www.alisondemarco.com
alison-demarco1@virginmedia.com
+44 7716669566
COLOUR IN NATURE
Many materials, both natural and man-made, can be irradiated to produce colour centres. For
example, if you left a century-old glass bottle in the desert, exposed to the ultraviolet
radiation present in strong sunlight, for ten years, it would acquire an attractive purple colour.
If you were then to heat the bottle in an oven, the colour would disappear. If the bottle was
exposed to an intense source of energetic radiation, as in the cobalt-60 gamma ray cell, within
a few minutes an even deeper purple colour would appear.
The colour of this ‘desert amethyst glass’ derives from a colour centre, as do the colours of
the natural gemstones amethyst, smoky quartz and blue and orange topaz. Other natural and
man-made materials can be irradiated to produce colour centres, including irradiated blue,
yellow and green diamond. Some of these are perfectly stable and lose their colour only when
The Elite Human Nature System
 October 2001.
1
www.alisondemarco.com
alison-demarco1@virginmedia.com
+44 7716669566
heated. Other colour centres are unstable and fade when exposed to light, while others can
fade even in the dark.
A century ago, glass was decolourised with manganese additions to remove the green colour
caused by iron impurities. Natural yellow-to-orange-to-brown precious topaz contains a
colour centre stable to light. Colourless topaz can be irradiated to a similar colour, but is
usually unstable and fades in a few days in light. Blue topaz also contains a colour centre,
which can be either natural or man-produced. However, the exact nature of colour centres is
unknown. The irradiation of colourless diamonds can produce stable yellow, blue, brown and
green colours.
Diffraction is the term used to describe the spreading of light at the edges of an object. The
Italian professor of mathematics, F. Grimaldi, in his posthumous book published in 1665,
described in detail how diffraction was incontrovertible proof for the wave nature of light.
Grimaldi studied the shadows of small objects, using a small opening in a window shutter. He
observed that these shadows were larger than could be accounted for by geometric
considerations and noted the colour fringes, not only outside but even inside the shadow
under certain conditions. He coined the word ‘diffraction’ for the effects he noted, but was
unable to explain. Subsequent investigations followed, but adequate explanations and
descriptions were only found by three contemporaries, Thomas Young (1773-1829), Joseph
von Fraunhofer (1778-1826) and, particularly, Augustin Fresnel (1788-1827).
Consider sunlight passing through an aperture and falling onto a screen. As the opening is
made smaller, the patch of light on the screen becomes smaller and at the same time its edges
appear to become sharper. Beyond a certain point, however, the edges become indistinct and
begin to show coloured fringes. This involves the spreading of a wave into the geometrical
shade region of an object. A single edge in monochromatic light produces a sequence of light
and dark bands, while in white light a sequence of colours is produced. When light beams
diffracted from opposite sides of small particles interfere, the result is a sequence of coloured
rings, called the ‘corona’, usually seen around a bright light source,(not to be confused with
the solar corona seen during an eclipse). This can frequently be seen surrounding the sun
(using dark sunglasses), derived from cloud particles.
The Elite Human Nature System
 October 2001.
2
www.alisondemarco.com
alison-demarco1@virginmedia.com
+44 7716669566
The most outstanding diffraction rating of all is the gemstone opal, which shows flashes of
various colours on a white or black background. Electron-microscope pictures taken of an
opal reveal that it has a regular three-dimensional array of equal-sized spheres. The
composition of the spheres is amorphous silica, containing a small amount of water. The
spheres are cemented together with more amorphous silica, containing a different amount of
water, so that a small refractive index difference exists between the spheres and the cement.
Liquid crystals are organic compounds with a structure intermediate between that of a crystal
and that of a liquid. These have twisted structures, which can interact with light in a manner
similar to diffraction, to produce colour.
Shadows
Shadows can be both volumes of space and areas that are blocked from light. A shadow from
a point source of light e.g. star, has sharp edges and is called an umbra (= shadow receiving
no light). If the light source is large then the shadow will consist of both an umbra and
penumbra (= shadow receiving some light). If you stand in the umbra it is impossible to see
the light source, whereas in a penumbra it is possible to partially see the light source. A
The Elite Human Nature System
 October 2001.
