Human perception of color, fluorescence, applications of fluorescence in biology, why the sky is blue

1. Today: Perception of color, Fluorescence, Why sky is blue Transgenic mouse glowing because of green fluorescent protein from jellyfish (U. Penn)

2. Homework Question Thank you Michelle for the pictures with MS Paint! John B. 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. Melody B. 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. Analisa A. 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.

3. 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!

4. Our eye has color receptors and B/W receptors (these are sensitive photon detectors) Wikipedia Most people have trichromatic vision color 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

5. 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

10. Fluorescence (1) Molecule absorbs a photon of a certain energy (2) Molecule emits a photon of lower energy (nanoseconds delay)

11. Fluorescence (1) Molecule absorbs a photon of a certain energy (2) Molecule emits a photon of lower energy (nanoseconds delay) UV Light

19. In addition to being absorbed, light can also be scattered

23. So why is the sky blue? Why are sunsets red? Lunar eclipse NASA

24. The blue sky and red sunsets are the same effect!

25. Sunset demo