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