3
www.alisondemarco.com
alison-demarco1@virginmedia.com
+44 7716669566
shadow can have colour, it depends on both the colour of the light and the colour of the
surface onto which the shadow is projected. A shadow can never be totally dark and it is
possible for opaque items to cast shadows.
Specter of the broken are 3-d shadows. They usually occur when an object is between a
light source and fog.
Contrail shadows are shadows of condensation trails of aeroplanes.
AIR
The Elite Human Nature System
 October 2001.
4
www.alisondemarco.com
alison-demarco1@virginmedia.com
+44 7716669566
RAYS
Rays or sunbeams as they are sometimes called are streams of light extending radially from
the sun. Rays can be both dark and light depending on the background colour. Rays always
point to the sun, even when it is below the horizon.
SUNLIGHT
The sunlight that reaches the surface of the earth is only a fraction of the light that hits the
earth’s atmosphere. The remainder of the light is absorbed (converted to heat) or scattered (=
redirected) by dust particles and the air itself. Airlight is the term used to describe sunlight
scattered by air molecules between the viewer and the object. Airlight is seen as a blue veil.
Haze is not airlight as haze can be brown, white or gray, airlight is always blue. Haze is due
to fine particles that are small enough to introduce a slight coloration. Airglow is the feeble
light emitted from the upper atmosphere and is the uniform glow in the night sky.
The Elite Human Nature System
 October 2001.
5
www.alisondemarco.com
alison-demarco1@virginmedia.com
+44 7716669566
COLOUR CHANGES OF THE SUN
The sun changes colour depending on how high it is in the sky. The higher the sun is in the
sky the more white it appears, as there is only a small amount of light removed. However, as
the sun approaches the horizon the colour changes - yellow, orange to deep red. This is due to
high scattering of the sunlight by air molecules, dust and smoke particles. The bright ring of
whitish light that circles the sun is called the aureole, which can be easily seen if the sun
shines through high clouds, yet not through low clouds. The faint bluish circle which is
surrounded by a ruddy ring that sometimes circles the sun is called the Bishop’s ring.
TWILIGHT
The time period when the sun is below the horizon but continues to light up the sky is known
as twilight. Dusk is twilight following sunset, dawn is twilight before sunrise. The twilight
The Elite Human Nature System
 October 2001.
6
www.alisondemarco.com
alison-demarco1@virginmedia.com
+44 7716669566
arch is the arch of yellowish light that appears on the western horizon at sunset. It is due to
the scattering of sunlight due to the atmosphere. The anti-twilight arch is the arch of pinkish
light that appears on the eastern horizon. The dark blue band that is beneath it is the earth
shadow.
The Elite Human Nature System
 October 2001.
7
www.alisondemarco.com
alison-demarco1@virginmedia.com
+44 7716669566
ALPENGLOW AND PURPLE LIGHT
When the twilight arch or sunlight is reflected off the mountains, the mountains take on a
purple glow. This is alpenglow. The purple glow that appears sometimes in the sky after the
sun is below the horizon is called purple light. It is due to the scattering of light from
stratospheric dust.
HORIZONS AND RELATED PHENOMENA
There are three types of horizon: the astronomical horizon
(= imaginary plane which passes from the observers eye, perpendicular to the zenith),
The geometric horizon (= plane separating land from sea)
The Elite Human Nature System
 October 2001.
8
www.alisondemarco.com
alison-demarco1@virginmedia.com
+44 7716669566
The sea-level horizon
(= due to diffraction of the geometric horizon upwardly displaced by the astronomical
horizon ). It is the sea-level horizon that one usually means when one speaks of the ‘horizon’.
Sometimes it is not possible to make out where the horizon is. This can be because the sky
and the sea appear the same colour (when the sea is flat and calm), or when the sky is
overcast.
The flattening of the sun and moon at the horizon is due to atmospheric refraction (=
change in the direction of light as it passes through one medium to another with different
index of refraction.). However sometimes the sun and moon appears distorted or fragmented.
This is due to variation in the index of refraction of the air due to height.
The Elite Human Nature System
 October 2001.
9
www.alisondemarco.com
alison-demarco1@virginmedia.com
The Elite Human Nature System
 October 2001.
+44 7716669566
10
www.alisondemarco.com
alison-demarco1@virginmedia.com
+44 7716669566
The green flash that occurs sometimes as the sun sinks over the horizon is because of
dispersion in the atmosphere.
