2. a collective name for everything having to do with
light and color in the atmosphere, which includes
subjects on the ground.
It deals with how the unique optical
properties of the earth’s
atmosphere cause a wide range of
spectacular optical phenomena.
Why the sky is blue?
What causes the color of the
sunset and sunrise?
What is halo?
And many more optical wonders..
Or illusions?
3. All electromagnetic radiation is light, but we can only see
a small portion of this radiation—the portion we call
visible light.
Possible fates of light as it enters atmosphere
(absorbed, reflected, scattered, transmitted)
Our eyes are sensitive to light which lies in a very small
region of the electromagnetic spectrum labeled "visible
light".
This "visible light" corresponds to a wavelength range of
400-700 nanometers (nm) and a color range of violet
through red
4. Reflection – occurs when sunlight
bounces off a surface at same angle
Scattering – occurs when sunlight is
deflected in all directions
Refraction- bending of light due to
density changes.
Diffraction – bending of light around
objects
Transmission- the process by which
light energy is transmitted
Absorption- the process by which
light is taken by the substance.
5. The organ of adaptation is our eyes and, more
specifically, specialized receptors located on a layer
of cells called the retina at the back of the eye.
These special receptors consist of two
types of cells:
1.Rods respond to all the wavelengths of
light, and can only differentiate between
light and dark.
2. Cones respond to specific
wavelengths within the visible spectrum
and our brain interprets the signals from
cones activated by longer wavelengths
as red and those by shorter wavelengths
as blue with those in between as green.
6. Perception of color:
◦ Each color
corresponds to a
particular
wavelength.
◦ White: all
wavelengths are
present with equal
intensity;
◦ Black: no light is
emitted and/or
reflected from the
object.
7. ◦ The sun appears white (in the
atmosphere).
◦ Colder stars look redder
◦ Hotter stars look bluer
◦ Our Sun produces more
yellow light than any other
color because its surface
temperature is 5,500°C.
◦ If the Sun's surface were
cooler—say 3,000°C—it
would look reddish, like the
star Betelgeuse.
◦ If the Sun were hotter—say,
12,000°C—it would look blue,
like the star Rigel.
8. Color is a function of the human visual system, and is
not an intrinsic property.
Objects don't "have" color, they give off light that
"appears" to be a color.
Spectral power distributions exist in the physical world,
but color exists only in the mind of the beholder.
The color of the object is based upon the wavelength of
visible light that is reflected by the object.
The red apple looks red because the all short wave
lengths are absorbed except which is reflected back.
9. The scattering of light in the atmosphere depends on the size of
the scattering particles, R, and on the wavelength, l, of the
scattered light.
Geometric scattering: R>> l
◦ Rain drops (R~10-100 mm)
◦ All wavelengths equally scattered
◦ Optical effects: white clouds
Mie scattering: R~ l
◦ Aerosols (R~0.01-1 mm)
◦ Red scattered better than blue
◦ Blue moon, blue sun
Rayleigh scattering: R<< l
◦ Air molecules (R~0.0001-0.001 mm)
◦ Blues scattered better than red
◦ Blue sky, blue mountains, red sunsets
l
l
l
R
R
R
10.
11. Blue Sky
◦ Involves gases, or other scattering
agents that are smaller than the energy
wavelengths
◦ Scatter energy forward and backward
◦ Partial to shorter wavelength energy,
such as those which inhabit the shorter
portion of the visible spectrum
◦ A blue sky results
Hazy Sky
◦ When larger particles such as dust
and pollutants are present in the
atmosphere, particularly when water
vapor condenses on them to form tiny
water droplets), they are large enough
to scatter all wavelengths of light
◦ The sky then takes on a milky white
appearance
12. White Clouds
◦ Water vapor (clouds) scatter all
wavelengths equally. The result
is white.
◦ When clouds are thick (like
thunderclouds) they absorb
much of the light. Water drops
also tend to absorb light. The
result is a darker cloud.
