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Human perception of color, fluorescence, applications of fluorescence in biology, why the sky is blue
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Today: Perception of color, Fluorescence, Why sky is blue
Transgenic mouse glowing because of green fluorescent protein from jellyfish (U. Penn)
Homework Question
Thank you Michelle for the pictures with MS Paint!
JohnB. At the time the earth experiences a solar eclipse, the moon observers would see a “lunar eclipse” in where the earth will be almost all light up by the sun, except for the shadow the moon would be casting in the earth. The observers would see the umbra and the penumbra created by the moon on the earth.
MelodyB. If we were standing on the moon during a solar eclipse we would see a small dark shadow on the Earth. This is because the moon in directly between the sun and Earth, is blocking some of the suns rays to the Earth, and is creating a small umbra with a penumbra around the umbra on the Earth.
AnalisaA. During a lunar eclipse the Moon people would see the Earth and that is the side of the Earth that is sleeping- the night side. There would also probably be a ring of sunlight around the Earth- like there is around the moon during a solar eclipse (as viewed on Earth).
Melody A…during a lunar eclipse, when the sun fell directly behind the Earth, the Earth would look darker and there would be a thin red circle outlining the Earth, where the sunlight would be refractring through the thin atmosphere.
I’ll post some photos later on WebCT.
From Veronica http://apod.nasa.gov/apod/ap070302.html
Thank you Michelle Cronoble for the pictures with MS Paint!
Our eye has color receptors and B/W receptors(these are sensitive photon detectors)
Wikipedia
Most people have trichromatic visioncolor blind = dicrhomatic (still have color perception)some reports of tetrachromatic!
Key concept: the “physics of color” is really due to the anatomy and physiology of our eyes and brains
Photon detector
Let’s settle the ROYGBIV issue!
Spectral colors are colors that you see from a single frequency of light (monochromatic)…or colors that make up the spectrum
e.g., magenta is NOT a spectral color
Newton was a little biased in his description of ROYGBIV
It actually should be ROYGCBV…cyan IS a spectral color
Demonstrations of perception of light and color
Perception of white light
Additive primary colors (trichromatic vision)(This is biology!)
Subtractive primary colorsCyan, Yellow, Magenta
Demos – Can you believe your eyes?
Bidwell’s disc (this is a tricky one)
Color wheel and optical discs
Clicker Question—Spectral colors
Which of the following is NOT a spectral color? Reminder: a spectral color is a “pure” color that can be created by a single frequency of light.
A) MagentaB) CyanC) YellowD) BlueE) Green
Clicker Question—Spectral colors
Which of the following is NOT a spectral color? Reminder: a spectral color is a “pure” color that can be created by a single frequency of light.
A) Magenta is a mixture of blue and redB) CyanC) YellowD) BlueE) Green
These CAN be created by mixtures, but also are spectral colors
Fluorescence(1) Molecule absorbs a photon of a certain energy(2) Molecule emits a photon of lower energy (nanoseconds delay)
Fluorescence(1) Molecule absorbs a photon of a certain energy(2) Molecule emits a photon of lower energy (nanoseconds delay)
UV Light
Phosphorescence is similar to Fluorescence, but slower
UV Light demo…if available
Clicker Question—Fluorescence
Which of the following is a possible kind of fluorescence?
A. One red photon absorbed, one green emittedB. One red photon absorbed, one blue emittedC. One infrared photon absorbed, one blue
emittedD. One ultraviolet photon absorbed, one blue
emittedE. One blue photon absorbed, one ultraviolet
emitted
Clicker Question—Fluorescence
Which of the following is a possible kind of fluorescence?
A. One red photon absorbed, one green emittedB. One red photon absorbed, one blue emittedC. One infrared photon absorbed, one blue
emittedD. One ultraviolet photon absorbed, one blue
emittedE. One blue photon absorbed, one ultraviolet
emitted
Conservation of energy! High energy photon absorbed, lower energy emitted.
Fluorescence is a very powerful tool in biology
A single protein can be “labeled” fluorescently
Different colors can label different proteins
“Quantum dots” of various colors
Lung epithelial cells (DNA blue, cilia red)
Fluorescence Microscopy
Filters allow blocking the excitation light (so only light comes from fluorescence)
For example, we can see proteins “absorbed” by cells
“Chinese Hamster Ovary” cells, up-taking quantum dots coated with protein
Diane Lidke, UNM HSC
There are naturally fluorescent proteins
GFP (“Green Fluorescent Protein”) from the jelly fishOsamu Shimomura and Roger Y. Tsien—2008 Nobel Prize, Chemistry
Scientists know how to add GFP to the genome of a cell-> ANY protein can be made to glow green!
GFP Mouse!
In addition to being absorbed, light can also be scattered
The atmosphere scatters some sunlight
Light (an oscillation) can cause molecules to resonate
The closer to the resonant frequency, the more scattering(Imagine the “resonant square” demo…or acoustic resonance)
Visible light is below the “resonant” frequncey of Nitrogen
Clicker Question—Scattering
Which of the following is closest to the resonant frequency of a nitrogen molecule?
A. Red lightB. Blue lightC. Green light
Clicker Question—Scattering
Which of the following is closest to the resonant frequency of a nitrogen molecule?
A. Red lightB. Blue lightC. Green light
The intensity of light waves scattered by the atmosphereis higher at higher frequencies
Intensity (frequency)4
So why is the sky blue? Why are sunsets red?
Lunar eclipse
NASA
The blue sky and red sunsets are the same effect!
Sunset demo
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