Atmospheric Effects are Looking Up - Orwell Astronomical · Atmospheric Effects caused by Ice...
Transcript of Atmospheric Effects are Looking Up - Orwell Astronomical · Atmospheric Effects caused by Ice...
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Atmospheric Effects are Looking Up
OASI Workshop 21st May 2018
by Olaf Kirchner
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Ever seen one of these ?
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OK, so how about one of these?
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Atmospheric Effects
- caused by sun- or moonlight interacting with liquid water or ice in the air
- surprisingly common
- always beautiful and one or several phenomena may be seen at the same time
- can be in-your-face obvious or very subtle, and ... - ... span the entire sky - a challenge to photograph
- very complicated theoretical explanations
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Effects caused by Liquid Water Droplets
- rainbows
- glories, Heiligenschein and the Spectre of the Brocken
- aureoles / coronae
- nacreous / iridescent / Mother-of-Pearl clouds
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Rainbow
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Rainbow
Ray paths for secondary rainbow
Ray paths through a spherical water drop
Ray paths for primary rainbow
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Secondary Rainbow
Alexander’s Band
Supernumerary rainbow
Secondary rainbow
Primary rainbow
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Rainbow
Rainbow in spray, Geneva Jet d’Eau
Gap in cloud behind observer = partial rainbow
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Supernumerary Rainbow
Interference colours from different lengths of light path
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Rainbow
Circular rainbow seen from an aircraft
Rainbows don’t reflect ...
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Glory
Colourful diffraction rings centred on the antisolar point, caused by reflection from spherical droplets
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Glory
... i.e. centred on where the shadow of your head would be!
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Brockengespenst = Spectre of the Brocken
Taken against fog from Golden Gate Bridge
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Brocken (1142 m)
Highest point in the Harz mountains
.
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Heiligenschein = Halo
Antisolar point in hydrothermal steam ... scary stuff
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Heiligenschein
... i.e. a glory centred on your head
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“Dry Heiligenschein”
Light area around antisolar point (around aircraft shadow)
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“Dry Heiligenschein”
... caused by leaves shading leaves
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Aureole (Corona)
More diffraction going on
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Aureole (Corona)
Beautiful colours if you’re lucky
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Nacreous / Mother-of-Pearl / Iridescent Cloud
Diffraction effect - colours depend on
angular distance from the sun and droplet
size !
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Nacreous / Mother-of-Pearl / Iridescent Cloud
One of my favourite lamp post pictures
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Atmospheric Effects caused by Ice Crystals
- historical observations
- what shapes are the crystals and why are their effects so complex?
- reflections from crystals (subsuns, sun pillars)
- halos and associated zoo (sundogs, circumscribed halos, tangent arcs, circumzenithal arcs, parhelic circles etc. etc.)
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Historical Observations of Atmospheric Effects
Seven Suns by Hevel (Hevelius), Gdansk / Danzig 1662
Computer Simulation
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Historical Observations of Atmospheric Effects
Lovitz, St. Petersburg 1790
Computer Simulation
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Common Atmospheric Effects
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Ice Crystals
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Ice Crystals
Perfect hexagonal plates and pencils / needles (rare!)
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Ice Crystals: Plates and Pencils / Needles
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Sun Pillar
Reflection off horizontal surfaces
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Subsun
Reflection off horizontal surfaces of ice crystals below
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Subsun
No layer of ice crystals, sun reflects from ocean
Layer of ice crystals below = subsun
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22o Halo
Well formed randomly oriented hexagonal ice crystals
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22o Halo
... a professional shot
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Circumscribed Halo
Frequently see just top and bottom edges of 22o halo
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Sun Dogs (Parhelia)
... caused by well formed, falling pencil ice crystals
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Sun Dogs (Parhelia)
Sunset from above
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Circumzenithal Arc
Don’t forget to look right up!
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Circumzenithal Arc
Ray path and simulation
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Multiple Atmospheric Effects
Parhelion (sun dog) and Parhelic Circle
Sun Pillar and Subsun
22o Halo
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Multiple Atmospheric Effects – 5 minutes later
Parhelion (sun dog)
Subsun
22o Halo
Sub-parhelion
Parhelion (sun dog)
Sub-parhelion
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Parhelic Circle
22o Halo
Parhelic Circle and 120o Brightening
Parhelic Circle and 240o Brightening
Parhelic Circle
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Multiple Atmospheric Effects
... once on a lifetime sight
46o Halo
Parhelion
Parry arc and circumscribed halo
Circumzenithal arc
22o Halo
Parhelic circle
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Multiple Atmospheric Effects
46o Halo
Parhelion
Parry arc and circumscribed halo
Circumzenithal arc
22o Halo
Parhelic circle
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If you want to know more ...
“Rainbows, Halos, and Glories” by Robert Greenler (1980) = The Book
“The nature of Light and Colour in the Open Air” (1954) by Marcel Minnaert = The Other Book
Downloadable simulations program (including for extraterrestrial displays) from atoptics.co.uk
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atoptics.co.uk