astronomy2 - I Light – What is it and how does it work a...

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I. Light – What is it and how does it work? a. Astronomy is an observational science, so we see light to make these observations b. Light carries far more than just positional information c. What is light? i. Is light a wave or a bullet of particles? ii. Slit experiment 1. Send light though a narrow slit 2. If light were bullets, it would go straight through and illuminate a horizontal slit where it hits the wall 3. If light were waves, then you would see it shoot through the opening and spread out spherically beyond slit a. CALLED DEFRACTION 4. Even if slit was horizontal, we did not see a horizontal slit, so we should think of light as waves (at least if we’re discussing light at a macroscopic level with human sized distances) d. Properties and behavior of Generic Waves i. The wave/energy it carries travels left to right ii. Imagine a sin wave iii. In a wave there are individual oscillators or pieces of materials that only goes up or down and make no overall progress iv. Electric and magnetic fields are what “waves” light 1. This is what you create when you shake an electric charge which creates a wiggle v. There’s no matter wiggling in a light wave, its just these fields 1. Communications of electric charges 2. Light waves can travel through totally empty space unlike sound waves which need air to travel in space e. Wave Terminology i. Amplitude is the strength of an electro magnetic fields or the brightness of light ii. Lambda is crest to crest distance (wavelength) 1. Corresponds to color of the light 2. Wavelength for violet light is 400 nanometers and red light is 700 nanometers a. Red light has longer wavelength b. Violet light has shorter wavelength c. Red -> Orange -> Yellow -> Green -> Blue -> Violet is visible light iii. Frequency is how many waves pass per second (crests per second) 1. Measured crest by crest f. Travel Velocity of light i. (Lambda)(Frequency) = C 1. L = Wavelength
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2. F = waves per second 3. C = speed of light (3.00 * 10^8 m/s) ii. Lambda is measured in meters and frequency is measured in (1/second) 1. Unit is Meters/Second iii. If one part of this formula changes, then the others must change as well to keep the speed of light constant 1. If Lambda goes down, there will be more waves per second (higher frequency) 2. If Lambda goes up, there will be less waves per second (lower frequency) II. Light Waves + Information a. A lot of important information is encoded by light waves rather than just simple positioning information i. Jumping electrons in star’s atoms certainly count as wiggling electric charges that create a wiggling electric field ii. Starlight can encode information about the stars makeup 1. Two Main encoding or information schemes of today: Defuse Gas emission or Absorption Spectrum 2. Thermal radiation spectrum b. Defuse gas emission or absorption i. Atoms have positive charge at nucleus w/ negatively charged electrons around nucleus 1. Key Point: in any given atom, the electrons cant exist anywhere around the nucleus, they can only live in discrete states, or steps (energy levels) ii.
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