ASTR 1120 Light: The Cosmic Messenger General Astronomy: Stars & Galaxies � NNOUNCEMENTS: NNOUNCEMENTS: - First homework on Mastering Astronomy: due Thursday, 09/10, by 5pm (late penalty) - Math review session Thursday 09/03: 5-7pm in Ramaley Biology, RAMY N1B23 - First observing session at Fiske TOMORROW Light is a form of � NERG � L I G H T • For nearly all astronomical objects, light brings us our only information • Need to understand what light is and how it can be interpreted • White light is made up of many different colors
Four Ways in Which Light can Four Ways in Which Light can Interact with Matter Interact with Matter 1. Emission – matter releases 1. Emission – matter energy as light releases energy as light 2. Absorption – matter takes 2. Absorption – matter energy from light takes energy from light 3. Transmission – matter 3. Transmission – matter allows light to pass through it allows light to pass 4. Reflection – matter repels through it light in another direction 4. Reflection – matter repels light in another direction Four Ways in Which Light can Four Ways in Which Light can Interact with Matter Interact with Matter 1. Emission – matter 1. Emission – matter releases energy as light releases energy as light 2. Absorption – matter 2. Absorption – matter takes energy from light takes energy from light 3. Transmission – matter 3. Transmission – matter allows light to pass allows light to pass through it through it 4. Reflection – matter 4. Reflection – matter repels light in another repels light in another direction direction
Clicker Question Clicker Question Why is a rose red? Why is a rose red? A. The rose emits red light. A. The rose emits red light. B. The rose absorbs red light. B. The rose absorbs red light. C. The rose transmits red light. C. The rose transmits red light. D. The rose reflects red light. D. The rose reflects red light. Light as a WAVE Wave-Particle Duality of Light = AMPLITUDE Anatomy of a Wave • Speed of light is • Light can behave like a wave the SAME for all wavelengths – Frequency, wavelength, amplitude • The shorter the • Light can also behave like a particle wavelength, the – Photons, discrete amounts of energy = more cycles pass per second “quanta” – Train analogy… • How to remember equation? – Unit Analysis!
Photon Energy Depends on Light as a PARTICLE Frequency/and ? • Light can also be thought of as a particle � “photon” NOT proton! A photon is a mass-less particle of electromagnetic radiation energy Wave-particle duality seen in other E � f particles (e.g., electrons) as well E � 1 / � Clicker Question Photon Energy Depends on Frequency/Wavelength What is LIGHT? A. Light is a wave, like sound only much faster. B. Light is like little particles. Each one is a photon. C. Light is the absence of dark. D. A kind of energy we model with some of the properties of waves and some properties of particles. E � f E. Light is the sensation you feel when hit by E � 1 / energy, visible or invisible.
Clicker Question Clicker Question When compared to RED light ( � = 700 nm), Blue light ( � = 400 nm) is: What is LIGHT? A. Light is a wave, like sound only much faster. B. Light is like little particles. Each one is a A. Longer wavelength photon. B. Lower Frequency C. Light is the absence of dark. C. Higher energy photons D. A kind of energy we model with some of the properties of waves and some properties of D. Faster photons particles. E. None of the above E. Light is the sensation you feel when hit by energy, visible or invisible. The Electromagnetic Spectrum Clicker Question When compared to RED light ( � = 700 nm), Blue light ( � = 400 nm) is: A. Longer wavelength B. Lower Frequency C. Higher energy photons D. Faster photons E. None of the above
Light as Information Bearer But first we need a review of… Matter: a Material World We can separate light into its different wavelengths (spectrum). • ATOM : nucleus made of protons and neutrons A cloud made of electrons surrounds the nucleus Electrons are held onto the atom by electric force. Electrons have negative electric charge, protons are positive. Neutrons are neutral. By studying the spectrum of an object, we can learn its: Composition • Electrically neutral atoms have the same number of protons and Temperature • electrons Velocity • Periodic Table of the Elements Atoms Involve Big Empty Spaces Atomic Number = # of protons in nucleus Atomic Mass Number = # of protons + neutrons
Hydrogen: simplest and Helium most common Carbon Isotopes The number of protons ( !"#$%& %&'()$ ()$*+, +, !" "#$%&%#'(&)*(+"%"#(&'%),"#$(-)#%."(.(-(,'/ • Mostly an atom will have a certain “normal” number of neutrons along with the protons. • But occasionally, an atom will have a few more or less neutrons than normal. This is called an isotope of that element.
Clicker Question Clicker Question Deuterium is an isotope of Hydrogen. Deuterium is an isotope of Hydrogen. Which of the following makes sense Which of the following makes sense for the composition of Deuterium? for the composition of Deuterium? A. 1 proton, 0 neutrons, 1 electron A. 1 proton, 0 neutrons, 1 electron B. 2 protons, 0 neutrons, 2 electrons B. 2 protons, 0 neutrons, 2 electrons C. 2 protons, 2 neutrons, 2 electrons C. 2 protons, 2 neutrons, 2 electrons D. 1 proton, 1 neutron, 1 electron D. 1 proton, 1 neutron, 1 electron E. 1 proton, 0 neutrons, 0 electrons E. 1 proton, 0 neutrons, 0 electrons What if two or more atoms combine to What if an electron is missing? form a particle? ion molecule p + p + p + 8p + 8n atomic number = 1 H +1 H 2 O (water) atomic mass number = 1
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