29:50 Modern Astronomy
Fall 1999
Lecture 3 ...August 27, 1999
The Sun : Part 3

Watch the skies! Watch the skies! Go out at about 9PM and look straight overhead. You will see the star Vega (routing point for Jodie Foster in Contact), the second brightest star visible from the part of the planet. A star like the Sun in some ways, different in others.
In last week's thrilling episode... Big Questions about the Sun

1. Why does it shine?
2. What is it made of?
3. Where does it get its energy?
4. How old is it?

Last time started talking about electromagnetic radiation and its properties.
The electromagnetic spectrum What is the wavelength of light to which the human eye is sensitive? Answer: 0.00000040 - 0.00000070 meters. Bah! Use scientific notation: meters.
A lot of other phenomena are identical to light except the wavelength is different.
Transparency, Figure 6-5.
Longer wavelength: infrared (IR), microwave, radio waves.
shorter wavelength: ultraviolet (UV), X-rays, Gamma rays.

How is electromagnetic radiation produced? A; lots of ways. One important way is blackbody radiation. Hot objects emit light. Hotter objects emit more light.
illustration/demonstration with light bulb.

To talk about production and characteristics of light, we need to introduce a definition: a spectrum. Spectrum is intensity of light versus (``is a function of'', in fancy mathematical language) wavelength.
Graph of intensity of light versus wavelength.

• Experiments in the golden days of yesteryear
• Systems of Temperature
• The relation between color and temperature: Wien's Law
• About this document ...