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Aurora tonite?

 
 
Tim Conway
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      05-09-2012
Here's one to toss around awhile.

There's a solar flare today which means tonight there might be good
"northern lights" occurrences in the Northern areas.

Question: Does a polarizer on the lens help in any way; hinder; no
difference? ie. other than the usual darkening of skies, and or
reflections on water...


 
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David Dyer-Bennet
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      05-09-2012
"Tim Conway" <(E-Mail Removed)> writes:

> Here's one to toss around awhile.
>
> There's a solar flare today which means tonight there might be good
> "northern lights" occurrences in the Northern areas.
>
> Question: Does a polarizer on the lens help in any way; hinder; no
> difference? ie. other than the usual darkening of skies, and or
> reflections on water...


Now that's a fascinating question. Also, my how times have changed (the
light loss of a polarizer could not conceivably have been tolerated a
decade or two ago for a subject as faint as the aurora).

I can't think of any of the usual polarizaiton mechanisms that would
polarize parts of the aurora, and I can't think how the generating
meachanism could make it polarized to begin with, but my physics-fu is
very very amateur, so don't consider this at all conclusive.
--
David Dyer-Bennet, http://www.velocityreviews.com/forums/(E-Mail Removed); http://dd-b.net/
Snapshots: http://dd-b.net/dd-b/SnapshotAlbum/data/
Photos: http://dd-b.net/photography/gallery/
Dragaera: http://dragaera.info
 
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Me
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      05-09-2012
On 10/05/2012 5:43 a.m., Tim Conway wrote:
> Here's one to toss around awhile.
>
> There's a solar flare today which means tonight there might be good
> "northern lights" occurrences in the Northern areas.
>
> Question: Does a polarizer on the lens help in any way; hinder; no
> difference? ie. other than the usual darkening of skies, and or
> reflections on water...
>


Ideally, you should not use any filter at all, as the main green
spectral emission colour has very narrow bandwidth, and the result can
be interference patterns of converging ring patterns from internal
reflectance within the flat filter glass.

There's a large active sunspot (AR1476) coming to face our way over the
next few days, as they say "crackling with activity". If that one
really lets rip, then the results could be interesting. You can get
information and auroral oval forecasts here:
http://spaceweather.com/
 
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charles
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      05-10-2012
On Wed, 09 May 2012 20:01:51 +0200, Mxsmanic <(E-Mail Removed)>
wrote:

>Tim Conway writes:
>
>> Question: Does a polarizer on the lens help in any way; hinder; no
>> difference? ie. other than the usual darkening of skies, and or
>> reflections on water...

>
>I can't think of any reason to use a polarizer. Remember you lose a stop with
>a polarizer. And if the light that you want to record is already polarized,
>you could lose a lot more.



Not for auroras, I don't know about them, but for rainbows I've
thought a polarizer should help. The rainbow light is polarized, the
polarizer will blank it out, so 90 degrees from there it should reduce
the background light and seemingly enhance the rainbow.

I haven't had the camera, polarizer and rainbow together all at the
same time to try it.

 
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PeterN
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      05-10-2012
On 5/9/2012 5:11 PM, Me wrote:
> On 10/05/2012 5:43 a.m., Tim Conway wrote:
>> Here's one to toss around awhile.
>>
>> There's a solar flare today which means tonight there might be good
>> "northern lights" occurrences in the Northern areas.
>>
>> Question: Does a polarizer on the lens help in any way; hinder; no
>> difference? ie. other than the usual darkening of skies, and or
>> reflections on water...
>>

>
> Ideally, you should not use any filter at all, as the main green
> spectral emission colour has very narrow bandwidth, and the result can
> be interference patterns of converging ring patterns from internal
> reflectance within the flat filter glass.
>
> There's a large active sunspot (AR1476) coming to face our way over the
> next few days, as they say "crackling with activity". If that one really
> lets rip, then the results could be interesting. You can get information
> and auroral oval forecasts here:
> http://spaceweather.com/



Fascinating site. thanks for posting.

