Analyzing Starlight & HR Diagram

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.

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

Composition of Stars

• Most common element is Hydrogen (H)• Second most common is Helium (He)• Other elements:– Carbon (C)– Oxygen (O)– Nitrogen (N)

Temperature of Stars

Temp & Color

• The hottest starts are BLUE• The coolest stars are RED• Average temperature starts are YELLOW, like

the sun.

Stars Motion: Doppler Effect

• Star moving away, spectra shifted RED• Star moving toward, spectra shifted BLUE

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

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

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.

Questions

• Answer the question on the note guide!