Red/Orange Clouds
◦ At sunset or sunrise the colour
of sunlight can be yellow to
deep red due to the scattering
of the blue component of
sunlight as the light travels a
longer path through the
atmosphere.
13. Grey clouds
As a cloud grows thicker, more
sunlight is reflected from it and
less light can penetrate through it.
Since little sunlight reaches the
underside of the cloud, less light
is scattered, and the cloud base
appears grey. Moreover, if the
water droplets near the cloud
base grow larger, they become
less effective scatterers and more
effective absorbers.
Blue clouds
Common to noctilucent clouds
particularly in the Antarctic region.
Caused by increased methane
production in the higher
atmosphere.
Sign of climate change
14. This works particularly well after major Volcanic Eruptions, when
sunlight is scattered at sulfuric acid droplets in the stratosphere, as
after the eruption of Mt. Pinatubo.
15. The sun looks yellow, since a part
of the blue light has been scattered
away.
Near sunrise and sunset the path
through the atmosphere (air mass
factor) is very long, the major part
of the blue light has been scattered
away, the orange and red part of
the spectrum remains.
Due to Mie-Scattering at dust
particles in the atmosphere also the
surrounding of the sun is red or
orange.
16. Earth Shadows (dark segments) are names for
the shadow that the Earth itself casts on its
atmosphere.
17. Known as Venus girdle or anti-twilight arch, is a
pink to brownish border separating the dark
shadow band of the earth from the sky above it.
18. Shadow casts by cloud appearing darker.
Cloud shadow occurring at sunset is formed when
light is cast from a low level cloud onto a higher
level cloud.
19. The triangular shadow cast by the mountain at the
top of the summit regardless of the mountain’s
shapes.
The finite size of the
sun causes the umbral
(fully shaded) parts of
the shadow to
converge and
eventually taper away.
Higher mountains are
best to cast long
triangular shadow.
20. Sun rays, also called crepuscular rays,
streaming through gaps in clouds are parallel
columns of sunlit air separated by darker cloud
shadowed regions.
21. Anticrepuscular rays or antisolar rays are similar
to crepuscular rays, but seen opposite the sun in
the sky.
22. The color of the moon is also caused by the scattering. The
orange color of the moon is because other colors are
scattered except for the orange and red that remain. The
whitish color is due to dust particles in the atmosphere.
23. Green flashes and green rays are optical
phenomena that sometimes occur right after
sunset or right before sunrise.
When the conditions are
right, a green spot is
visible above the upper
rim of the disk of the
sun.
The green appearance
usually lasts for no more
than a second or two.
24. Even more elusive than the “green flash” are its blue and violet variants.
Blue and violet light is subject to larger refraction, but also to more intense
scattering.
25. Due to the refraction of
light the objects on the
sky appear higher than
they actually are.
◦ Star location and
scintillations;
◦ Timing of the sunset and
the sunrise;
◦ The sun on the horizon
looks flattened;
◦ Twilight duration.
26. Scintillation-The apparent
twinkling of star due to
refraction.
The changing density will
change the amount of
refraction with cold,
dense pockets refracting
more and warm pockets
less
As the air in the
atmosphere flows and
moves these pockets, the
“apparent” position of
the star will change with
the star appearing to
flicker or “twinkle”
27. The bending of sunlight by the atmosphere causes
the sun to rise about two minutes earlier, and set
about two minutes later, than it would otherwise.
28. Light in the atmosphere travels along a curved path, due to
continuous refraction. When the sun is at the horizon,
light from the lower edge is significantly stronger refracted
than from the upper edge – and appears to be higher –
resulting in a flattened image of the sun.
Les Cowley
29. This is even more pronounced when observing a
moonset from the International Space Station (ISS),
since the path through the atmosphere is twice as long.
30. Atmospheric layers with different air density can cause
bizarre distortions of the sun’s image .
31. An unusually warm layer of air over the ocean can
produce an inferior mirage causing double sun.
32. An optical illusion described by
Italian psychologist Mario Ponzo
known as “ Ponzo illusion”,
suggested that the human mind
judges an object's size based
on its background.
