Stars and Galaxies

28.1 A Closer Look at Light

Chapter 28

What is Light?• Light is a form of Electro Magnetic Radiation that travels in

waves• All EMR’s travel at 300,000 Km/sec (186,000 mi/sec) - The

Speed of Light!

• EMR’s are measured in wavelengths– Which is the distance from one

crest to the next• EMR’s are arranged into the electromagnetic spectrum

• Electromagnetic Spectrum is arranged from short wavelength’s to long wavelength’s

• High frequency = short wavelength’s

• Stars emit a wide range of energies

• White light is actually color of rainbow

• Light passes through a prism and is refracted (bent) into visible spectrum

• Astronomers use spectra to learn about distant stars

• Spectral Types (Kirchhoff’s spectral laws)– Use pg 614 in book and write in information for Homework!

1. Continuous spectrum – unbroken color band created by a luminous solid or liquid, and hot compressed gases

2. Bright line spectrum (Emission Spectra)– form chemical elements in the gaseous state that are luminous. Each element has a unique bright line spectra.

3. Dark line spectrum (Absorption Spectra)– form when light of a continuous spectrum passes through a cooler gas. Gas absorbs same wavelengths it would emit if it were hotter.

Spectroscopy• Science dealing with the analysis of the spectrum of

light.

• Astronomical applications:

– 1. Element composition of stars

– 2. Temperatures of stars

– 3. Relative motion of stars

Spectra Analysis Video

• Emission Spectrum of Hydrogen

Absorption Spectrum of Hydrogen

Suns Visible Spectra

Doppler effect • the apparent change in the wavelength of light that

occurs when an object is moving toward or away from the earth.

• Star Movement

– Red Shift – Spectrum of an object that is moving away from the earth.

– Blue shift – spectrum of an object moving toward earth

Doppler Effect

• Emission spectrum of hydrogen

Redshift: This spectrum shows hydrogen shifted to the red end of the spectrum. This star is moving away from Earth.

Blueshift: This spectrum shows hydrogen shifted to the blue end of the spectrum. This star is moving toward Earth.