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APOD: Colorful Arcs over Buenos Aires (2015 Dec 15)
Posted: Tue Dec 15, 2015 5:12 am
by APOD Robot
Colorful Arcs over Buenos Aires
Explanation: What are those colorful arcs in the sky? Like
rainbows that are caused by rain, arcs of sunlight broken up into
component colors can also result when ice crystals floating in
Earth's atmosphere act together as a gigantic
prism. The top color arc is more typical as it is part of the
22 degree halo surrounding the Sun when
hexagonal ice crystals
refract sunlight between two of the six sides. More unusual, though, is the bottom color arc. Sometimes called a fire rainbow, this
circumhorizon arc is also created by ice, not fire nor even rain. Here, a series of horizontal, thin,
flat ice crystals in
high cirrus clouds
refract sunlight between the top and bottom faces toward the
observer. These
arcs only occur when the Sun is
higher than 58 degrees above the horizon. The featured sky occurred to the northwest in the early afternoon last month over a street Diagonal of
La Plata City,
Buenos Aires,
Argentina.
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Re: APOD: Colorful Arcs over Buenos Aires (2015 Dec 15)
Posted: Tue Dec 15, 2015 5:15 am
by Ann
That's really beautiful!
And congratulations to Sergio Montúfar, one of the stalwarts of the Recent Submissions forum, which he graces with so many fine pictures!
Ann
Re: APOD: Colorful Arcs over Buenos Aires (2015 Dec 15)
Posted: Tue Dec 15, 2015 5:53 am
by saturno2
Beautiful image, yes, yes.
Re: APOD: Colorful Arcs over Buenos Aires (2015 Dec 15)
Posted: Tue Dec 15, 2015 9:01 am
by Peter Smith
APOD Robot wrote:Here, a series of horizontal, thin, flat ice crystals in high cirrus clouds refract sunlight between the top and bottom faces toward the observer.
The refraction is not between the top and bottom faces: they are parallel so light refracted between them would not change direction. The refraction is through a 90 degree corner of the crystal formed between a vertical side face and a horizontal bottom face.
Re: APOD: Colorful Arcs over Buenos Aires (2015 Dec 15)
Posted: Tue Dec 15, 2015 12:20 pm
by neufer
Peter Smith wrote:APOD Robot wrote:
Here, a series of horizontal, thin, flat ice crystals in high cirrus clouds refract sunlight between the top and bottom faces toward the observer.
The refraction is not between the top and bottom faces: they are parallel so light refracted between them would not change direction. The refraction is through a 90 degree corner of the crystal formed between a vertical side face and a horizontal bottom face.
index of refraction of ice squared = 1.716
critical sun angle = 57.8º = sin-1(sqrt[1.716 - 1])
circumhorizon arc angle = cos-1(sqrt[1.716 - sin2(sun angle)])
Code: Select all
sun angle circumhorizon arc angle
-------------------------------------
57.8º 0.00º
58º 3.24º
59º 7.87º
60º 10.63º
61º 12.78º
62º 14.61º
65º 18.94º
67.86º 22.14º (max. bright!)
70º 24.12º
80º 30.25º
90º 31.20º
Re: APOD: Colorful Arcs over Buenos Aires (2015 Dec 15)
Posted: Tue Dec 15, 2015 12:26 pm
by Boomer12k
Awesome!!
:---(===) *
Re: APOD: Colorful Arcs over Buenos Aires (2015 Dec 15)
Posted: Tue Dec 15, 2015 1:03 pm
by starsurfer
Very nice and colourful!
![Very Happy :D](./images/smilies/icon_biggrin.gif)
Re: APOD: Colorful Arcs over Buenos Aires (2015 Dec 15)
Posted: Tue Dec 15, 2015 1:12 pm
by KryptoCleric
Why are some of the Power Lines that cross the image bent?
Was this a panorama of some type?
Re: APOD: Colorful Arcs over Buenos Aires (2015 Dec 15)
Posted: Tue Dec 15, 2015 1:48 pm
by geckzilla
KryptoCleric wrote:Why are some of the Power Lines that cross the image bent?
Was this a panorama of some type?
The whole image is bent. The street, all the wires, and the buildings are all distorted by the wide-angle lens. That one line crossing the middle is just the most apparent. One might guess that the thick drooping lines at the right side appear to droop less due to the distortion.
Re: APOD: Colorful Arcs over Buenos Aires (2015 Dec 15)
Posted: Tue Dec 15, 2015 2:14 pm
by Tirth03
I did not clearly understand the reason behind the formation of bottom arc and the 58 degree value for Sun to be above the horizon. Any reference on it will be very helpful to me!!