33. Supermoon is the coincidence
of a full moon or a new
moon with the closest approach
the moon makes to the Earth on
its elliptical orbit, resulting in the
largest apparent size of the lunar
disk as seen from Earth.
It is also known as Perigee Full
Moon.
The technical name is
the perigee-syzygy of the
Earth–Moon–Sun system.
March 19, 2011, May 6, 2012, June 23, 2013
August 10, 2014, September 28, 2015
November 14, 2016, January 2, 2018
The full moon on November 14, 2016 was the closest
supermoon of the year (356,509 kilometers or 221,524
miles). What’s more, this November 14, 2016 full moon will
showcase the moon at its closest point to Earth thus far in
the 21st century (2001 to 2100), and the moon won’t come
this close again until the full moon of November 25, 2034.
34. Twilight is the name given to the time after sunset
(and immediately before sunrise) when the sky
remains illuminated and allows outdoor activities
to continue without artificial lighting.
Civil twilight lasts from sunset
until the sun is 6° below the
horizon.
Astronomical twilight lasts until
the sky is completely dark and th
astronomical observation of the
faintest stars is possible.
35. The length of twilight depends on season and
latitude.
During the summer in middle latitudes, twilight
adds about 30 minutes of light to each
morning and evening for outdoor activities.
The duration of twilight increases with
increasing latitude, especially in summer.
At high latitudes during the summer, morning
and evening twilight may converge, producing
a white night — a nightlong twilight.
In general, without the atmosphere, there
would be no refraction or scattering, and the
sun would rise later and set earlier than it now
does.
Instead of twilight, darkness would arrive
immediately when the sun disappears below
the horizon.
36. Mirage – an image that appears displaced from its
true position
Caused by light moving through different air
densities
Inferior mirage – images that appear lower and
inverted from original
Superior mirage – images that appear higher
than original
37. Warm surface, decreasing temperatures aloft
• The proper conditions for an inferior mirage are commonly found over
a hot road surface during summer, or over an unfrozen lake on a very
cold day.
38. Cold surface, warmer temperature aloft
• The proper conditions for a superior mirage are commonly
found over water and over snow-covered surfaces.
39. is an unusual and complex form of superior
mirage that is seen in a narrow band right above
the horizon.
Fata Morgana mirages significantly
distort the object or objects on
which they are based, often such
that the object is completely
unrecognizable.
A Fata Morgana can be seen on
land or at sea, in polar regions or in
deserts. This kind of mirage can
involve almost any kind of distant
object, including boats, islands and
the coastline.
40. an optical phenomenon produced by ice crystals
creating colored or white arcs and spots in the
sky.
The preferred angular distance
for halos are 22 and 46 degrees
from the ice crystals which
create them
41. Dispersion – breaking up of light into different
wavelengths (prism)
42. Tangent arc - an arc of light tangent to a halo. It
forms by refraction of light through ice crystals
Refraction of sunlight through the
ice crystals produces the bright arc
of light.
When the sun is on the horizon, the
arc that forms at the top of the halo
is called an upper tangent arc.
When the sun is above the horizon,
a lower tangent arc may form on
the lower part of the halo beneath
the sun.
43. atmospheric phenomenon that consists of a pair of
bright spots on either side on the Sun, often co-
occurring with a luminous ring known as a 22°
halo. Created by hexagonal ice
crystals oriented horizontally
Ice crystals act like a prism
Sundogs are commonly
seen when cirrostratus
clouds are in the sky.
44. Moondog (paraselenae)- A relatively rare bright circular
spot on a lunar halo caused by the refraction of
moonlight by hexagonal-plate-shaped ice crystals in
cirrus and cirrostratus clouds.
They are exactly analogous
to sun dogs, but are rarer
because to be produced the
moon must be bright, about
quarter moon or more.
Moondogs show little color to the
unaided eye because their light is
not bright enough to activate the
cone cells of the human eye.
45. A parhelic circle is a white band circling the sky
and always at the same height above the horizon
as the sun
If complete, it stretches all around
the sky, but more commonly it only
appears in sections.