TWINKLING
Twinkling is due to the light (usually in relation to stars, and therefore starlight)
encountering different variations in air density as it passes through the atmosphere.
Twinkling is usually more apparent on cold, clear windy nights because of the turbulence (=
air flow with random density and velocity changes) caused by the winds.
MIRAGE
The Elite Human Nature System
 October 2001.
11
www.alisondemarco.com
alison-demarco1@virginmedia.com
+44 7716669566
A mirage is defined as a refracted image of something that is normally not there. They are
caused by unusual index of refraction profiles.
Inferior mirages
Inferior mirages are those that one has to look below the horizon to see. This is typified
by the water-in-road (highway mirage) / water on desert (desert mirage) mirage. Inferior
images occur due to skylight being refracted upwards by a heated layer of air above the road
surface.
Superior mirages
Superior mirages are those that appear above the horizon due to light passing upwards
through a warm layer of air being refracted downwards.
The Elite Human Nature System
 October 2001.
12
www.alisondemarco.com
alison-demarco1@virginmedia.com
+44 7716669566
Lateral mirages are reflections of the landscape reflected beyond a wall due to it being
hotter than the surrounding air. It is a type of inferior mirage.
WATER & LIGHT
Light may be reflected or refracted by water. Light is reflected from the surface of the water.
Light can be refracted either from the bottom of the water or from the surface In shallow
water refracted light is more dominant than reflected light which is why shallow water looks
clear. In deep clear water, reflected light (usually from the sky) is dominant, which is why it
looks blue as it masks the waters own colour. If the reflected light is from the landscape, the
mirror image is reflected on the water.
COLOURED WATER
Water can be coloured from suspended particles in the water e.g. algae (green, red or brown)
silt (turquoise) or sulfur (yellow).
Red tide is the term used to describe the rust-coloured patches found in oceans due to
plankton growth.
The Elite Human Nature System
 October 2001.
13
www.alisondemarco.com
alison-demarco1@virginmedia.com
+44 7716669566
Phosphorescent water is the name given to the sea when it sparkles at night. It occurs there
is bioluminescent plankton in the sea.
Foam is white because foam is made up of spherical bubbles. A single sphere reflects
coloured light, but the light from many spheres results in an achromatic sum - white. This is
the same reason that clouds appear white.
Wet spots on a surface appears darker than when the surface is dry because some of the light
entering the water is reflected downwards off the water-air interface and absorbed by the
surface. Therefore less light is reflected.
SURFACE COLOUR AND PATTERNS
Surface colour is due to reflected light on the waters surface.
Glitter describes the reflection of the sun or moon on water. It appears as an elongated path
of sparkling light. It does not occur when the sun is on the horizon.
Moon circles are a term used to describe moon glitter. It appears as rapidly moving closed
loops and they are more prominent when the moon is high and the water is rippled.
Skypools and landpools are distorted images of the sky and land and appear as small
distorted ellipses that move on the surface of the water.
Caustic networks are the pattern of sunlight that are projected onto nearby surfaces, e.g. on
the bottom of the swimming pools.
The Elite Human Nature System
 October 2001.
14
www.alisondemarco.com
alison-demarco1@virginmedia.com
+44 7716669566
OTHER WATER PHENOMENA
Optical manhole is the term given to the circle of light that appears on the water surface if
one looks up when underwater.
Cat’s Paws are the small patches of darkened, dimpled water. They occur when the wind
blows.
Oil slicks form smooth shiny surfaces on the water. The oil film is only a few molecules
thick, and smoothes the water surface as it takes energy from the waves.
The Elite Human Nature System
 October 2001.
15
www.alisondemarco.com
alison-demarco1@virginmedia.com
+44 7716669566
RAINBOWS
Although we normally associate rainbows being made up of seven colours, they can also
contain infrared and ultra violet. These bows are weaker than those in the visible wavelength.
o
Primary rainbows have an arc of 42 with colours running blue to red outward from the
bows center.
Secondary rainbows are sometimes seen outside the primary rainbows. The colours run in
reverse - red to blue outwards. They are fainter and broader than primary rainbows.
Supernumerary bows sometimes appear under a primary rainbow. They are not often seen,
except with garden hose bows.
