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astronomy

# astronomy - Astronomy 4.x.1 10:49 AM Page 1 ASTRONOMY...

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SPARK CHARTS Astronomy page 1 of 6 This downloadable PDF copyright © 2004 by SparkNotes LLC. SPARK CHARTS TM ASTRONOMY SPARK CHARTS T SPARK CHARTS TM Copyright © 2003 by SparkNotes LLC. All rights reserved. SparkCharts is a registered trademark of SparkNotes LLC. A Barnes & Noble Publication 10 9 8 7 6 5 4 3 2 1 Printed in the USA \$4.95 \$7.95 CAN LIGHT Wave description: The periodic oscillation of electric and magnetic fields in space. Characterized by the following: 1. Frequency of the oscillation, ν , measured in cycles per second (hertz). 2. Wavelength of the oscillation, λ , measured in meters. This is the distance from one peak to the next. Wave equation: All light travels at a finite speed, c = 3 × 10 8 meters per second. This results in an inverse relationship between the frequency and wavelength. Mathematically: c = λ × ν . Thus, light with a high frequency has a short wavelength, and vice versa. Particle description: A stream of photons , individual particles of light that each carry a specific amount of energy, which is directly proportional to the frequency of the light. Mathematically, Planck’s Law: E = E , energy (Joules, J) ν , frequency (Hertz, hz) h = 6 . 63 × 10 34 , Planck’s constant (J × s) Light with a high frequency (short wavelength) is also very energetic. Electromagnetic spectrum : The collection of all frequencies of light. Includes (in order of increasing energy) radio , infrared , visible , ultraviolet , x-ray, and gamma ray frequencies. Different physical processes in the universe emit radiation at different frequencies, so each frequency band probes different phenomena in the universe. Light quantities: Energy: The capacity to cause change (Joules, J) Power: Energy emitted per unit of time (J/s= Watts, W=J s 1 ) Luminosity: Light energy emitted per unit time (power from a star) ( J s 1 =Watts, W) Flux: Energy emitted per unit time per unit area ( J s 1 m 2 = Wm 2 ) Mathematically, F = L 4 πD 2 F , flux from surface of a spherical object (W m 2 ) L , luminosity of object (W) D , distance to object (m) Spectroscopy: The technique astronomers use to separate light into its intensity at different wavelengths or spectrum. Components: 1. Continuum: The smooth part of the spectrum (see Figure 1). Most objects emit light at all frequencies, but the shape of the spectrum depends on the physical process that produces the light. Blackbody: A dense object that reflects no light, and thus emits light only because of the thermal motion of its atoms, measured by its temperature. Most objects produce their own continuum approximately as a blackbody (e.g., the Sun, an incandescent light bulb, and the human body). The shape of the curve depends only on temperature. A hot object emits more light at higher frequencies (higher energies) than a cool object (e.g., hot stars appear blue, cool stars appear red).

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astronomy - Astronomy 4.x.1 10:49 AM Page 1 ASTRONOMY...

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