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by: Erin Bleck

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# Astronomy Week 9 Notes EESC1150

Erin Bleck
Harvard University
GPA 3.91

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These notes cover the material during Week 9 of Astronomy at Boston College taught by Professor Kuchar.
COURSE
Astronomy
PROF.
Dr. Thomas Kuchar
TYPE
Class Notes
PAGES
2
WORDS
CONCEPTS
BlackbodySpectrum, DopplerEffect, Kuchar, BC, BostonCollege, astronomy, EESC
KARMA
Free

## Popular in Earth and Environmental Sciences

This 2 page Class Notes was uploaded by Erin Bleck on Friday July 22, 2016. The Class Notes belongs to EESC1150 at Boston College taught by Dr. Thomas Kuchar in Summer 2016. Since its upload, it has received 40 views. For similar materials see Astronomy in Earth and Environmental Sciences at Boston College.

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Date Created: 07/22/16
Notes March 22, 2016 - The hottest stars are the blue stars, and we know because of Wien’s Law - Blackbody Spectrum – How it works o As temperature increases  The peak wavelength (dominant color) becomes bluer (higher energy)  The spectrum becomes brighter at all wavelengths o Temperature is measured by where the peak of the wavelength is on ROYGBIV on the x- axis (does not matter how high it is) o The y-axis measures energy output or luminosity - You observe sunlight as a dark line absorption spectrum - The type of spectrum given off depends on the objects involved (Kirchoff’s laws) o The sun is an absorption line spectrum because of Kirchoff’s third law  A hot dense core (Sun’s surface) surrounded by a cooler, low density outer atmosphere (gas) - All stars have cooler atmospheres surrounding a hotter surface and therefore all produce dark line absorption spectra according to Kirchoff’s third law - The solar spectrum observed changes from where you observe it o Sunlight at top of the atmosphere is at 500nm o 5800K blackbody spectrum is at about 800nm o Spectrum seen through Earth’s atmosphere is at about 1600nm - What can we learn by analyzing starlight? o A star’s temperature  Peak wavelength of the spectral curve o A star’s chemical composition  Dips in the spectral curve or the lines in the absorption spectrum o A star’s motion  Doppler Effect - The Doppler Effect o Definition: “the change in wavelength (of either light or sound) due to the relative motion between the source and the observer along the line of sight” o Astronomers use the Doppler Effect to learn about the motions along the line of sight (radial velocity) of stars and other astronomical objects o Either compresses or stretches the wavelength depending on where you hear that sound or see that light coming and going  Going away = stretching  Coming toward = compressing o Real life examples (anything with “radar”)  Doppler Radar (for weather)  Airplane radar system  Submarine radar system  Radar guns used by law enforcement o When something which is giving off light moves towards (blue) or away (red) from you, the wavelength of the emitted light is changed or shifted o When the source of light is moving away from the observer, the wavelength of the emitted light will appear to increase. We call this a “redshift”  The light won’t look any different to us (will have the same color), but the light will shift a little bit towards the red side of the spectrum o When the source of light is moving towards the observer, the wavelength of the emitted light will appear to decrease. We call this a “blueshift”  The light won’t look any different, but the light will shift a little big towards the blue side of the spectrum o “Along the line of sight” means the Doppler Effect happens only if the object which is emitting light is moving towards or away from you  An object moving “side to side” or perpendicular relative to your line of sight will not experience the Doppler Effect  Could be stationary, but may not be o Astronomy Application (look on PP slide)  Absorption lines will shift towards the red or blue side of the spectrum o Shifts  Redshift (to longer wavelengths): the source is moving away from the observer  Blueshift (to shorter wavelengths): the source is moving towards the observer o The size of the shift tells us the speed  The bigger the shift, the higher the speed  The smaller the shift, the slower the speed o The direction of the shift tells us whether it’s moving towards or away from the observer (red and blue)

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