1. Our Universe

2. Stars

3. Different Types of Stars
Giants D. Supergiants
White Dwarfs E. Sun
Main Sequence

4. Sagittarius Star Cloud, HST
Star Color
Stars have different colors
Some look red (like Betelgeuse), some
look more yellow (like the Sun), and some
look blue or blue-white (like Sirius)
Color is directly related to temperature
Light is not sensitive to the details of
the star's composition but to its
temperature
(according to which law?)
Astronomers can determine:
1. the surface temperature of a star by
measuring its color
2. the composition of its outer layers by
looking at its spectral lines
Wien’s law: T=k/lambda(max)
Sun

5. Star color and brightness
Is a star’s color (temperature) related to its size?
Is the relation the same for all stars?
Are there different kinds of stars?

6. Electromagnetic Radiation
Energy that travels through space in waves
Stars give off electromagnetic radiation in different forms
Each form has its own wavelength
Radio Waves
Infrared Rays
Visible Light
Ultraviolet Light
X-Rays
Gamma Rays

7. Continuous spectrum and Absorption spectrum
A Any visible white light consists of millions of colors, including the seven very obvious colors: red – orange – yellow – green – blue – indigo and violet.
A hot glowing object like a wire inside the bulb gives off a continuous spectrum.
A continuous spectrum is a spectrum that shows all colors.

8. Continuous Spectrum
A rainbow is an example of a continuous spectrum. Most continuous spectra are from hot, dense objects like stars, planets, or moons.. Any solid, liquid and dense (thick) gas at a temperature above absolute zero will produce a thermal spectrum.

9. Absorption Spectrum
Because each element in this world absorbs a color or more of the continuous spectrum, the elements in the atmosphere of a star emits an absorption spectrum rather than a continuous spectrum.
A absorption spectrum is produced when light from a hot solid or dense gas passes through a cooler gas (which is the atmospheric gases of the star in this case)

10. Measuring the chemical composition of a star from its absorption spectrum

11. Identifying the composition of star’s atmosphere using its absorption spectrum

12. Composition of a typical star

13. Here are spectra for some elements common in the atmospheres of stars:
In a star, these elements absorb light at their special frequencies. On the following pages, you will see both the elements for comparison and a star's spectrum. Your job is to identify all the elements you can detect in the star's atmosphere.

14. Here are spectra for some elements common in the atmospheres of stars:
Here is the spectrum of a mystery star:
Which elements are present?

15. Yes, you are correct!
The mystery star:
has the following elements.
Hydrogen
Iron

16. Here is the spectrum of a mystery star:
Here are spectra for some elements common in the atmospheres of stars:
Here is the spectrum of a mystery star:
Which elements are present?

17. Yes, you are correct!
The mystery star:
has the following elements.
Calcium
Hydrogen
Magnesium
You have identified all the elements

18. Assignment 1
What is the supernova and how does it differ from the black hole?