris Peterson wrote:
BDanielMayfield wrote:
Chris Peterson wrote: At the beginning of December in Vemdalen, the Sun never gets more than 5° above the horizon. It's basically always near sunrise or sunset (for the whole four hours the Sun is above the horizon at all).
We now live just below 44 degrees North, but in the upper Snake River Plain near Henry's Fork of the Snake River. (Great place to see bald eagle, btw) Would it be more likely to see sun dogs up in the mountains, or does elevation matter (we're just below 5000 ft.)
Elevation itself doesn't matter. But temperature does, and if you are at a higher elevation, you may have colder air near the ground (and often times, these ice crystals aren't very high).
Good, as it is certainly cold enough here as it is in the single digits most nights and seldom gets above freezing now. We're learning to view the 30's as warm, like the locals.
Just as zero is not equal to infinity, everything coming from nothing is illogical.

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Re: APOD: Sun Halo over Sweden (2018 Jan 01)

Post by bystander » Mon Jan 01, 2018 7:21 pm

RJN wrote:At 480 kilometers distance, an emailer pointed out that Vemdalen is not really very "near" Stockholm.
In astronomical terms, it's very close. :mrgreen:
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Re: APOD: Sun Halo over Sweden (2018 Jan 01)

Post by BDanielMayfield » Mon Jan 01, 2018 7:49 pm

bystander wrote:
RJN wrote:At 480 kilometers distance, an emailer pointed out that Vemdalen is not really very "near" Stockholm.
In astronomical terms, it's very close. :mrgreen:
That is very funny bystander.
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Re: APOD: Sun Halo over Sweden (2018 Jan 01)

Post by Chris Peterson » Tue Jan 02, 2018 12:37 am

bystander wrote:
RJN wrote:At 480 kilometers distance, an emailer pointed out that Vemdalen is not really very "near" Stockholm.
In astronomical terms, it's very close. :mrgreen:
Indeed. A mere 5 x 10-11 light years.
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Re: APOD: Sun Halo over Sweden (2018 Jan 01)

Post by RJN » Mon Jun 14, 2021 2:00 am

Based on an email from an expert, the text of the main NASA APOD was changed to say that the 46 degree halo was also caused by refraction through ice crystals, not reflection from those crystals. I apologize for the oversight.

- RJN

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