Re: APOD: Colorful Arcs over Buenos Aires (2015 Dec 15)
Posted: Tue Dec 15, 2015 3:42 pm
by neufer
Tirth03 wrote:
I did not clearly understand the reason behind the formation of bottom arc and the 58 degree value for Sun to be above the horizon. Any reference on it will be very helpful to me!!
Ideally, the Sun is 22.14º from zenith (i.e., 67.86º from the horizon) such that the 90º circumhorizon arc ice prism is
symmetrically positioned (
with its minimal 45.72º refraction angle) to produce a circumhorizon arc 22.14º above the horizon.
http://asterisk.apod.com/viewtopic.php? ... 38#p251538
However, if the Sun is
at zenith then the
entrance angle of the
asymmetrically positioned ice prism is 90º (i.e., parallel to the side entrance surface).
Contrariwise, if the Sun is
32.2º from zenith (i.e., 57.8º from the horizon) then the
exit angle of the
asymmetrically positioned ice prism is 90º (i.e., parallel to the bottom exit surface).
Thus the Sun is limited to being <32.2º from zenith (i.e.,
>57.8º from the horizon) for the fixed circumhorizon arc ice prism (
with its maximal 57.8º refraction angle) to work.
Re: APOD: Colorful Arcs over Buenos Aires (2015 Dec 15)
Posted: Tue Dec 15, 2015 8:24 pm
by whiskybreath
I looked out of my office at Orapa, Botswana, one day, and saw a triple cross in the sky. Photos taken with a blackberry (including the 9:00 BA Flight from Joburg (!)) but I don't know how to upload to this site without having uploaded to some other website!
A beautiful sight.
Re: APOD: Colorful Arcs over Buenos Aires (2015 Dec 15)
Posted: Tue Dec 15, 2015 9:37 pm
by neufer
whiskybreath wrote:
I looked out of my office at Orapa, Botswana, one day, and saw a triple cross in the sky. Photos taken with a blackberry (including the 9:00 BA Flight from Joburg (!)) but I don't know how to upload to this site without having uploaded to some other website!
A beautiful sight.
Below the "Save draft" "Preview" "Submit" buttons tap on "Attachments" & "Add files"
Re: APOD: Colorful Arcs over Buenos Aires (2015 Dec 15)
Posted: Tue Dec 15, 2015 10:18 pm
by bystander
neufer wrote:
Below the "Save draft" "Preview" "Submit" buttons tap on "Attachments" & "Add files"
That's only available to established members.
Re: APOD: Colorful Arcs over Buenos Aires (2015 Dec 15)
Posted: Tue Dec 15, 2015 10:20 pm
by geckzilla
bystander wrote:neufer wrote:
Below the "Save draft" "Preview" "Submit" buttons tap on "Attachments" & "Add files"
That's only available to established members.
Or to anyone who signs up for an account and then simply asks me. No need to spam for the 10 post minimum!
Re: APOD: Colorful Arcs over Buenos Aires (2015 Dec 15)
Posted: Wed Dec 16, 2015 3:01 am
by Astromontufar
Ann wrote:That's really beautiful!
And congratulations to Sergio Montúfar, one of the stalwarts of the Recent Submissions forum, which he graces with so many fine pictures!
Ann
Thank you for your kind words Ann!
Sergio
Re: APOD: Colorful Arcs over Buenos Aires (2015 Dec 15)
Posted: Wed Dec 16, 2015 4:54 am
by Astromontufar
KryptoCleric wrote:Why are some of the Power Lines that cross the image bent?
Was this a panorama of some type?
It's a panorama, sadly we have a lot of power lines all over the place, almost impossible to get rid of them.
Re: APOD: Colorful Arcs over Buenos Aires (2015 Dec 15)
Posted: Wed Dec 16, 2015 1:47 pm
by DavidLeodis
This nice image was used as the Earth Science Picture of the Day (ESPOD) on December 6 2015. For anyone like me that likes to know when a photo used an APOD was taken the information with the ESPOD states it was taken on November 21, 2015.
A quibble of mine is that the photographers name/coloured icon to the top left is distracting and would be much better placed on the bottom left or right corner. Sorry for that quibble Sergio as it is otherwise a nice photo.
Re: APOD: Colorful Arcs over Buenos Aires (2015 Dec 15)
Posted: Thu Dec 17, 2015 1:33 pm
by Whiskybreath1
Many thanks those above! Now engaging the process...