Even fractions of parhelic
circles are less common than sun
dogs and 22° halos
46. A sun pillar is a vertical shaft of light extending upward
or downward from the sun.
Caused by reflection of light
off ice crystals
Typically seen during
sunrise or sunset, sun
pillars form when sunlight
reflects off the surfaces of
falling ice crystals
associated with thin, high-
level clouds (like
cirrostratus clouds).
47. Sun pillars are created by reflection on tilted ice crystals
48. Rainbow-phenomenon that is caused by
reflection, refraction and dispersion of light in
water droplets resulting in a spectrum of light
appearing in the sky.
49. Cloud drop act as prism, dispersing light
Rainbows are caused by (double) refraction at the surface
and reflection.
On the backside of spherical raindrops. This can happen
under different angles, but there is a maximum angle of 42°.
Violet light emerges from the “front” side of the raindrop at a
40° angle and red at 42°
50.
51. a phenomenon in which two rainbows appear
They are about 127° (violet) to 130° (red)
wide.
Since this is more than 90°, they are seen
on the same side of the sky as the primary
rainbow, about 10° above it at apparent
angles of 50–53°.
As a result of the "inside" of the secondary
bow being "up" to the observer, the colours
appear reversed compared to the primary
bow.
The secondary rainbow is fainter than the
primary because more light escapes from two
reflections compared to one and because the
rainbow itself is spread over a greater area of
the sky.
52. A second rainbow appears (at an angle of ~ 51°), when
the light is reflected twice inside the raindrop. Note the
reversed order of the colors and Alexander’s dark
band in between.
53. Alexander's band or Alexander's dark band is
an optical phenomenon associated with
rainbows which was named after Alexander of
Aphrodisias who first described it in 200 AD.
It occurs due to the deviation
angles of the primary and
secondary rainbows.
Both bows exist due to an
optical effect called the angle of
minimum deviation.
The refractive index of water
prevents light from being
deviated at smaller angles.
54. Twinned rainbow- appears as two rainbow arcs that split
from a single base.
The colours in the second bow, rather than reversing as in
a double rainbow, appear in the same order as the primary
rainbow. Twinned rainbows are (most
likely) caused by non-spherical,
large raindrops
Due to air resistance, raindrops
flatten as they fall, and flattening is
more prominent in larger water
drops.
When two rain showers with
different-sized raindrops combine,
they each produce slightly different
rainbows which may combine and
form a twinned rainbow
55. A complete rainbow, which is visible in the higher
altitude and a clear sky.
In theory every rainbow is a
circle, but from the ground only
its upper half can be seen.
Since the rainbow's centre is
diametrically opposed to the
sun's position in the sky, more
of the circle comes into view as
the sun approaches the horizon,
meaning that the largest section
of the circle normally seen is
about 50% during sunset or
sunrise.
56. A supernumerary rainbow—also known as a stacker
rainbow—is an infrequent phenomenon, consisting of
several faint rainbows on the inner side of the primary
rainbow, and very rarely also outside the secondary
rainbow.
They are caused by
interference – they
provided a first hint
that light can act
like a wave.
57. Reflected bows are made by rays that are reflected
by the water surface after they have passed through
raindrops.
The lower bow, although it is called a
"reflected bow", is not a reflection of
the upper one.
Rainbows are not real objects and
therefore cannot produce reflections.
The reflection inverts the rainbow and
the bow centre is then above the
horizon at the anthelic point. The
reflection bow and ordinary bow meet
in a cusp at the horizon.
58. A reflection rainbow may be produced where
sunlight reflects off a body of water before reaching
the raindrops, if the water body is large, quiet over its
entire surface, and close to the rain curtain.
The reflection rainbow appears
above the horizon.
It intersects the normal rainbow at
the horizon, and its arc reaches
higher in the sky, with its centre as
high above the horizon as the
normal rainbow's centre is below it.
Due to the combination of
requirements, a reflection rainbow is
rarely visible.
