Transcript Naturally Occuring Optical Phenomena

Naturally Occurring Optical
Phenomena
Apparent Depth
Dispersion
• Dispersion is the refraction of white light into
separate wavelengths or colours.
Primary and Secondary Rainbows
Three things must happen for you to see a rainbow’s colors:
1) The sun must be shining
2) The sun must be behind you
3) There must be water drops in the air in front of you
When sunlight shines into a water drop, it refracts the light and
separates it into colors (like a prism).
Light is refracted, reflected, and refracted again for primary
rainbows.
Light is refracted, reflected, reflected again, and refracted for
secondary rainbows. (See the following diagram)
• The smaller the wavelength of the light, the greater the
angle of refraction as it exits (Violet light is refracted the
most)
• The colors of the rainbow are divided as they are because
the drops at the top are reflecting red light in the direction
of our eyes and the drops at the bottom are reflecting violet
light in the direction of our eyes (primary).
• Only the color that we see in each band is being reflected
directly to our eyes.
• The other colors reflected by each drop are traveling at
angles that are not incident with our eyes.
Mirages
• Both refraction and TIR
play a role in forming a
mirage.
• What different
mediums are involved?
• A mirage is a distant object produced as light refracts through
air of different densities.
• The air closer to the ground is warmer (less dense)
• Since the light rays pass through layers of air with
progressively lower indices of refraction, eventually the light is
totally internally reflected.
Halos and Sun dogs
• A halo is produced by the
ice crystals in cirrus clouds
in the upper troposphere.
• Six-sided ice crystals that
make up those clouds act
as prisms and mirrors,
refracting and reflecting
sunlight between their
faces.
• A sun dog occurs when
light refracts through flat,
horizontal ice crystals.
Red Suns and Blue Moons
RED SUN
• Near sunrise/sunset, the angle of the sun’s rays strike the
atmosphere at a lower angle than during the day.
• Therefore light enters a deeper layer of the atmosphere and
most of the shorter wavelengths of visible light scatter away.
• The light that reaches our eyes are the longer wavelengths,
orange-yellow (clean atmosphere) and red (polluted
atmosphere).
• Blue moons occur when large particles scatter longer
wavelengths of visible light and shorter wavelengths reach our
eye.