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.