CH. 4

 Energy that can travel through space from one point to another without any physical link  We can see stars explode, but why can’t we hear them?

 Model A Light is a wave that is a mix of electric and magnetic energy  Model B Stream of particles called photons  Photons - packets of energy Electrons & protons move in straight line that can act like waves

 Wave – Particle Duality Scientists use which ever model the best fits a particular situation Ex. Light reflecting off mirror (model B - photons) Ex. Light focusing through a lens (model A - waves)

 Brightness Measures the amount of energy carried by the light  Height of wave (wave model)  Number of photons (particle model)  Color Visible portion of the electromagnetic spectrum Determine light’s wavelength ( )  Red = long, Blue = short White light: Mix of all colors discovered by Newton with a prism and lens

 Electromagnetic Spectrum Spectrum of all different types of electromagnetic waves  Use different waves to see what’s going on in space besides just visible light. Radio Waves – longest  Use every day – radio telescopes Infrared – longer than visible light  Can’t see it, but feel as heat UV Light – shorter than visible light

 Infrared light is the Light that we perceive as heat.

 Almost everything Gives off Radio light. Including you. Very low Energy light.

 A slightly higher energy light that can interact with different substances and give them, different visible colors. UV - Rings UV - Saturn Visible Light

 E = hc/ E = energy h = constant c = speed of light (constant) = wavelength  Means: Shorter the wavelength, the higher the energy

 As object’s temp. increases: Radiates light more strongly at shorter Color changes:  Red (long ), Yellow (medium ), Blue (short ) Allows astronomers to predict temp. of stars  Black Bodies Objects that absorb all radiation Reflect no light and looks black when cold

 See colors due to excited electrons Absorption  Atoms gain energy exciting electrons to higher energy levels Emission  Atoms lose that energy and emit a specific color of light

 Astronomers use spectrums to study star composition Absorption Spectrum – shows λ of light absorbed Emission Spectrum – shows λ of light emitted Each λ of light that is absorbed or emitted can be match to a specific element

EMMISION SPECTRUM ABSORPTION SPECTRUM

 Change in caused by motion towards or away from us  Used to find/measure speed and direction of objects Ex. Sirens  Red Shift appears to increase - Object is moving away  Blue Shift appears to shorten - Object is moving closer