--
Peter
 
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Me
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      05-11-2012
On 11/05/2012 10:54 a.m., PeterN wrote:
> On 5/9/2012 5:11 PM, Me wrote:
>> On 10/05/2012 5:43 a.m., Tim Conway wrote:
>>> Here's one to toss around awhile.
>>>
>>> There's a solar flare today which means tonight there might be good
>>> "northern lights" occurrences in the Northern areas.
>>>
>>> Question: Does a polarizer on the lens help in any way; hinder; no
>>> difference? ie. other than the usual darkening of skies, and or
>>> reflections on water...
>>>

>>
>> Ideally, you should not use any filter at all, as the main green
>> spectral emission colour has very narrow bandwidth, and the result can
>> be interference patterns of converging ring patterns from internal
>> reflectance within the flat filter glass.
>>
>> There's a large active sunspot (AR1476) coming to face our way over the
>> next few days, as they say "crackling with activity". If that one really
>> lets rip, then the results could be interesting. You can get information
>> and auroral oval forecasts here:
>> http://spaceweather.com/

>
>
> Fascinating site. thanks for posting.
>

Yes.
There's been a bit of media coverage of solar events as we're
approaching "solar maximum", probably due to better observation and
fantastic images/video from SDO in particular, but probably also genuine
concern about communication satellites etc, and popular doomsday theory
of all kinds.
But this solar maximum looks like being a bit of a fizzer:
http://www.swpc.noaa.gov/SolarCycle/index.html
Tracking very close to (200 "consensus" prediction.
(I did read some prediction a few years ago claiming that as we'd come
out of a very low solar minimum, we were in for a massive solar maximum
- but so far the consensus view seems to be right)
This solar maximum probably isn't going to be a great period for
auroras, but OTOH digital photography means we'll probably see some
great photos.
The M5 flare yesterday got some media attention, but there was no CME
headed our way, and the impact seems to have been only an "R2" radio
blackout:
http://www.swpc.noaa.gov/NOAAscales/...RadioBlackouts
which from the table, happens 350 times / 300 days over a typical solar
cycle. Hardly an unusual event (beautiful SDO video of the flare though).
This news:
http://www.theregister.co.uk/2012/05...ed_by_the_sun/
appeared in only a few newspapers worldwide. The implications might
have been seen to be a bit hot to handle - or perhaps science reporters
don't bother to report news unless hollywood covers the topic first.


 
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Gordon Freeman
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      05-11-2012
charles <(E-Mail Removed)> wrote:

> Not for auroras, I don't know about them, but for rainbows I've
> thought a polarizer should help. The rainbow light is polarized, the
> polarizer will blank it out, so 90 degrees from there it should reduce
> the background light and seemingly enhance the rainbow.
>
> I haven't had the camera, polarizer and rainbow together all at the
> same time to try it.


I've successfully used that approach to enhance reflections but not tried
it for rainbows as it hadn't occurred to me that they might be polarised.

 
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Chris Malcolm
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      05-13-2012
Gordon Freeman <(E-Mail Removed)> wrote:
> charles <(E-Mail Removed)> wrote:


>> Not for auroras, I don't know about them, but for rainbows I've
>> thought a polarizer should help. The rainbow light is polarized, the
>> polarizer will blank it out, so 90 degrees from there it should reduce
>> the background light and seemingly enhance the rainbow.
>>
>> I haven't had the camera, polarizer and rainbow together all at the
>> same time to try it.


> I've successfully used that approach to enhance reflections but not tried
> it for rainbows as it hadn't occurred to me that they might be polarised.


If the angle of the polarisation depends on the effective angle of
reflection then a polarising filter will emphasize one part and
de-emphasize others. The same problem which makes blue sky
intensification with a polariser work well with long focal length
lenses and be worse than useless with wide angle lenses.

--
Chris Malcolm

 
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