59. Red rainbow or monochrome rainbow- a rare type of
rainbow where it happen during sunrise or sunset with
occasional shower, causing the shorter wavelengths like
blue and green scattered of which the longer
wavelength, red , remain.
60. Formation of rainbows of higher orders even up to
sixth order.
The order of a rainbow is determined
by the number of light reflections inside
the water droplets that create it:
One reflection results in the first-order
or primary rainbow; two reflections
create the second- order or secondary
rainbow.
An additional challenge in observing
the third-order (or tertiary) and fourth-
order (quaternary) rainbows is their
location in the direction of the sun.
Brightness decreases as order
increases.
61. is a rainbow produced by light reflected off the
surface of the moon (as opposed to direct
sunlight) refracting off of moisture laden clouds in
the atmosphere.
Moonbows are relatively faint, due to
the smaller amount of light reflected
from the surface of the moon.
They are always in the opposite part
of the sky from the moon
62. A bow like the rainbow, formed in cloud droplets.
As cloud droplets are much smaller
than raindrops, the spectral colors of
the white light have a much larger
range of exit angles from a droplet,
and as a result, the colors overlap so a
white bow is produced.
63. Fogbows form in the same way as rainbows, but
they are formed by much smaller cloud and fog
droplets that diffract light extensively.
They are almost white
with faint reds on the
outside and blues inside.
The colours are dim
because the bow in each
colour is very broad and
the colours overlap.
64. Brocken bow or mountain spectre, is the
apparently enormous and magnified shadow of an
observer, cast upon the upper surfaces of clouds
opposite the sun. From above a cloud you may see your own
shadow (at the anti-solar point) as
“Brocken Spectre“, surrounded by a glory.
The phenomenon is named after Brocken,
the highest elevation in the Harz mountain
range, where it can be frequently observed
65. An arc formed directly overhead, the zenith, about 45o
above the sun as platelike ice crystals fall with their
flat surfaces parallel to the ground.
This is caused by refraction of
light into ice crystals (cirrus clouds).
Circumzenithal arc can only form
when the sun is lower than 32°
above the horizon.
When the sun is higher than this
angle, the refracted light cannot be
seen by the observer.
While rainbow is formed when it
rain, circumzenithal arc is not.
66. A glory is an optical phenomenon that resembles an
iconic saint's halo about the shadow of the observer's
head
Each observer will see a
glory around its own head
– and no glories around
those of others.
Sun must be to your
back, cloud in front of you
The formation of glories
is still not entirely
understood.
67. Corona – Bright ring of light around the moon or
sun
A corona is caused through
diffraction by small particles –
usually by cloud droplets
Blue appears on inside of ring,
red on outside.
Need a cloud that has droplets
of similar size
New clouds are the best
corona producers
68. Heiligenschein – (German for halo) a faint white ring
surrounding the shadow of an observer’s head on a
dew-covered lawn.
The Heiligenschein forms when
sunlight, which falls on nearly spherical
dew drops, is focused and reflected back
toward the sun along nearly the same
path that it took originally. (Light reflected
in this manner is said to be
retroreflected.)
The light, however, does not travel
along the exact path; it actually spreads
out just enough to be seen as bright
white light around the shadow of your
head on a dew-covered lawn.
69. Cloud iridescence is the occurrence of colors in
a cloud similar to those seen in oil films on
puddles. Associated with thin clouds.
It is a fairly uncommon
phenomenon, most often observed
in altocumulus, cirrocumulus,
lenticular clouds and cirrus clouds.
The colors are usually pastel, but
can be very vivid.
Iridescence is generally
produced near the sun, with the
sun's glare masking it, so it is more
easily seen by hiding the sun
behind a tree or building.
70. An aurora is a natural light display in the sky,
predominantly seen in the high latitude (Arctic and
Antarctica) regions.
Aurora borealis- northern lights
Aurora australis- southern lights
The aurora forms when charged
particles emitted from the sun during
a solar flare penetrate the earth's
magnetic shield and collide with
atoms and molecules in our
atmosphere.
These collisions result in
countless little bursts of light, called
photons, which make up the
aurora.
