The document discusses several optical phenomena that can be seen in the sky including halos, auroras, zodiacal light, rainbows, sundogs, anthelia, light pillars, Alexander's band, afterglows, and the Earth's shadow. These phenomena are caused by the reflection, refraction, and scattering of light through ice crystals, water droplets, and particles in the atmosphere and near space. They include colored or white arcs and spots near the sun, multicolored arcs caused by sunlight through raindrops, bright spots on luminous rings to the side of the sun, and diffuse glows along the ecliptic plane or high in the atmosphere at dusk.

2. A halo is an optical
phenomenon produced by ice
crystals creating coloured or white
arcs and spots in the sky. Many
are near the sun or moon but
others are elsewhere and even in
the opposite part of the sky.

3. An aurora is a natural light display in the
sky, especially in the high latitude regions ,
caused by the collision of solar wind and
magnetospheric charged particles with the
high altitude atmosphere . Most Auroras
occur in a band known as the auroral zone,
which is typically 3 degree to 6 degree wide
in latitude and observed at 0 degree to 20
degree from the geomagnetic poles at all
local times , but often most vividly around
the spring and autumn equinoxes . The
charged particles and solar wind are
directed into the atmosphere by the Earth’s
magnetosphere .A geomagnetic storm
expands the auroral zone to lower latitudes.

4. Zodiacal light is a faint ,roughly
triangular ,diffuse white glow seen in the
night sky that appears to extend up from
the vicinity of the sun along the elliptic or
zodiac .Caused by sunlight scattered by
space dust In the zodiacal cloud ,it is so
faint that either moonlight or light pollution
renders it invisible .The dust forms a thick
pancake –shaped cloud in the solar
system collectively known as the zodiacal
cloud ,which occupies the same plane as
the ecliptic. In fact the zodiacal light
covers the entire sky being responsible in
large part for the total skylight on a
moonless night

5. A rainbow is an optical and meteorological
phenomenon that is caused by reflection and
refraction of light in water droplets in Earth’s
atmosphere resulting in a spectrum of light
appearing in the sky . It takes the form of a
multicolored arc .Rainbows caused by sunlight
always appear in the section of sky directly
opposite to the Sun. All rainbows are full circles ,
however the average observer sees only
approximately the upper half of the arc , the
illuminated droplets above the horizon from the
observer’s line of sight.
In a “primary rainbow” ,the arc shows red on the
outer part and violet in the inner side . This
rainbow is caused by light refracted when
entering a droplet of water ,then reflected inside
on the back of the droplet tend refracted again
when leaving it.

6. A sun dog , is an atmospheric
phenomenon that creates bright spots
of light in the sky, often on a luminous
ring or halo on either side of the sun.
Sundogs may appear as a coloured
patch of light to the left or right of the
sun, 22° distant and at the same
distance above the horizon as the sun,
and in ice halos. They can be seen
anywhere in the world during any
season, but they are not always
obvious or bright. Sundogs are best
seen and are most conspicuous when
the sun is low.

7. An anthelion is a rare optical
phenomenon appearing on the
parhelic circle opposite to the sun as
a faint white halo , not unlike a sundog.
How anthelions are formed is disputed.
Walter Tape, among others, has
argued they are not separate haloes,
but simply where various haloes
caused by horizontally oriented
column-shaped ice crystals coincide
on the parhelic circle to create a bright
spot. If this theory is correct, anthelia
should only appear together with these
other haloes.

8. A light pillar is a visual
phenomenon created by
the reflection of light from ice crys
tals with near
horizontal parallel planar
surfaces. The light can come from
the Sun (usually at or low to the
horizon) in which case the
phenomenon is called a sun
pillar or solar pillar. It can also
come from the Moon or from
terrestrial sources such as
streetlights.

9. 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.

10. An afterglow is a broad high
arch of whitish or rosy light
appearing in the sky due to
very fine particles
of dust suspended in the high
regions of the atmosphere. An
afterglow may appear above
the highest clouds in the hour
of deepening twilight,
or reflected from the
high snowfields in mountain
regions long after sunset. The
particles produce
a scattering effect upon the
component parts of white light.

11. The Earth's shadow or Earth
shadow (also sometimes known
as the dark segment) are names
for the shadow that the Earth itself
casts on its atmosphere. This
shadow is often visible from the
surface of the Earth, as a dark
band in the sky near the horizon.
This atmospheric phenomenon
can sometimes be seen twice a
day, around the times
of sunset and sunrise.