Alexander’s dark band is the name given to the dark area between primary and secondary
bows.
Fogbows are the pale white bands sometimes seen in fog and clouds.
The Elite Human Nature System
 October 2001.
16
www.alisondemarco.com
alison-demarco1@virginmedia.com
+44 7716669566
FORWARD AND BACKSCATTER PHENOMENA
Heiligenschein, or holy light is the bright colourless glow that sometimes appears around
shadows on mornings before the dew has evaporated. It occurs due to the dewdrops focusing
the sunlight, acting as a lens.
Concentric rings that appear around the sun or moon when viewed through thin cloud are
called coronae (singular = corona). Colour in clouds from corona fragments at large
distances from the sun is called irisation. If the concentric rings are round a specter of the
broken then the correct term is ‘the glory’.
CLOUDS
Clouds are made up of visible air-borne particles of different sizes, suspended in air. They
usually consist of water droplets or ice crystals. Large particles fall as mist or rain.
Clouds appear white because they are made up of spherical particles of different sizes. The
colours from all the spheres mix together, the result is a sum of all the colours - white. This is
the same reason that foam appears white.
Clouds appear dark for two reasons, the first is shadows. If a shadow from a cloud falls onto
another, this one will appear dark. If a thick cloud is back lit then its own shadow will be cast
over it and so will also appear dark. Secondly, the thickness of the cloud can affect the colour
of it. A thick cloud may not allow any background light to shine through it and so appear
dark.
Coloured clouds can occur due to three main reasons. Firstly, the cloud can be translucent
and allow coloured light to shine through it or illuminated by a coloured light e.g. a setting
sun. Secondly, the air between the cloud and the viewer can be such that it absorbs certain
The Elite Human Nature System
 October 2001.
17
www.alisondemarco.com
alison-demarco1@virginmedia.com
+44 7716669566
wavelengths of colour, especially if the distance is great. Thirdly, clouds can reflect the
colour of the ground beneath and beyond it and so take on the colour e.g. a cloud can appear
blue if it is over water. These reflections are called blinks. If the clouds cover a variety of
surface conditions the clouds take on a coloured pattern, called a sky map.
Silver linings of clouds appear when a thick cumulus cloud is back lit, and so the main body
appears dark but the thinner edge lets the light shine through.
Distrails (= Dissipation Trails) is the section of cloud that disappears when a jet flies through
thin clouds. It is the opposite of contrails.
When small scattered clouds seem to congregate near the horizon and thus block it from view
it is known as cloud blocking.
Noctilucent clouds (night-shining clouds) and Nacreous clouds are clouds that can seen
against the night sky after twilight, although it is sometimes possible to see Nacreous clouds
during the day. They are blue, white or even iridescent in colour. Noctilucent clouds are
formed higher than Nacreous clouds.
FOG, HAZE, AND SMOG
Fog is usually water drops, but in cold areas it is possible to get ice fog.
Haze, is made up of cooking smoke, water vapor and dust. It is common in the orient and can
be so thick that it blocks the sun.
Smog is common in the west. It composes of car exhaust and other pollutants.
A blue moon occurs if it is seen through fog, haze smog or smoke.
The Elite Human Nature System
 October 2001.
18
www.alisondemarco.com
alison-demarco1@virginmedia.com
+44 7716669566
LIGHTNING
Lightning is a giant electrical spark. Usually, flashes last for only a fraction of a second, and
usually consists of several shorter strokes, as can be inferred by the flicker. It is possible to
tell how far away the lightning is by counting the delay between the thunder and lightning.
Every second of delay means 0.34 kilometers. However, it is often impossible to hear thunder
that is over 25 km (1 minute delay) away.
Ribbon lightning is formed due to wind.
Ground flashes are lightning discharged between cloud and earth.
Intracloud lightning is lightning within or between clouds.
St Elmo’s Fire is continuous brush discharge from elevated pointed objects.
Ball lightning can be between 2 - 100 centimeters in diameter and appears for a few seconds,
generated from a lightning flash. It usually moves slowly, and it is able to move against the
air currents. It can go through windows without breaking them. Scientists are in disagreement
as to what causes them.
The Elite Human Nature System
 October 2001.
