Lecture 4

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University of Virginia *

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1210

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Astronomy

Date

Oct 30, 2023

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docx

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Uploaded by ProfessorLightningPuppy25

Announcements ● HW 2 due Wednesday ● Telescope observing @ O’hill lab due late in the semester but open now ○ Do after rush Spectroscopy Basics James Clerk Maxwell (1831 - 1879) ● Scottish mathematician and physicist ● Known for deriving the formulas for the classical theory of “electromagnetism” Maxwell’s revolution ● As charged particles oscillate up and down, a changing electric field is created ● This changing electric field generates a magnetic field ● This pattern of oscillating electric and magnetic field spreads out in a wave pattern ○ The speed of propagation is at the speed of light! Electromagnetic Radiation ● The first intentional radio signals were produced by Hertz using this technique in 1887 ● Hertz was motivated by Maxwell’s new theory ● See: https://phet.colorado.edu/en/simulations/radio-waves Light: Electromagnetic Waves ● A light wave is a vibration of electric and magnetic fields ● Light interacts with charged particles through these electric and magnetic fields Properties of waves ● Wavelength x Frequency = speed ● Or (lambda, wavelength) x (nu, frequency) = speed ? ? Wavelength and Frequency ● Longer wavelength means lower frequency ● Shorter wavelength means higher frequency Wavelength, Frequency, and Energy ● E = h x f (Photon energy) ● The higher the frequency the higher the energy The Electromagnetic Spectrum ● Electromagnetic waves can have almost any wavelength but they all have the same speed (c) ●

Continuous Spectrum ● The spectrum of a common (incandescent) lightbulb spans all visible wavelengths, without interruption Absorption Line Spectrum ● A cloud of gas between us and a lightbulb can absorb light of specific wavelengths, leaving dark absorption lines in the spectrum Emission Line Spectrum ● A thin or low-density cloud of gas emits light only at specific wavelengths that depend on its composition and temperature, producing a spectrum with bright emission lines Chemical FIngerprints ● Because those atoms can absorb photons with those same energies, upward transitions produce a pattern of absorption lines at the same wavelengths What is the Structure of Matter ● Atoms are composed of the fundamental particles: ○ Protons (positive charge) ○ Electrons (negative charge) ○ Neutrons (no charge) ● Protons and neurons (located in the nucleus) are 1836 times more massive than electrons Atomic Terminology ● Atomic number = # of protons in nucleus ● Atomic mass number = # of protons + neutrons ● Molecules: consist of two or more atoms (H20, CO2) ● Isotope: same # of protons but different # of neutrons ( 4 He, 3 He) Periodic table of elements can lick my balls

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