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APOD: Sun Halo over Sweden (2018 Jan 01)
Posted: Mon Jan 01, 2018 5:05 am
by APOD Robot
[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.
[/b]
Re: APOD: Sun Halo over Sweden (2018 Jan 01)
Posted: Mon Jan 01, 2018 5:35 am
by ta152h0
And a Happy New 2018 Year to this comunity and many Halos to come
Re: APOD: Sun Halo over Sweden (2018 Jan 01)
Posted: Mon Jan 01, 2018 8:16 am
by Boomer12k
WOW, that was a spectacular one!!!!
Happy New Year, Everyone!!
:---[===] *
Re: APOD: Sun Halo over Sweden (2018 Jan 01)
Posted: Mon Jan 01, 2018 12:31 pm
by heehaw
Oooohhh! I'm off to Aspen in February!
Re: APOD: Sun Halo over Sweden (2018 Jan 01)
Posted: Mon Jan 01, 2018 4:17 pm
by Chris Peterson
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).
Re: APOD: Sun Halo over Sweden (2018 Jan 01)
Posted: Mon Jan 01, 2018 5:10 pm
by BDanielMayfield
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.)
Bruce
Re: APOD: Sun Halo over Sweden (2018 Jan 01)
Posted: Mon Jan 01, 2018 5:18 pm
by Chris Peterson
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).
Re: APOD: Sun Halo over Sweden (2018 Jan 01)
Posted: Mon Jan 01, 2018 6:56 pm
by RJN
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
Re: APOD: Sun Halo over Sweden (2018 Jan 01)
Posted: Mon Jan 01, 2018 7:21 pm
by BDanielMayfield
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.
Re: APOD: Sun Halo over Sweden (2018 Jan 01)
Posted: Mon Jan 01, 2018 7:21 pm
by bystander
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.
Re: APOD: Sun Halo over Sweden (2018 Jan 01)
Posted: Mon Jan 01, 2018 7:49 pm
by BDanielMayfield
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.
That is very funny bystander.
Re: APOD: Sun Halo over Sweden (2018 Jan 01)
Posted: Tue Jan 02, 2018 12:37 am
by Chris Peterson
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.
Re: APOD: Sun Halo over Sweden (2018 Jan 01)
Posted: Mon Jun 14, 2021 2:00 am
by RJN
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