Sun, Earth, and Sky
Preface

Perceiving invisible worlds Julia Lang - a child's eye


New windows on the universe (and the Sun)


1. Spectral regions - radi, x-ray, UV = ultraviolet
2. Spacecraft - cameras, subatomic particles, magnetic fields


Voyage - center of Sun to our transparent air


For example - see two Sky and Telescope articles August, September 1996
and Scientific America article, March, 1997


Good Day, Sunshine Sun in Religion, Art, Poetry

Egyptians - Luxor, Obelisks, Sun-god Ra
Bible - Genesis - Let There Be Light Also The light shines in the darkness And the darkness has not overcome it. John.Chp.1,verse 5
Aztecs - victims to Sun god
Shintoism - Japanese Sun-worship - Land of the Rising Sun
Chapter Frontispieces - Miro, Monet, Turner, Van Gogh, etc...
Light = truth, beauty, good
Dark = evil, bad
Fire of Life - Light to see, heat to warm, energize, Earth-photosynthesis


Sun as a Star

1. Unique aspects of Sun - nearby, very bright, see (resolve) surface details
2. Sun is a Second Generation Star - Sun contains heavy elements synthesized inside other stars and ejected into interstellar space from which Sun formed. (Also calcium in our teeth, iron in our blood.)
3. Sun is 4.6 billion years old - Universe is about 15 billion years old so the Sun is a lot younger than the Universe.
4. Sun's ingredients - mostly hydrogen. Hydrogen = lightest known element. Also helium - first discovered in Sun is the second - most - abundant element in the Sun and heavier elements - less abundant. In contrast, Earth's atmosphere cannot retain hydrogen.


Atoms and their Spectral Signatures

1. Atoms are mostly empty space.
2. Only certain electron orbits are allowed, and radition occurs only in changing orbits.
3. So raditation is only at certain wavelengths, called spectral lines that fingerprint the atom.


Radiation at Different Wavelengths

1. Wavelength of radiation = distance between wave crests
2. All radiation travels at the velocity of light = c
c = 299793 kilometers per second
3. Wavelength x frequency = c
Short wavelength = high frequency and vica versa
4. Spectrum

x-ray................uv................|invisible|...............infrared...............radio

|.......................|......................|..........................|.......................|

________________________________________________________________

short-----------------------------------wavelength-------------------------------------->long


A hot gas like the Sun emits radiation at all wavelengths, but the intensity of light depends on the wavelength.
We see by visible light.
Rattlesnakes see their prey by infrared light. (for prey heat)
Falcons see by ultraviolet light (for prey urine)


Invisible Cosmic Radiation

1. Our atmosphere totally absorbs x-rays and most ultraviolet = uv, radiation
2. We see this cosmic radiation using space craft
3. From ground see visible and radio waves


Radiation Has Energy

1. Photon energy = constant x frequency
= another constant divided by wavelength

2. Shorter waves have more energy
ENERGY
X-ray High See Bones
ultraviolet Medium Sunburns
visible Low See Skin

3. Hotter gas emits more energy at shorter wavelengths
Temperature Wavelength
Million degrees X-rays
6,000 Visible- Sun surface
100 degrees Radio - space between stars