Analyzing Starlight & HR Diagram

1. Analyzing Starlight & HR Diagram

2. Stars • Star: a ball of gases that gives off electromagnetic radiation in the form of heat and light • Stars look white from Earth but can be red, blue, white, orange, or yellow. • The Sun is a yellow star.

3. Analyzing Starlight • Astronomers use an instrument called at spectrograph/spectroscope • Device separates light in to different wavelengths and colors = Spectrum • All stars have dark-line spectra • Spectrum reveals a stars composition and temperature

4. Composition of Stars • Most common element is Hydrogen (H) • Second most common is Helium (He) • Other elements: • Carbon (C) • Oxygen (O) • Nitrogen (N)

5. Temperature of Stars

6. Temp & Color • The hottest starts are BLUE • The coolest stars are RED • Average temperature starts are YELLOW, like the sun.

7. Stars Motion: Doppler Effect • Star moving away, spectra shifted RED • Star moving toward, spectra shifted BLUE

9. H-R Diagrams An H-R Diagram is… • A graph of star’s TEMPERATURE and BRIGHTNESS. • It also shows STAR’s COLOR, since color is related to temperature • Stands for Hertzsprung-Russell

12. Notice… • Temperature DECREASES as you move to the right () on the X-axis • Absolute Magnitude INCREASES as you move up on the Y-axis • Negative absolute magnitude values are BRIGHTER than positive absolute magnitude values

13. A Star… • Starts off in the lower right hand corner in THE MAIN SEQUENCE when it first becomes a star. • As it gets HOTTER and BRIGHTER, it moves up the main sequence. • Then it moves to the upper right section when it changes to GIANTS. • It ends in the lower left section when it changes to a WHITE DWARF.

14. Questions • Answer the question on the note guide!