19
www.alisondemarco.com
alison-demarco1@virginmedia.com
+44 7716669566
ICE AND HALOS
Colour and Shape in Ice and Snow
Although snow and ice are thought of as white, they can become brighter than usual and take
on colour in sunlight. If they are white it is called glints, if coloured, sparkles. If a deep hole
is dug in snow it can look blue, due to the absorption of red light. The reason that glaciers can
look green could be due to the presence of algae and air bubbles trapped in it.
Although ice is an octagonal crystal, like a snowflake it is not always angular. Some ice in
clouds, due to temperature changes can become rounded nodules.
HALOS
Halos are bright, colourful arcs, spots or rings seen in cirrus clouds and ice fogs. They are not
always circular and are usually red, orange and/or yellow. They are formed because of
reflection and refraction of light through ice crystals. They are classified according to the
o
particular prisms or crystal faces that produce them, the most common is the 22 halo. When
more than one halo is seen it is called a halo display.
Parhelia (sundogs) are the colourful spots in cirrus clouds.
The Elite Human Nature System
 October 2001.
20
www.alisondemarco.com
alison-demarco1@virginmedia.com
+44 7716669566
Pillars are vertical shafts of light extending from the sun.
Subsuns can only be seen from a plane. They are vertically elongated ellipses below the sun,
seen above the clouds. They are sometimes surrounded by an elliptical ring, a Bottlinger
Ring.
o
Parry arcs are two short arcs found directly above and below the 22 halo.
The Elite Human Nature System
 October 2001.
21
www.alisondemarco.com
alison-demarco1@virginmedia.com
+44 7716669566
ASTRONOMY
THE SUN
The sun is a star which gives out heat and light. It is a ball of gas and has a diameter of over a
100 times greater than the earth. Due to the earth traveling on an elliptical path round the sun,
the distance between them varies. The earth is closest to the sun on January 4th and furthest,
6 months later.
Sunspots are the small dark areas seen sometimes on the solar disk.
A total solar eclipse is very rare. It occurs when the moon completely blocks out the sun
from earth. More common are annular (= ring of photosphere remains visible) and partial
eclipses (-= only part of the sun is hidden).
THE MOON
The Elite Human Nature System
 October 2001.
22
www.alisondemarco.com
alison-demarco1@virginmedia.com
+44 7716669566
The earth has one natural satellite - the moon. It has the colour of brown soil, although some
parts look darker, the maria or ‘seas’. The moon always keeps the same face turned towards
earth.
Earthshine is the faint crescent of light seen on the dark side of the moon. It is reflected
sunlight from the earth.
A lunar eclipse occurs if the moon orbits into the earth’s shadow.
THE PLANETS
There are only five planets that are bright enough to be seen with the naked eye, They are:
Mercury, Venus, Mars, Jupiter and Saturn. Planets do not twinkle as much as the stars.
THE STARS
There are about 6000 stars visible to the naked eye. The brightest is Sirius, which is 300
times brighter than the weakest. Occasionally Sirius can be seen before sunset, otherwise
stars cannot be seen during the day. Most stars appear in pairs although it is hard to
distinguish them. The sky is divided into 88 constellations.
Novae are stars that increase in brightness and then fade, usually only once.
The Milky Way is a band of stars
The Elite Human Nature System
 October 2001.
23
www.alisondemarco.com
alison-demarco1@virginmedia.com
+44 7716669566
A nebula is a glowing cloud of dust and gas.
METEORS AND COMETS
Meteors are lumps of rock or iron that strike the earth’s atmosphere. When it still in space, it
is a meteoroid and when it reaches the ground: meteorite. A fireball is a meteor that it
bright enough to light up the sky, or is visible during the day. If it explodes it is a bolide.
A comet is a lump of ice and dust. The tail is formed when the comet is close to the son and
so evaporates the ice flinging off the dust. The dust is swept back by the solar wind, forming
the tail. The tail always points away from the sun. Halley’s comet appears every 76.9 years, it
has been recorded since 240 BC.
AURORA BOREALIS (NORTHERN LIGHTS) AND AURORA ASTRALIS
Aurorae are multi-coloured flickering, pulsating lights seen in the night sky. They are often a
greenish yellow colour, although can be violet or red. They often form folded arcs or bands
and move slowly across the sky. They are more common towards the poles.
The Elite Human Nature System
 October 2001.
24